Using Light (Sunlight, Blue Light & Red Light) to Optimize Health

00:00:00.000 | - Welcome to the Huberman Lab Podcast,

00:00:02.260 | where we discuss science and science-based tools

00:00:04.880 | for everyday life.

00:00:05.900 | I'm Andrew Huberman,

00:00:10.200 | and I'm a professor of neurobiology and ophthalmology

00:00:13.320 | at Stanford School of Medicine.

00:00:15.260 | Today, we are going to discuss light

00:00:17.160 | and the many powerful uses of light to optimize our health.

00:00:20.880 | We're going to discuss the use of light

00:00:22.680 | for optimizing skin health, appearance, and longevity,

00:00:26.280 | for wound healing, for optimizing hormone balance,

00:00:29.640 | and for regulating sleep, alertness, mood,

00:00:32.680 | and even for offsetting dementia.

00:00:35.000 | One of the reasons why light has such powerful effects

00:00:37.540 | on so many different aspects of our biology

00:00:40.240 | is that it can be translated into electrical signals

00:00:43.800 | in our brain and body,

00:00:45.080 | into hormone signals in our brain and body,

00:00:47.600 | and indeed into what we call

00:00:49.400 | cascades of biological pathways,

00:00:51.560 | meaning light can actually change the genes

00:00:54.720 | that the cells of your bodies express,

00:00:56.680 | and that is true throughout the lifespan.

00:00:59.120 | Today, I will discuss the mechanisms

00:01:00.760 | by which all of that occurs.

00:01:02.640 | I promise to make it clear for those of you

00:01:04.480 | that don't have a biology background,

00:01:06.360 | and if you do have a biology background,

00:01:08.320 | I'll try and provide sufficient depth

00:01:10.080 | so that it's still of interest to you,

00:01:12.040 | and I promise to give you tools,

00:01:14.260 | very specific protocols that are extracted

00:01:16.240 | from the peer review literature

00:01:17.640 | that will allow you to use different so-called wavelengths,

00:01:20.660 | which most of us think of as colors of light,

00:01:23.280 | in order to modulate your health

00:01:25.600 | in the ways that are most important to you.

00:01:27.980 | For those of you that are thinking

00:01:28.980 | that the use of light to modulate health

00:01:30.800 | falls under the category of woo science,

00:01:32.680 | pseudoscience, or biohacking,

00:01:35.120 | well, nothing could be further from the truth.

00:01:37.820 | In fact, in 1903, the Nobel Prize was given

00:01:41.140 | to Niels Vinson, he was Icelandic, he lived in Denmark,

00:01:44.700 | for the use of phototherapy for the treatment of lupus.

00:01:48.800 | So there's more than 100 years of quality science

00:01:52.140 | emphasizing the use of light,

00:01:54.680 | and as you'll soon see,

00:01:55.960 | the use of particular wavelengths or colors of light

00:01:59.960 | in order to modulate the activity of cells

00:02:02.360 | in the brain and body.

00:02:04.160 | So while it is the case that many places

00:02:07.380 | and companies are selling therapies and products

00:02:10.360 | related to the use of flashing lights and colored lights,

00:02:14.520 | promising specific outcomes

00:02:16.440 | from everything from stem cell renewal

00:02:18.820 | to improvement of brain function,

00:02:21.040 | and some of those don't have any basis in science,

00:02:24.420 | there are phototherapies that do have

00:02:27.320 | a strong foundation in quality science,

00:02:29.480 | and those are the studies and the protocols

00:02:31.480 | that we are going to discuss today.

00:02:33.240 | But I thought that people might appreciate

00:02:35.100 | knowing that over 100 years ago,

00:02:37.400 | people were thinking about the use of light

00:02:39.160 | for the treatment of various diseases

00:02:40.640 | and for improving health,

00:02:41.780 | and indeed, many of those therapies are used today

00:02:45.080 | in high quality hospitals and research institutions,

00:02:48.440 | and of course, clinics and homes around the world.

00:02:51.100 | One of the more exciting examples of phototherapy

00:02:53.220 | in the last few years is the beautiful work

00:02:55.420 | of Dr. Glenn Jeffrey at University College London.

00:02:58.240 | The Jeffrey Lab is known for doing pioneering

00:03:00.260 | and very rigorous research

00:03:01.360 | in the realm of visual neuroscience.

00:03:03.360 | And in the last decade or so,

00:03:04.680 | they turned their attention to exploring the role

00:03:06.960 | of red light therapy for offsetting age-related vision loss.

00:03:11.740 | What they discovered is that just brief exposures

00:03:15.060 | to red light early in the day

00:03:16.960 | can offset much of the vision loss

00:03:18.920 | that occurs in people 40 years or older.

00:03:21.840 | And what's remarkable about these studies

00:03:23.780 | is that the entire duration of the therapy

00:03:26.560 | is just one to three minutes done

00:03:28.320 | just a few times per week.

00:03:30.080 | What's even more exciting

00:03:31.360 | is that they understand the mechanism by which this occurred.

00:03:34.960 | The cells in the back of the eye

00:03:36.260 | that convert light information into electrical signals

00:03:39.180 | that the rest of the brain can understand

00:03:41.000 | and create visual images from,

00:03:42.800 | well, those cells are extremely metabolically active.

00:03:46.000 | They need a lot of ATP or energy.

00:03:49.840 | And as we age, those cells get less efficient

00:03:53.520 | at creating that ATP and energy.

00:03:56.320 | Exposure to red light early in the day,

00:03:58.960 | and it does have to be early in the day,

00:04:01.060 | allowed those cells to replenish the mechanisms

00:04:03.900 | by which they create ATP.

00:04:05.960 | I'll talk about these experiments

00:04:07.660 | in more detail later in the episode and the protocols

00:04:10.520 | so that you can apply those protocols should you choose.

00:04:13.080 | But I use this as an example of our growing understanding

00:04:17.720 | of not just that phototherapies work, but how they work.

00:04:22.000 | And it is through the linking of protocols and mechanism

00:04:25.840 | that we, meaning all of us,

00:04:28.100 | can start to apply phototherapies

00:04:29.600 | in a rational, safe, and powerful way.

00:04:32.400 | I'm pleased to announce

00:04:33.240 | that I'm hosting two live events this May.

00:04:36.080 | The first live event will be hosted

00:04:37.600 | in Seattle, Washington on May 17th.

00:04:40.280 | The second live event will be hosted

00:04:41.880 | in Portland, Oregon on May 18th.

00:04:44.280 | Both are part of a lecture series

00:04:45.760 | entitled The Brain-Body Contract,

00:04:47.880 | during which I will discuss science

00:04:49.600 | and science-based tools for mental health,

00:04:51.760 | physical health, and performance.

00:04:53.560 | And I should point out that while some of the material

00:04:55.980 | I'll cover will overlap with information covered here

00:04:58.640 | on the Huberman Lab podcast

00:05:00.280 | and on various social media posts,

00:05:02.120 | most of the information I will cover is going to be distinct

00:05:05.280 | from information covered on the podcast or elsewhere.

00:05:08.160 | So once again, it's Seattle on May 17th,

00:05:10.680 | Portland on May 18th.

00:05:12.040 | You can access tickets by going to Hubermanlab.com/tour,

00:05:16.120 | and I hope to see you there.

00:05:17.600 | Before we begin, I'd like to emphasize

00:05:19.280 | that this podcast is separate

00:05:20.660 | from my teaching and research roles at Stanford.

00:05:22.980 | It is, however, part of my desire and effort

00:05:25.080 | to bring zero-cost-to-consumer information about science

00:05:27.760 | and science-related tools to the general public.

00:05:30.480 | In keeping with that theme,

00:05:31.620 | I'd like to thank the sponsors of today's podcast.

00:05:34.400 | Our first sponsor is Athletic Greens, also called AG1.

00:05:38.300 | I started taking AG1 way back in 2012,

00:05:41.240 | so I'm delighted that they're sponsoring the podcast.

00:05:43.680 | The reason I started taking AG1

00:05:45.340 | and the reason I still take AG1 once or twice a day

00:05:48.400 | is that it covers my foundational vitamin,

00:05:50.660 | mineral, and probiotic needs.

00:05:52.520 | It also has adaptogens and things like zinc

00:05:54.960 | for immune system function,

00:05:56.680 | but the probiotics are one of the key features in there.

00:05:59.440 | I've done several podcasts on the gut microbiome,

00:06:01.740 | which are these trillions of microbiota

00:06:03.600 | that live in our digestive tract

00:06:05.040 | and that are crucial for our immune system,

00:06:07.040 | brain function, and so on.

00:06:09.400 | One way to enhance our gut microbiome

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00:06:12.880 | is to make sure that we get the correct probiotics,

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00:07:15.660 | And personally, I'm not a big fan

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00:09:56.440 | Okay, let's talk about light.

00:09:57.860 | First, I want to talk about the physics of light

00:10:00.460 | and I promise to make that very clear

00:10:01.980 | even if you don't have a background in physics.

00:10:03.740 | And then I want to talk about the biology of light,

00:10:06.620 | meaning how light is converted into signals

00:10:09.680 | that your brain and body can use

00:10:11.860 | to impact things like organ health or disease

00:10:15.260 | or how you can use light in order to repair

00:10:17.960 | particular organs like your skin,

00:10:19.940 | your eyes, your brain, et cetera.

00:10:22.080 | The physics of light can be made very simple

00:10:24.140 | by just illustrating a few key bullet points.

00:10:26.840 | The first bullet point is that

00:10:28.640 | light is electromagnetic energy.

00:10:31.720 | If the word electromagnetic feels daunting to you,

00:10:34.640 | well then just discard that

00:10:35.860 | and just think of light as energy

00:10:37.640 | and think of energy as something that can impact

00:10:41.220 | other things in its environment.

00:10:43.700 | Now, the way to imagine light

00:10:46.080 | or to conceptualize light as energy

00:10:48.380 | is that all around you,

00:10:49.620 | light is traveling in these little wavelengths.

00:10:51.580 | And the reason for those of you that are watching,

00:10:53.200 | I'm making a little wavy motion with my hand

00:10:55.000 | is that's actually the way that light energy moves

00:10:56.900 | in little waves,

00:10:58.020 | just like sound waves are coming at you

00:10:59.740 | and impinging on your ears.

00:11:01.000 | If you can hear me talking right now, that is happening.

00:11:03.260 | Those are sound waves,

00:11:04.100 | meaning the movement of air particles out there

00:11:07.020 | impacting your eardrum.

00:11:08.180 | Well, light energy is just little bits

00:11:10.740 | of electromagnetic energy traveling

00:11:13.100 | through your environment all the time in these little waves

00:11:16.740 | and impinging on your brain and body and eyes, et cetera.

00:11:20.740 | And as I mentioned before,

00:11:22.180 | energy can change the way that other things behave.

00:11:25.740 | It can cause reactions in cells of your body.

00:11:29.180 | It can cause reactions in fruit, for instance, right?

00:11:32.000 | You see a piece of fruit and it's not ripe,

00:11:34.320 | but it gets a lot of sunlight and it ripens.

00:11:36.000 | That's because the electromagnetic energy of sunlight

00:11:39.260 | had an impact on that plant or that tree,

00:11:42.360 | or even on the fruit directly.

00:11:44.280 | As a parallel example of energy

00:11:46.180 | and its ability to impact other things,

00:11:49.380 | we are all familiar with food

00:11:50.760 | and the fact that food has calories.

00:11:52.800 | Calorie is a measure of energy.

00:11:55.420 | It has everything to do with how much heat is generated

00:11:58.500 | when you burn a particular article of food,

00:12:00.800 | believe it or not.

00:12:01.840 | And it turns out that how hot a given article of food burns

00:12:06.680 | gives you a sense of how much energy

00:12:08.320 | it can provide your body in terms of your body's ability

00:12:11.560 | to store or use that energy.

00:12:13.920 | So again, think of light as electromagnetic energy,

00:12:16.860 | but really put that word energy into capital letters,

00:12:20.980 | embed that in your mind going forward,

00:12:22.900 | and you'll understand most of the first bullet point

00:12:26.560 | of what light is in terms of the physics of light.

00:12:29.860 | Now, the second thing that you need to understand

00:12:31.860 | about the physics of light

00:12:33.100 | is that light has many different wavelengths.

00:12:35.740 | And the simplest way to conceptualize this

00:12:37.620 | is to imagine that cover of that Pink Floyd album

00:12:39.680 | where there's a prism,

00:12:40.760 | you have a white beam of light going into that prism,

00:12:43.660 | and then the prism splits that beam of light

00:12:46.140 | into what looks like a rainbow.

00:12:48.080 | So you've got your red, your orange, your greens,

00:12:49.660 | your blues, your purples, et cetera.

00:12:51.820 | Anytime we have light in our environment

00:12:54.080 | that is so-called white light,

00:12:55.740 | it includes all those wavelengths,

00:12:57.680 | but sunlight and other forms of light

00:13:00.840 | also have other wavelengths of light that we can't see.

00:13:05.020 | So when we think about the rainbow,

00:13:06.380 | that's just the visible spectrum of light.

00:13:09.100 | There are also wavelengths of light

00:13:11.020 | that are not visible to us,

00:13:12.420 | but that are visible to some other animals

00:13:15.280 | and that can still impact your brain and body

00:13:19.140 | because there is still energy at those wavelengths.

00:13:22.920 | I'll give a few examples of this.

00:13:24.940 | Humans are not a species that can see

00:13:27.420 | into the infrared realm of the spectrum.

00:13:31.380 | A pit viper, meaning a snake that has infrared sensors,

00:13:35.960 | however, can sense in the infrared.

00:13:38.900 | So if you were to walk through a jungle

00:13:40.980 | and there's a pit viper there,

00:13:42.640 | it sees you as a cloud of heat emission

00:13:46.340 | because your body is emitting infrared energy all the time.

00:13:51.180 | You're casting off infrared energy.

00:13:53.740 | The snake can see it, you can't.

00:13:55.780 | If you were to put on a particular set of goggles

00:13:58.700 | that were infrared goggles,

00:14:01.220 | well, then you would be able to see the heat emissions

00:14:03.580 | of any organism, human or otherwise,

00:14:06.020 | that could emit infrared energy.

00:14:08.860 | Let's take the opposite end of the spectrum.

00:14:11.940 | We are familiar with seeing things that are blue or green

00:14:14.660 | or very pale blue, but as we say below that,

00:14:18.740 | meaning even shorter wavelength light is out there.

00:14:21.440 | Ultraviolet light is a really good example

00:14:23.960 | of light energy that's coming from the sun

00:14:26.240 | and is in our environment

00:14:27.280 | and is being reflected off surfaces all the time.

00:14:29.720 | We don't see it and yet if it's very bright outside,

00:14:33.400 | that ultraviolet light can burn our skin.

00:14:36.280 | As you'll learn in today's episode,

00:14:38.080 | ultraviolet light can also positively impact us.

00:14:42.760 | In fact, I will describe a particular set of new results

00:14:45.860 | that show that ultraviolet light viewed

00:14:48.640 | for just a few minutes each day

00:14:51.160 | or landing on the skin for just a few minutes each day

00:14:53.560 | can actually offset a lot of pain.

00:14:56.440 | It actually has the ability to reduce the amount of pain

00:14:59.960 | sensed by your body and we now understand

00:15:01.960 | the specific circuits in the brain and body

00:15:03.760 | that allow that to happen.

00:15:05.200 | I'll talk about that

00:15:06.040 | in the related protocols a little bit later.

00:15:08.320 | So the important thing to understand

00:15:09.520 | about the physics of light

00:15:10.840 | is that there's energy at all these different wavelengths.

00:15:13.320 | We only see some of those wavelengths,

00:15:15.600 | which basically is to say that light impacts us

00:15:19.040 | at many different levels.

00:15:21.340 | And the so-called levels that I'm referring to

00:15:24.000 | are the different wavelengths of light.

00:15:26.080 | And you're welcome to think of the different wavelengths

00:15:28.160 | of light as different colors,

00:15:29.720 | but do understand that there are truly colors of light

00:15:33.240 | that you and I can't see and yet that have powerful impact

00:15:37.380 | on your brain and body.

00:15:38.440 | Now, the third bullet point to understand

00:15:40.460 | about the physics of light

00:15:41.880 | is that different wavelengths of light

00:15:44.240 | because of the way that their wave travels

00:15:47.880 | can penetrate tissues to different depths.

00:15:51.800 | This is very, very important.

00:15:53.960 | Today, we're going to talk a lot about red light therapies

00:15:56.400 | and near infrared light therapies.

00:15:59.920 | Those are so-called longer wavelengths.

00:16:02.280 | Longer wavelength, just think of a bigger, longer wave,

00:16:06.360 | a bigger curve, as opposed to short wavelength light,

00:16:08.680 | which is going to be shorter.

00:16:10.780 | A short wavelength light would be something like blue

00:16:12.780 | or green light or ultraviolet light.

00:16:14.720 | Blue, green, and ultraviolet light,

00:16:17.840 | because it's short wavelength light,

00:16:19.640 | doesn't tend to penetrate tissues very easily.

00:16:23.620 | It has to do with the way that the physics of light

00:16:25.520 | interacts with the physical properties of your skin

00:16:27.780 | and other tissues of your body.

00:16:29.200 | But basically, if you were to shine UV light

00:16:31.240 | onto your arm, for instance,

00:16:33.000 | it could impact the skin on the surface of the arm

00:16:35.200 | and maybe some of the cells

00:16:36.880 | just beneath the top layer of skin,

00:16:38.980 | but it wouldn't penetrate much deeper.

00:16:40.880 | Long wavelength light like red light and near infrared light

00:16:45.960 | has this amazing ability to penetrate through tissues,

00:16:49.960 | including your skin.

00:16:51.280 | And so if we were to shine red light

00:16:53.440 | or near infrared light onto your arm,

00:16:56.120 | it would pass through that top layer of skin.

00:16:59.880 | It might impact it a little bit,

00:17:01.460 | but it could penetrate deeper into your skin,

00:17:04.800 | not just to the skin layers,

00:17:05.980 | but maybe even down to the bone,

00:17:07.640 | maybe even down to the bone marrow.

00:17:09.540 | And for many people, this will be hard to conceptualize.

00:17:11.800 | You think, well, wait, I've got a skin there.

00:17:13.360 | Doesn't the light just bounce off?

00:17:14.800 | And the answer is no,

00:17:15.940 | because of the way that long wavelength light

00:17:19.540 | interacts with the absorbance properties of your skin.

00:17:22.520 | Absorbance properties is just the way

00:17:24.040 | that the skin takes light energy

00:17:26.160 | and converts it into a different form of energy.

00:17:29.280 | And your skin is not able to take long wavelength light

00:17:32.780 | like red light and near infrared light and absorb it,

00:17:36.340 | but the tissues deeper in your body can.

00:17:39.640 | So if you shine red light or near infrared light

00:17:42.200 | onto the surface of your skin,

00:17:43.500 | you'll see a red glow there as a reflectance

00:17:46.040 | on the surface of your skin.

00:17:47.440 | But a lot of the photon energy,

00:17:49.720 | the light energy in those longer wavelengths

00:17:52.000 | is indeed passing through those top layers of skin

00:17:54.840 | into the deeper layers of skin

00:17:56.400 | and can even make it into the deep layers of your arm.

00:17:59.640 | And as we start to transition from the physics of light

00:18:01.880 | to the biological impacts of light,

00:18:03.920 | just understanding that the different wavelengths of light

00:18:07.380 | impact our tissues at different levels,

00:18:09.280 | literally at different depths,

00:18:10.920 | will help you better understand

00:18:12.840 | how light of different colors, of different intensities,

00:18:16.200 | and how long you are exposed to those colors

00:18:19.620 | and intensities of light can change the way

00:18:22.320 | that the cells and the organs of your body work.

00:18:25.700 | And if it didn't sound weird enough

00:18:27.040 | that you can pass light through particular tissues

00:18:29.800 | and have them land and be absorbed

00:18:31.740 | at tissues deeper in your body,

00:18:34.480 | well, it turns out that different wavelengths of light

00:18:37.520 | are also best absorbed by particular

00:18:40.920 | so-called organelles within your cells.

00:18:43.520 | What are organelles?

00:18:44.360 | Organelles are the different compartments

00:18:46.240 | and different functions within a given cell.

00:18:48.900 | So for instance, your mitochondria,

00:18:50.420 | which are responsible for generating ATP

00:18:52.520 | and energy in your cells,

00:18:54.920 | those exist at a particular depth,

00:18:56.980 | at a particular location within a cell.

00:18:58.560 | They're not all at the cell surface.

00:18:59.920 | They sit somewhat deeper in the cell.

00:19:01.760 | The nucleus of your individual cells contains DNA,

00:19:05.120 | and that sits at a particular depth

00:19:06.620 | or location within your cell.

00:19:08.120 | Different wavelengths of light

00:19:10.720 | not only can penetrate down into different tissues

00:19:13.480 | and into different cells of your body,

00:19:15.600 | but they can also penetrate and access particular organelles,

00:19:19.540 | meaning mitochondria or the nucleus

00:19:22.180 | or the different aspects of your cells

00:19:24.040 | that are responsible for different functions.

00:19:26.400 | This is exquisitely important and it's exquisitely powerful

00:19:31.340 | because as you'll learn today,

00:19:32.760 | particular wavelengths of light

00:19:34.160 | can be used to stimulate the function of particular organelles

00:19:37.160 | within particular cells

00:19:39.000 | within particular organs of your body.

00:19:41.560 | I can think of no other form of energy,

00:19:43.780 | not sound, not chemical energy, so not drugs,

00:19:47.800 | not food, not touch,

00:19:51.720 | no form of energy that can target the particular locations

00:19:55.720 | in our cells, in our organelles, in our organs,

00:19:59.640 | and in our body to the extent that light can.

00:20:02.400 | In other words, if you had to imagine

00:20:04.660 | a real-world surgical tool by which to modulate our biology,

00:20:09.660 | light would be the sharpest

00:20:11.640 | and the most precise of those tools.

00:20:13.840 | Now let's talk about how light is converted

00:20:15.280 | into biological signals.

00:20:17.040 | There are several ways in which that is accomplished,

00:20:19.600 | but the fundamental thing to understand

00:20:22.200 | is this notion of absorption of light energy.

00:20:26.020 | Certain pigments or colors

00:20:30.440 | in the thing that is receiving the light energy,

00:20:33.800 | meaning the thing that the light energy lands on

00:20:37.360 | are going to absorb particular wavelengths of light.

00:20:40.480 | Now, I promise you that you already intuitively know

00:20:43.320 | how this works.

00:20:44.700 | For instance, if you were to sit outside

00:20:47.280 | on a very bright sunny day

00:20:49.080 | and you had a table in front of you that was metal,

00:20:52.520 | you might find it hard to look down at that metal table

00:20:55.000 | because it's reflecting a lot of light

00:20:56.900 | of particular wavelengths.

00:20:58.200 | If that table were pitch black, however,

00:21:02.000 | it wouldn't reflect quite as much

00:21:04.520 | and you would be able to comfortably look at it.

00:21:06.880 | If that table were red, it might be somewhere in between.

00:21:10.860 | If that table were green,

00:21:12.820 | it would be also somewhere in between,

00:21:14.700 | but let's say it were very light blue,

00:21:16.520 | well, then it might reflect almost as much as a table

00:21:19.720 | that were just metal or a white table surface.

00:21:23.400 | So the absorbance properties of a given surface

00:21:26.420 | will determine whether or not light energy goes

00:21:28.600 | and stays at that location

00:21:31.080 | and has an impact on that location,

00:21:33.280 | or whether or not it bounces off.

00:21:35.220 | Every biological function of light

00:21:38.720 | has to do with the absorbance or the reflectance of light

00:21:43.040 | or light passing through that particular thing,

00:21:46.780 | meaning that particular cell or compartment within a cell.

00:21:49.960 | I'd like to make it clear how this works

00:21:53.520 | by using the three primary examples

00:21:55.840 | of how you take light in your environment

00:21:58.920 | and convert it into biological events.

00:22:01.620 | We have photoreceptors in the back of our eyes.

00:22:05.960 | These photoreceptors come in two major types,

00:22:08.680 | the so-called rods and the cones.

00:22:10.340 | The rods are very elongated, they look like rods,

00:22:13.260 | and the cones look like little triangles.

00:22:15.980 | Rods and cones have within them photopigment.

00:22:20.800 | They have dark stuff that's stacked up in little layers.

00:22:24.300 | Rods absorb light of essentially any wavelength.

00:22:27.380 | There's some variation to that,

00:22:28.720 | but let's just say rods don't care

00:22:32.020 | about the different colors of light.

00:22:34.900 | They will absorb light energy, photon energy,

00:22:37.700 | if it's red, if it's green, if it's blue, if it's yellow,

00:22:41.320 | doesn't matter as long as that light is bright enough.

00:22:44.160 | And it turns out that rods are very, very sensitive.

00:22:46.480 | They can detect very, very small numbers of photons.

00:22:50.760 | And rods are essentially what you use

00:22:53.140 | to see in very low light conditions.

00:22:55.400 | We'll return more to vision later.

00:22:57.440 | The cones come in three major varieties,

00:23:00.920 | at least for most people who aren't colorblind,

00:23:02.960 | you have so-called red cones, green cones, and blue cones,

00:23:05.300 | but they're not really red, green, and blue

00:23:06.800 | in the back of your eye.

00:23:07.900 | They are cones that either absorb long wavelength light,

00:23:11.680 | red, that absorb medium wavelength light, green,

00:23:16.080 | or short wavelength light, blue.

00:23:18.160 | The reason that they can absorb different wavelengths

00:23:22.280 | of light is they have different photopigments.

00:23:24.740 | So much as the example I gave before,

00:23:26.920 | where you have different tables outside

00:23:29.580 | in the sunny environment,

00:23:30.760 | and some are reflecting light more than others,

00:23:32.660 | others are absorbing light more than others.

00:23:35.460 | Well, so too the photoreceptors,

00:23:38.120 | meaning the cones are absorbing light

00:23:41.280 | of different wavelengths to different extents.

00:23:43.720 | And in a absolutely incredible way,

00:23:46.560 | your brain is actually able to take that information

00:23:49.000 | and create this perception that we have of color.

00:23:51.360 | But that's another story altogether

00:23:52.840 | that we'll just touch on a little bit more later,

00:23:55.500 | but that if you want to learn all about,

00:23:57.040 | you can go to our episode on vision.

00:23:59.840 | So that's photoreceptors in the back of your eye

00:24:03.760 | absorbing light of different wavelengths, rods and cones.

00:24:07.100 | The other place, of course,

00:24:08.180 | where light can impact our body is on our surface,

00:24:11.180 | on our skin.

00:24:12.620 | And skin has pigment too.

00:24:14.640 | We call that pigment melanin.

00:24:16.960 | We have within our skin multiple cell types,

00:24:19.840 | but in the top layer of skin,

00:24:21.180 | which is called the epidermis,

00:24:23.060 | we have keratinocytes and we have melanocytes.

00:24:27.340 | And the melanocytes are the cells

00:24:29.700 | that create pigmentation of the skin.

00:24:31.340 | And of course, there is wide variation in the degree

00:24:34.760 | to which there's pigmentation of the skin,

00:24:37.160 | which has to do with genetics,

00:24:38.580 | also has to do with where you were born and raised,

00:24:41.100 | how much light exposure you have throughout the year, right?

00:24:43.720 | So people toward the equator

00:24:45.000 | tend to have more melanocyte activity

00:24:46.900 | than people who are located at the North Pole.

00:24:49.380 | And of course, people live at different locations

00:24:51.260 | throughout the earth,

00:24:52.100 | regardless of their genetic background

00:24:53.920 | or where they were born.

00:24:54.860 | And so, as you all know, with light exposure,

00:24:58.380 | those melanocytes will turn on genetic programs

00:25:02.560 | and other biological programs

00:25:04.360 | that lead to enhanced pigmentation on the skin,

00:25:06.720 | which we call tanning.

00:25:08.720 | The way they do that is by absorbing UV light specifically.

00:25:12.700 | So with melanocytes, we have a very specific example

00:25:16.580 | of how a pigment absorbs light of a particular length,

00:25:20.300 | in this case, ultraviolet short wavelength light,

00:25:23.200 | which in turn creates a set of biological signals

00:25:26.860 | within those cells

00:25:27.840 | that in turn creates changes in our skin pigmentation.

00:25:31.000 | So we have photoreceptors, we have melanocytes.

00:25:33.200 | And the third example I'd like to provide

00:25:35.240 | is that of every cell of your body.

00:25:37.640 | And what I mean by that is that every cell of your body,

00:25:40.360 | meaning a cell that is part of your bone tissue

00:25:44.540 | or your bone marrow or heart tissue or liver or spleen,

00:25:48.760 | if light can access those cells,

00:25:51.520 | it will change the way that those cells function

00:25:53.780 | for better or for worse.

00:25:56.520 | For many organs within our body

00:25:58.640 | that reside deep to our skin,

00:26:02.060 | light never arrives at those cells.

00:26:05.320 | A really good example of this that we'll touch on later

00:26:07.600 | is the spleen.

00:26:09.400 | Unless you have massive damage to your body surface,

00:26:12.560 | unless you literally have a hole in your body,

00:26:14.760 | light will never land directly on your spleen.

00:26:18.060 | But the spleen still responds to light information

00:26:21.760 | through indirect pathways.

00:26:24.120 | And those indirect pathways arise through light

00:26:26.920 | arriving on the skin and light arriving on the eyes.

00:26:30.600 | So a key principle that I'm going to return to

00:26:32.740 | again and again today is that the ways in which light

00:26:37.200 | can impact the biology of your organelles, your cells,

00:26:40.600 | your organs and the tissues and indeed your whole body

00:26:43.500 | can either be direct.

00:26:45.360 | So for instance, light onto your skin impacting skin

00:26:48.240 | or light onto your photoreceptors

00:26:49.780 | impacting the photoreceptors of your eye.

00:26:52.060 | Or it can be indirect.

00:26:53.880 | It can be light arriving on your photoreceptors,

00:26:56.920 | the photoreceptors then informing another cell type

00:26:59.880 | which informs another cell type,

00:27:01.720 | which then relays a signal in kind of a bucket brigade

00:27:04.880 | manner off to the spleen and says to the spleen,

00:27:07.620 | hey, there's a lot of UV light out here.

00:27:10.360 | We're actually under stress.

00:27:12.080 | In fact, there's so much UV light

00:27:13.680 | that you need to activate an immune program

00:27:16.720 | to protect the skin.

00:27:18.080 | And in response to that,

00:27:19.160 | the spleen can deploy certain signals and certain cell types

00:27:21.920 | to go out and start repairing skin that's being damaged

00:27:24.380 | by UV light.

00:27:25.400 | So we have direct signals and we have indirect signals,

00:27:28.360 | but in every case,

00:27:30.960 | it starts with light of particular wavelengths

00:27:34.260 | being absorbed by particular pigments or properties

00:27:37.880 | of the surfaces that those light waves land on.

00:27:42.300 | And as you recall from our discussion

00:27:43.840 | about the physics of light,

00:27:45.060 | remember it's not just about light impinging

00:27:47.460 | on the surface of your body.

00:27:48.560 | Light can actually penetrate deep to the skin

00:27:51.920 | and access at least certain tissues and cells of your body.

00:27:55.800 | Even though you can't see those wavelengths of light,

00:27:58.400 | they are getting into you all the time.

00:28:00.980 | So perhaps the best way to wrap this discussion

00:28:04.080 | about the physics and the biology of light

00:28:06.120 | with a bit of a bow

00:28:07.800 | is to think about light as a transducer,

00:28:11.240 | meaning a communicator of what's going on

00:28:13.880 | in the environment around you.

00:28:15.720 | And that some of those signals are arriving at the surface

00:28:19.120 | and impacting the surface of your body.

00:28:21.220 | But many of those signals are being taken by cells

00:28:24.060 | at the surface of your body,

00:28:25.800 | meaning your melanocytes in your skin

00:28:27.520 | and the photoreceptors of your eyes,

00:28:29.280 | and then being passed off as a set of instructions

00:28:33.320 | to the other organs and tissues of your body.

00:28:35.720 | Light can impact our biology in very fast,

00:28:38.920 | moderately fast and slow ways.

00:28:41.480 | But even the slow ways in which light can impact our biology

00:28:45.180 | can be very powerful and very long lasting.

00:28:48.340 | Just as a quick example of the rapid effects of light

00:28:52.120 | on our biology.

00:28:53.920 | If you were to go from a room that is dimly lit or dark

00:28:58.320 | into a very brightly lit room,

00:29:01.060 | you would immediately feel very alert.

00:29:04.560 | You might say, no, that's not true.

00:29:05.960 | Sometimes I wake up and it's dark and I kind of stumble out

00:29:09.040 | and it's lighter out in the next room

00:29:10.980 | and it takes me a while to wake up.

00:29:12.500 | Ah, but if we were to move you from a room

00:29:15.040 | that was very dark to very bright,

00:29:17.060 | a signal conveyed from your eyes

00:29:19.840 | to an area of your brainstem called the locus coeruleus

00:29:23.140 | would cause the release of adrenaline

00:29:25.740 | similar to the release of adrenaline

00:29:27.480 | if you were to be dropped into very, very cold water

00:29:29.980 | all of a sudden.

00:29:30.820 | You just had an immediate wake up signal

00:29:32.360 | to your brain and body.

00:29:33.500 | So that's an example of a rapid effect of light

00:29:36.420 | on your biology.

00:29:37.500 | Not a very typical one, but nonetheless,

00:29:39.720 | one that has a hardwired biological mechanism.

00:29:43.500 | At the other end of the spectrum

00:29:45.520 | are what we call slow integrating effects of light

00:29:48.460 | on our biology.

00:29:49.940 | So what I mean by that are ways in which

00:29:52.720 | your body is taking information about light

00:29:55.260 | in the environment, not in the sort of snapshot acute sense,

00:29:59.720 | but averaging the amount of light in your environment.

00:30:02.500 | And that average light information

00:30:05.240 | is changing the way that your biology works.

00:30:07.940 | But even though this is a slow process,

00:30:10.620 | as I mentioned before, it's a very powerful one.

00:30:13.460 | The primary example of this

00:30:15.500 | are so-called circannual rhythms.

00:30:18.300 | Circannual rhythms are literally a calendar

00:30:21.820 | that exists within your body that uses not numbers,

00:30:26.420 | but amounts of hormone that are released

00:30:28.820 | into your brain and body each day and each night

00:30:31.820 | as a way of knowing where you are

00:30:34.100 | in the 365 day calendar year.

00:30:37.520 | Now that might seem kind of crazy, but it's not crazy.

00:30:40.900 | The earth travels around the sun once every 365 days.

00:30:45.020 | And depending on where you are on the earth,

00:30:48.220 | where you live, you are going to get more or less light

00:30:53.020 | each day on average, depending on the time of year.

00:30:56.520 | So if you're in the Northern hemisphere

00:30:58.800 | in the winter months, days are shorter, nights are longer.

00:31:02.900 | In the summer months, days are longer, nights are shorter.

00:31:05.980 | And of course, things change whether or not

00:31:08.340 | you're in the Northern hemisphere

00:31:10.060 | or the Southern hemisphere.

00:31:11.660 | But nonetheless, in short days,

00:31:15.140 | you have more darkness, that's obvious.

00:31:17.840 | And if you understand that light arriving on the eyes

00:31:22.660 | is absorbed by a particular cell type

00:31:26.140 | called the intrinsically photosensitive ganglion cell,

00:31:29.020 | it's just a name, you don't need to know the name,

00:31:30.620 | but if you want, it's the so-called

00:31:31.740 | intrinsically photosensitive ganglion cell,

00:31:33.420 | also called the melanopsin cell,

00:31:35.280 | because it contains an opsin, a photopigment

00:31:38.600 | that absorbs short wavelength light

00:31:41.920 | that arrives through sunlight,

00:31:43.700 | those cells communicate to particular stations in the brain

00:31:47.460 | that in turn connect to your so-called pineal gland,

00:31:51.640 | which is this little pea-sized gland

00:31:53.400 | in the middle of your brain

00:31:54.660 | that releases a hormone called melatonin.

00:31:57.600 | And the only thing you need to know

00:31:59.060 | is that light activates these particular cells,

00:32:02.160 | the intrinsically photosensitive melanopsin cells,

00:32:04.500 | which in turn shuts down the production of melatonin

00:32:08.420 | from the pineal gland.

00:32:09.640 | If you think about this in terms of the travel of the earth

00:32:14.480 | around the sun across the year,

00:32:16.940 | what it means is that in short days,

00:32:19.560 | because there's very little light on average

00:32:22.040 | landing on these cells,

00:32:23.700 | the duration of melatonin release will be much longer

00:32:28.140 | because as I mentioned before,

00:32:29.620 | light inhibits, it shuts down melatonin.

00:32:32.540 | Whereas in the summer months,

00:32:34.340 | much more light on average will land on your eyes, right?

00:32:37.540 | Because days are longer,

00:32:38.960 | even if you're spending more time indoors,

00:32:40.420 | on average, you're going to get more light

00:32:43.500 | to activate these cells.

00:32:45.140 | And because light shuts down melatonin production,

00:32:48.600 | what you'll find is that the duration of melatonin release

00:32:51.280 | for the pineal is much shorter.

00:32:54.380 | So melatonin is a transducer.

00:32:57.460 | It's a communicator of how much light on average

00:33:00.580 | is in your physical environment.

00:33:02.960 | What this means is for people living

00:33:05.820 | in the Northern hemisphere,

00:33:07.420 | you're getting more melatonin release in the winter months

00:33:10.540 | than you are in the summer months.

00:33:12.640 | So you have a calendar system that is based in a hormone,

00:33:17.640 | and that hormone is using light in order to determine

00:33:22.420 | where you are in that journey around the sun.

00:33:26.160 | Now, this is beautiful, at least to me, it's beautiful,

00:33:28.500 | because what it means is that the environment around us

00:33:31.860 | is converted into a signal

00:33:33.820 | that changes the environment within us.

00:33:36.860 | That signal is melatonin.

00:33:38.780 | And melatonin is well-known for its role

00:33:41.180 | in making us sleepy each night

00:33:42.860 | and allowing us to fall asleep.

00:33:44.780 | Many of you have probably heard before,

00:33:46.200 | I am not a big fan of melatonin supplementation

00:33:48.900 | for a number of reasons, but just as a quick aside,

00:33:52.160 | the levels of melatonin that are in most supplements

00:33:54.340 | are far too high to really be considered physiological.

00:33:57.480 | They are indeed super physiological in most cases,

00:34:00.180 | and melatonin can have a number of different effects,

00:34:02.920 | not just related to sleep,

00:34:05.140 | but that's supplemented melatonin.

00:34:07.680 | Here, I'm talking about our natural production

00:34:10.360 | and release of melatonin,

00:34:11.460 | according to where we are in the 365-day calendar year.

00:34:15.740 | Endogenous melatonin,

00:34:18.220 | meaning the melatonin that we make within our bodies

00:34:20.380 | naturally, not melatonin that's supplemented,

00:34:23.560 | has two general categories of effects.

00:34:26.760 | The first set of effects are so-called regulatory effects,

00:34:29.140 | and the others are protective effects.

00:34:30.900 | The regulatory effects are, for instance,

00:34:32.780 | that melatonin can positively impact bone mass.

00:34:37.540 | So melatonin can, for instance,

00:34:39.300 | turn on the production of osteoblasts,

00:34:41.800 | which are essentially stem cells that make more bone for us,

00:34:45.820 | that make our bones stronger,

00:34:47.420 | and that can replace damaged aspects of our bone.

00:34:50.040 | Melatonin is also involved in maturation of the gonads

00:34:53.940 | during puberty, the ovaries, and the testes.

00:34:56.860 | Although there, the effects of melatonin

00:34:58.620 | tend to be suppressive on maturation

00:35:01.300 | of the ovaries and testes,

00:35:02.780 | meaning high levels of melatonin

00:35:04.620 | tend to reduce testicle volume

00:35:07.520 | and reduce certain functions within the testes,

00:35:10.880 | including sperm production and testosterone production.

00:35:13.580 | And within the ovaries,

00:35:15.420 | melatonin can suppress the maturation of eggs, et cetera.

00:35:18.580 | Now, I don't want anyone to get scared

00:35:20.020 | if you've been taking melatonin.

00:35:21.540 | Most of the effects of melatonin on those functions

00:35:23.880 | are reversible,

00:35:25.180 | but I should point out that one of the reasons

00:35:27.260 | why children don't go into puberty until a particular age

00:35:30.660 | is that young children tend to have

00:35:32.540 | chronically high endogenous melatonin,

00:35:34.760 | and that is healthy to keep them out of puberty

00:35:37.380 | until it's the right time for puberty to happen.

00:35:40.700 | So melatonin can increase bone mass,

00:35:43.400 | but reduces gonad mass, so to speak.

00:35:46.860 | It's going to have varying effects

00:35:48.740 | depending on the ratios and levels of other hormones

00:35:51.460 | and other biological events in the body.

00:35:53.220 | But as you can see,

00:35:54.140 | melatonin has these powerful regulatory effects

00:35:56.500 | on other tissues.

00:35:57.540 | I should also mention that melatonin

00:35:59.140 | is a powerful modulator of placental development.

00:36:02.120 | So for anyone that's pregnant,

00:36:03.500 | if you're considering melatonin supplementation,

00:36:05.860 | please, please, please talk to your OBGYN,

00:36:08.540 | talk to your other doctor as well.

00:36:10.980 | You want to be very, very cautious

00:36:12.380 | because of the powerful effects that melatonin can have

00:36:14.660 | on the developing fetus and placenta.

00:36:16.900 | For people that are not pregnant,

00:36:19.080 | in fact, all people,

00:36:20.020 | melatonin has a powerful effect

00:36:22.660 | on the central nervous system as a whole.

00:36:24.960 | Your brain and spinal cord are the major components

00:36:26.980 | of your central nervous system,

00:36:28.460 | and melatonin, because it's associated with darkness,

00:36:32.180 | which is just another way of saying

00:36:34.200 | that light suppresses melatonin,

00:36:35.880 | melatonin is thereby associated with the dark phase

00:36:39.180 | of each 24 hour cycle,

00:36:40.660 | it can have a number of different effects

00:36:44.700 | in terms of waking up or making our body feel more sleepy.

00:36:48.340 | And it does that by way of impacting cells

00:36:50.420 | within our nervous system,

00:36:51.460 | literally turning on certain brain areas,

00:36:54.040 | turning off other brain areas.

00:36:55.580 | And it does that through a whole cascade

00:36:57.060 | of biological mechanisms,

00:36:58.460 | a bit too detailed to get into today.

00:37:00.460 | So melatonin is regulating how awake or asleep we are.

00:37:03.000 | It tends to make us more asleep, incidentally.

00:37:05.940 | It's regulating our timing of puberty

00:37:08.860 | and it's regulating how our gonads,

00:37:11.300 | the testes and ovaries function,

00:37:12.900 | even in adulthood to some extent,

00:37:14.780 | and it's regulating bone mass.

00:37:17.420 | As I mentioned before,

00:37:18.240 | melatonin also has protective effects.

00:37:20.480 | It can activate our immune system.

00:37:22.140 | It is among the most potent antioxidants.

00:37:25.500 | So it is known to have certain anti-cancer properties

00:37:28.140 | and things of that sort,

00:37:29.620 | which is not to say that you simply want more melatonin.

00:37:32.120 | I think a lot of people get misled

00:37:33.860 | when they hear something like melatonin

00:37:36.100 | has anti-cancer properties.

00:37:37.960 | That doesn't mean that just cranking up

00:37:39.580 | the levels of melatonin by supplementing it,

00:37:42.060 | or by spending time in darkness and not getting any light,

00:37:44.540 | which would of course inhibit melatonin

00:37:46.140 | is going to be beneficial for combating cancer.

00:37:48.500 | That's not the way it works.

00:37:50.540 | It is actually the rise and fall of melatonin

00:37:53.980 | every 24 hour cycle,

00:37:55.660 | and the changes in the duration of that melatonin signal

00:37:58.480 | throughout the seasons that has these anti-cancer

00:38:01.780 | and antioxidant effects.

00:38:03.300 | So when we think about light impacting our biology,

00:38:07.100 | the reason I bring up melatonin

00:38:08.660 | as the primary example of that is A,

00:38:10.740 | because melatonin impacts so many important functions

00:38:13.220 | within our brain and body,

00:38:14.420 | but also because hormones in general, not always,

00:38:17.840 | but in general are responsible

00:38:19.220 | for these slow modulatory effects on our biology.

00:38:22.660 | And so I'm using this as an example

00:38:24.780 | of how light throughout the year

00:38:26.740 | is changing the way that the different cells and tissues

00:38:29.660 | and organs of your body are working,

00:38:31.060 | and that melatonin is the transducer of that signal.

00:38:34.300 | So at this point,

00:38:35.140 | we can say light powerfully modulates melatonin,

00:38:38.060 | meaning it shuts down melatonin.

00:38:39.700 | Melatonin is both beneficial for certain tissues

00:38:42.420 | and suppressive for other tissues and functions.

00:38:46.220 | What should we do with this information?

00:38:47.780 | Well, it's very well established now

00:38:50.860 | that one of the best things that we can all do

00:38:53.100 | is to get the proper amount of sunlight each day.

00:38:56.580 | And by proper, I mean appropriate for that time of year.

00:39:00.340 | So in the summer months where the days are longer

00:39:03.540 | and nights are shorter,

00:39:04.780 | we would all do well to get more sunlight in our eyes.

00:39:08.220 | And again, it's going to be to our eyes

00:39:10.100 | because as you recall, the pineal sits deep in the brain

00:39:14.220 | and light can't access the pineal directly,

00:39:16.320 | at least not in humans.

00:39:17.820 | So in order to get light information to the pineal

00:39:22.620 | and thereby get the proper levels of melatonin,

00:39:25.240 | according to the time of year,

00:39:27.560 | we should all try and get outside as much as possible

00:39:30.900 | during the long days of summer and spring.

00:39:34.140 | And in the winter months,

00:39:35.340 | it makes sense to spend more time indoors.

00:39:37.720 | For those of you that suffer

00:39:38.820 | from seasonal affective disorder,

00:39:40.180 | which is a seasonal depression

00:39:41.460 | or feel low during the fall and winter months,

00:39:44.180 | there are ways to offset this.

00:39:45.300 | We did an entire episode on mood and circadian rhythms

00:39:47.880 | where we described this.

00:39:49.100 | So it does make sense for some people

00:39:50.480 | to get more bright light in their eyes early in the morning

00:39:52.920 | and throughout the day during the winter months as well.

00:39:56.020 | But nonetheless, changes in melatonin,

00:39:59.380 | meaning changes in the duration of melatonin release

00:40:02.060 | across the year are normal and healthy.

00:40:04.100 | So provided that you're not suffering from depression,

00:40:06.760 | it's going to be healthy to somewhat modulate your amount

00:40:09.540 | of indoor and outdoor time across the year.

00:40:12.260 | The other thing to understand

00:40:13.240 | is this very firmly established fact,

00:40:15.040 | which is light powerfully inhibits melatonin.

00:40:18.140 | If you wake up in the middle of the night

00:40:20.960 | and you go into the bathroom and you flip on the lights,

00:40:23.320 | and those are very bright overhead fluorescent lights,

00:40:26.480 | your melatonin levels,

00:40:28.040 | which would ordinarily be quite high

00:40:30.160 | in the middle of the night,

00:40:31.000 | because you've been eyes closed in the dark presumably,

00:40:33.820 | will immediately plummet to near zero or zero.

00:40:37.000 | We would all do well regardless of time of year

00:40:40.020 | to not destroy our melatonin

00:40:43.540 | in the middle of the night in this way.

00:40:45.380 | So if you need to get up in the middle of the night

00:40:46.940 | and you use the restroom,

00:40:47.780 | which is a perfectly normal behavior for many people,

00:40:50.860 | use the minimum amount of light required

00:40:53.940 | in order to safely move through the environment

00:40:57.080 | that you need to move through.

00:40:58.580 | Melatonin needs to come on early in the night.

00:41:02.440 | It actually starts rising in the evening and towards sleep.

00:41:06.280 | But then as you close your eyes and you go to sleep,

00:41:08.200 | melatonin levels are going to continue to rise

00:41:10.680 | at least for several hours into the night.

00:41:13.580 | Again, if you get up in the middle of the night,

00:41:15.200 | really try hard not to flip on a lot of bright lights.

00:41:17.920 | If you do that every once in a while,

00:41:19.480 | it's not going to be a problem.

00:41:21.000 | But if you're doing that night after night,

00:41:22.960 | you are really disrupting this fundamental signal

00:41:27.440 | that occurs every night,

00:41:28.980 | regardless of winter, spring, summer, et cetera,

00:41:31.280 | and that is communicating information

00:41:33.480 | about where your brain and body should be in time.

00:41:37.040 | And I know that's a little bit of a tricky concept,

00:41:38.900 | but really our body is not meant to function

00:41:41.840 | in the same way during the winter months

00:41:43.320 | as the summer months.

00:41:44.520 | There are functions that are specifically optimal

00:41:48.000 | for the shorter days of winter,

00:41:49.620 | and there are functions that are specifically optimal

00:41:51.800 | for the longer days of summer.

00:41:53.800 | So again, try to avoid bright light exposure to your eyes

00:41:58.520 | in the middle of the night.

00:41:59.560 | And for those of you that are doing shift work,

00:42:01.560 | what I can say is try and avoid getting bright light

00:42:04.100 | in your eyes in the middle of your sleep cycle.

00:42:06.060 | So even if you're sleeping in the middle of the day,

00:42:07.440 | because you have to work at night,

00:42:08.720 | if you wake up during that bout of sleep,

00:42:11.160 | really try hard to limit the amount of light,

00:42:13.360 | which is going to be harder for shift workers, right?

00:42:15.580 | Because there are generally a lot more lights on

00:42:17.420 | and bright lights outside too.

00:42:18.640 | You would want to close the blinds

00:42:20.080 | and limit artificial light inside.

00:42:22.400 | One way to bypass some of the inhibitory effects of light

00:42:26.260 | on melatonin is to change your physical environment

00:42:29.980 | by, for instance, dimming the lights.

00:42:32.000 | That's one simple way, very low cost way.

00:42:34.000 | In fact, you'll save money by dimming the lights

00:42:35.760 | or turning them off.

00:42:36.700 | The other is if you are going to use light

00:42:39.120 | using long wavelength light,

00:42:40.700 | because as you recall,

00:42:41.840 | these intrinsically photosensitive melanopsin cells

00:42:44.040 | within your retina that convey the signal

00:42:46.740 | about bright light in your environment to impact melatonin,

00:42:50.420 | to shut down melatonin,

00:42:51.740 | respond to short wavelengths of light.

00:42:53.840 | So red light is long wavelength light.

00:42:55.880 | You now understand that from our discussion

00:42:57.760 | about the physics of light.

00:42:59.620 | And if you were to use amber colored light or red light,

00:43:03.400 | and even better dim amber or dim red light

00:43:06.680 | in the middle of the night,

00:43:07.520 | well, then you would probably not reduce melatonin at all,

00:43:11.100 | unless those red lights and amber lights

00:43:13.040 | are very, very bright.

00:43:14.080 | Any light, provided it's bright enough,

00:43:16.260 | will shut down melatonin production.

00:43:18.860 | One final point about melatonin,

00:43:20.900 | and this relates to melatonin supplementation as well,

00:43:23.960 | is that now that you understand how potently melatonin

00:43:27.340 | can impact things like cardiovascular function,

00:43:29.220 | immune function, anticancer properties,

00:43:31.160 | bone mass, gonad function, et cetera,

00:43:34.340 | you can understand why it would make sense

00:43:36.680 | to be cautious about melatonin supplementation,

00:43:38.980 | because supplementation tends to be pretty static.

00:43:41.480 | It's X number of milligrams per night.

00:43:44.460 | Whereas normally, endogenously,

00:43:47.220 | the amount of melatonin that you're releasing each night

00:43:49.420 | is changing according to time of year.

00:43:52.140 | Or if you happen to live in an area

00:43:54.340 | where there isn't much change in day length across the year.

00:43:56.940 | So for instance, if you live near the equator,

00:43:59.140 | well, then your body is accustomed

00:44:00.920 | to having regular amounts of melatonin each night.

00:44:04.020 | When you start supplementing melatonin,

00:44:06.180 | you start changing the total amount of melatonin, obviously,

00:44:09.240 | but you're also changing the normal rhythms

00:44:12.240 | in how much melatonin is being released

00:44:14.980 | into your brain and body across the 365 day calendar year.

00:44:19.000 | So while I'm somebody who readily embraces supplementation

00:44:22.940 | in various forms for things like sleep and focus, et cetera,

00:44:26.360 | when it comes to melatonin, I'm extremely cautious.

00:44:30.080 | And I think it's also one of the few examples

00:44:32.580 | where a hormone is available without prescription

00:44:35.820 | over the counter.

00:44:36.660 | You can just go into a pharmacy or drug store,

00:44:38.020 | order online this hormone,

00:44:39.620 | which is known to have all these powerful effects.

00:44:41.880 | So I get very, very concerned

00:44:43.620 | when I hear about people taking melatonin,

00:44:45.740 | especially at the levels that are present

00:44:47.380 | in most supplements.

00:44:48.560 | It's been recognized for a very long time.

00:44:50.580 | And in fact, there are now data to support the fact

00:44:53.540 | that animals of all kinds, including humans,

00:44:56.580 | will seek out mates and engage in mating behavior

00:44:59.860 | more frequently during the long days of spring and summer.

00:45:04.140 | That's right, in seasonally breeding animals,

00:45:06.820 | of course, this is the case, but in humans as well,

00:45:10.860 | there is more seeking out of mates and mating behavior

00:45:13.780 | in longer day times of year.

00:45:16.840 | Now you could imagine at least two mechanisms

00:45:19.540 | by which this occurs.

00:45:21.520 | The first mechanism we could easily map to melatonin

00:45:25.360 | and the fact that melatonin is suppressive

00:45:28.000 | to various aspects of the so-called gonadal axis,

00:45:31.440 | which is basically a fancy way of saying

00:45:34.020 | that melatonin inhibits testosterone and estrogen output

00:45:37.700 | from the testes and from the ovaries.

00:45:40.100 | I just want to remind people that both males and females

00:45:42.280 | make testosterone and estrogen,

00:45:44.680 | although in different ratios,

00:45:45.820 | typically in males versus females,

00:45:47.580 | and that both testosterone and estrogen are critical

00:45:51.720 | for the desire to mate and for mating behavior.

00:45:55.860 | There's a broad misconception that testosterone

00:45:58.860 | is involved in mating behavior

00:46:00.280 | and estrogen is involved in other behaviors,

00:46:01.980 | but having enough estrogen is critical

00:46:04.640 | for both males and females

00:46:05.920 | in order to maintain the desire to mate

00:46:08.060 | and indeed the ability to mate.

00:46:10.160 | I discussed this on the episode

00:46:11.960 | on optimizing testosterone and estrogen.

00:46:14.320 | So if you'd like more details on that,

00:46:15.940 | please see that episode of the Huberman Lab Podcast.

00:46:19.300 | Okay, so if melatonin is suppressive

00:46:22.840 | to the so-called gonadal axis

00:46:25.380 | and reduces overall levels of testosterone and estrogen

00:46:28.660 | in males and females, and light inhibits melatonin,

00:46:33.520 | then when there's more light, then there's less melatonin

00:46:36.700 | and more hormone output from the gonads.

00:46:39.540 | And indeed that's how the system works,

00:46:41.700 | but that's not the entire story.

00:46:43.700 | It turns out that there is a second

00:46:46.100 | so-called parallel pathway,

00:46:47.780 | meaning a different biological pathway

00:46:50.500 | that operates in parallel

00:46:52.300 | to the light suppression of melatonin pathway

00:46:55.460 | that provides a basis for longer days inspiring more desire

00:46:59.980 | to mate and more mating behavior.

00:47:02.040 | So if we think of the first pathway involving melatonin

00:47:05.220 | as sort of a break on these reproductive hormones,

00:47:08.480 | the second mechanism is more like an accelerator

00:47:11.100 | on those hormones, and yet it still involves light.

00:47:15.060 | As I'm about to tell you, in animals such as mice,

00:47:18.740 | but also in humans, exposure to light,

00:47:22.320 | in particular UV blue light, so short wavelengths of light,

00:47:26.120 | can trigger increases in testosterone and estrogen

00:47:29.180 | and the desire to mate.

00:47:30.800 | Now what's especially important about this accelerator

00:47:33.640 | on the desire to mate and mating behavior and hormones

00:47:36.820 | is that it is driven by exposure to light,

00:47:40.920 | but it is not the exposure of light to the eyes.

00:47:44.740 | It turns out that it is the exposure of your skin

00:47:48.120 | to particular wavelengths of light

00:47:50.200 | that is triggering increases in the hormones,

00:47:52.840 | testosterone and estrogen,

00:47:54.460 | leading to increased desire to mate.

00:47:57.020 | As it turns out, your skin,

00:47:59.220 | which most of us just think of as a way

00:48:01.400 | to protect the organs of our body

00:48:03.340 | or something to hang clothes on or ornaments on

00:48:06.300 | if you're somebody who has earrings and so forth,

00:48:09.440 | your skin is actually an endocrine organ,

00:48:12.340 | meaning it is a hormone producing

00:48:15.180 | and hormone influencing organ.

00:48:17.360 | I promise what I'm about to tell you next

00:48:19.680 | will forever change the way that you think about your skin

00:48:22.600 | and light and the desire to mate

00:48:25.760 | and indeed even mating behavior.

00:48:28.400 | I think the results are best understood

00:48:30.580 | by simply going through the primary data,

00:48:33.000 | meaning the actual research on this topic.

00:48:35.360 | And to do so, I'm going to review a recent paper

00:48:37.560 | that was published in the journal Cell Reports,

00:48:39.960 | Cell Press Journal, excellent journal.

00:48:42.080 | This is a paper that came out in 2021

00:48:44.360 | entitled Skin Exposure to UVB Light

00:48:48.640 | Induces a Skin Brain GONAD Axis and Sexual Behavior.

00:48:53.080 | And I want to emphasize that this was a paper

00:48:55.760 | that focused on mice in order to address specific mechanisms

00:49:00.560 | because in mice, you can so-called knock out

00:49:03.400 | particular genes, you can remove particular genes

00:49:05.540 | to understand mechanism.

00:49:06.600 | You just can't do that in humans

00:49:08.160 | in any kind of controlled way,

00:49:09.980 | at least not at this point in time.

00:49:12.440 | And this study also explores humans

00:49:15.360 | and looked at human subjects, both men and women.

00:49:18.840 | The basic finding of this study was that when mice

00:49:23.240 | or humans were exposed to UVB,

00:49:26.280 | meaning ultraviolet blue light,

00:49:27.600 | so short wavelength light of the sort

00:49:29.120 | that comes through in sunshine,

00:49:30.960 | but is also available through various artificial sources.

00:49:34.300 | If they received enough exposure of that light

00:49:39.180 | to their skin, there were increases in testosterone

00:49:44.100 | that were observed within a very brief period of time,

00:49:47.000 | also increases in the hormone estrogen.

00:49:50.080 | And I should point out that the proper ratios of estrogen

00:49:52.760 | and testosterone were maintained in both males and females,

00:49:55.800 | at least as far as these data indicate.

00:49:58.740 | And mice tended to seek out mating more and mate more.

00:50:03.740 | There were also increases in gonadal weight,

00:50:07.580 | literally increases in testes size and in ovarian size

00:50:11.260 | when mice were exposed to this UVB light

00:50:14.040 | past a certain threshold.

00:50:15.500 | Now, as I mentioned before, the study also looked at humans.

00:50:18.160 | They did not look at testes size or ovarian size

00:50:21.940 | in the human subjects.

00:50:23.240 | However, because they are humans,

00:50:25.240 | they did address the psychology of these human beings

00:50:28.960 | and address whether or not they had increases in,

00:50:31.680 | for instance, aggressiveness or in passionate feelings

00:50:34.800 | and how their perception of other people changed

00:50:38.660 | when they were getting a lot of UVB light exposure

00:50:42.320 | to the skin.

00:50:43.200 | So before I get into some of the more important details

00:50:45.360 | of the study and how it was done

00:50:47.040 | and how you can leverage this information for yourself,

00:50:49.760 | if you desire, I just want to highlight

00:50:52.800 | some of the basic findings overall.

00:50:55.600 | UVB exposure increased these so-called sex steroid levels

00:50:59.380 | in mice and humans.

00:51:00.680 | The sex steroid hormones, when we say steroids,

00:51:03.780 | we don't mean anabolic steroids taken exogenously.

00:51:06.480 | I think when people hear the word steroids,

00:51:07.880 | they always think steroid abuse or use.

00:51:10.640 | Rather steroid hormones such as testosterone and estrogen

00:51:13.900 | went up when mice or humans had a lot of UVB exposure

00:51:18.300 | to their skin.

00:51:19.200 | Second of all, UVB light exposure to the skin

00:51:22.780 | enhanced female attractiveness.

00:51:24.640 | So the perceived attractiveness of females by males

00:51:27.780 | and increase the receptiveness or the desire to mate

00:51:31.880 | in both sexes.

00:51:33.340 | UVB light exposure also changed various aspects

00:51:36.640 | of female biology related to fertility,

00:51:39.020 | in particular, follicle growth.

00:51:41.480 | Follicle and egg maturation are well-known indices

00:51:45.820 | of fertility and of course correlate with the menstrual

00:51:49.160 | cycle in adult humans and is related overall

00:51:52.860 | to the propensity to become pregnant.

00:51:56.200 | UVB light exposure enhanced maturation of the follicle,

00:51:59.340 | which just meant that more healthy eggs were being produced.

00:52:02.540 | These are impressive effects.

00:52:03.880 | First of all, they looked at a large number of variables

00:52:06.400 | in the study and the fact that they looked at mice

00:52:08.500 | and humans is terrific.

00:52:10.140 | I think that oftentimes we find it hard to translate data

00:52:13.060 | from mice to humans.

00:52:13.900 | So the fact that they looked at both in parallel

00:52:16.260 | is wonderful.

00:52:17.160 | In the mice and in the humans,

00:52:20.260 | they established a protocol that essentially involved

00:52:24.500 | exposing the skin to UV light that was equivalent

00:52:27.820 | to about 20 to 30 minutes of midday sun exposure.

00:52:31.340 | Now, of course, where you live in the world

00:52:33.060 | will dictate whether or not that midday sun

00:52:34.700 | is very, very bright and intense or is less bright.

00:52:37.640 | Maybe there's cloud cover, et cetera.

00:52:39.360 | But since I'm imagining that most people are interested

00:52:43.080 | in the ways to increase testosterone and or estrogen

00:52:46.560 | in humans and are not so much interested

00:52:48.840 | in increasing testosterone in mice,

00:52:51.060 | I'm going to just review what they did

00:52:52.800 | in the human population or the human subjects.

00:52:55.900 | What they did is they had people first of all,

00:52:58.920 | establish a baseline and the way they establish a baseline

00:53:01.320 | was a little bit unusual,

00:53:02.640 | but it will make perfect sense to you.

00:53:04.520 | They had people wear long sleeves and essentially cover up

00:53:06.940 | and avoid sunlight for a few days

00:53:08.780 | so they could measure their baseline hormones

00:53:10.720 | in the absence of getting a lot of UVB light exposure

00:53:14.680 | from the sun or from other sources.

00:53:16.600 | Now, of course, these people had access

00:53:18.840 | to artificial lights,

00:53:19.980 | but as I've pointed out on this podcast before,

00:53:22.040 | it's pretty unusual that you'll get enough UVB exposure

00:53:25.420 | from artificial lights throughout the day

00:53:28.000 | and in the morning, you need a lot of UVB exposure

00:53:30.660 | or we should be getting a lot of UVB exposure

00:53:33.440 | to our eyes and to our face and to our skin

00:53:35.400 | throughout the day, provided we're not getting sunburn.

00:53:37.700 | This is actually a healthy thing for mood

00:53:39.600 | and for energy throughout the day.

00:53:41.180 | It's only at night, basically between the hours

00:53:43.880 | of about 10 PM and 4 AM that even a tiny bit of UVB exposure

00:53:48.740 | from artificial sources can mess us up

00:53:50.760 | in terms of our sleep and our energy levels and so on

00:53:53.420 | and that's because of the potent effect of UVB

00:53:55.840 | on suppressing melatonin.

00:53:58.040 | So the point here is that they establish a baseline

00:54:01.200 | whereby people were getting some artificial light exposure

00:54:04.200 | throughout the day, but they weren't getting outside a lot.

00:54:06.660 | They weren't getting a lot of sunlight.

00:54:08.360 | And then they had people receive a dose

00:54:11.700 | of UVB light exposure.

00:54:14.020 | That was about 20 to 30 minutes outdoors.

00:54:16.820 | They had people wear short sleeves, no hat, no sunglasses.

00:54:20.320 | Some people wore sleeveless shirts.

00:54:21.880 | They encouraged people to wear shorts.

00:54:23.560 | So they were indeed wearing clothing.

00:54:25.960 | They were not naked and they were wearing clothing

00:54:28.920 | that was culturally and situationally appropriate

00:54:31.440 | at least for the part of the world where this study was done

00:54:34.360 | and they had people do that two or three times a week.

00:54:37.120 | So in terms of a protocol that you might export

00:54:39.120 | from this study, basically getting outside

00:54:40.980 | for about 30 minutes, two or three times a week

00:54:43.320 | in a minimum of clothing and yet still wearing

00:54:46.520 | enough clothing that is culturally appropriate.

00:54:48.920 | They were outside, they weren't sunbathing,

00:54:51.160 | flipping over on their back and front.

00:54:52.560 | They were just moving about doing things they could read.

00:54:54.720 | They could talk, they could go about other activities

00:54:57.520 | but they weren't wearing a broad brim hat

00:54:59.540 | or a hat of any kind, just getting a lot of sun exposure

00:55:01.800 | to their skin.

00:55:02.640 | They did this for a total of 10 to 12 UVB treatments.

00:55:07.960 | So this took several weeks, right?

00:55:10.040 | It took about a month if you think about it,

00:55:11.400 | two or three times per week for a total

00:55:12.760 | of 10 to 12 UVB treatments.

00:55:15.760 | These treatments of course are just being outside

00:55:17.280 | in the sun and then they measured hormones

00:55:20.880 | and they measured the psychology of these male

00:55:23.180 | and female adult subjects.

00:55:24.920 | Let's first look at the psychological changes

00:55:27.080 | that these human subjects experienced

00:55:28.960 | after getting 10 to 12 of these UVB light exposure,

00:55:33.060 | outdoor and sunlight type treatments.

00:55:35.360 | They did this by collecting blood samples

00:55:37.080 | throughout the study and they saw significant increases

00:55:40.940 | in the hormones beta estradiol,

00:55:42.720 | which is one of the major forms of estrogen,

00:55:45.240 | progesterone, another important steroid hormone

00:55:48.400 | and testosterone in both men and women.

00:55:51.680 | Now an important point is that the testosterone increases

00:55:55.200 | were significantly higher in men that happened

00:55:58.640 | to originate from countries that had low UV exposure

00:56:03.000 | compared to individuals from countries

00:56:05.520 | with high UV exposure.

00:56:07.960 | Now this ought to make sense if we understand a little bit

00:56:11.340 | about how the skin functions as an endocrine organ.

00:56:13.980 | Many of you have probably heard of vitamin D3,

00:56:17.040 | which is a vitamin that we all make.

00:56:19.680 | Many people supplement it as well

00:56:21.180 | if they need additional vitamin D3.

00:56:24.280 | We all require sunlight in order to allow vitamin D3

00:56:28.800 | to be synthesized and perform its roles in the body.

00:56:32.160 | And it turns out that people who have darker skin

00:56:35.120 | actually need more vitamin D3 and or more sunlight exposure

00:56:39.680 | in order to activate that D3 pathway

00:56:42.180 | than do people with paler skin.

00:56:45.240 | And this should make sense to all of you

00:56:47.440 | given what you now understand about melanocytes,

00:56:50.160 | that cell type that we discussed earlier

00:56:51.720 | because melanocytes have pigment within them.

00:56:54.800 | And if you have darker skin,

00:56:56.640 | it means that you have more melanocytes

00:56:59.260 | or that you have melanocytes that are more efficient

00:57:02.120 | at creating pigment.

00:57:03.960 | And as a consequence, the light that lands on your skin

00:57:07.680 | will be absorbed by those melanocytes

00:57:09.380 | and less of it is able to impact the D3 pathway.

00:57:12.720 | Whereas if you have pale skin,

00:57:14.040 | more of the light that lands on your skin

00:57:16.080 | can trigger the synthesis and assist the actions

00:57:20.880 | of vitamin D3.

00:57:22.340 | Similarly, in this study,

00:57:23.560 | they found that people who had paler skin

00:57:25.760 | and or who originated from countries

00:57:28.180 | where they had less UVB light exposure across the year

00:57:32.260 | had greater meaning more significant increases

00:57:35.480 | in testosterone overall than did people

00:57:37.880 | who already were getting a lot of UVB exposure.

00:57:41.080 | This led them to explore so-called seasonal changes

00:57:43.800 | in testosterone that occurred normally in the absence

00:57:47.680 | of any light exposure treatment.

00:57:49.660 | So up until now, I've been talking about the aspects

00:57:52.640 | of this study involving people getting outside

00:57:55.140 | for about 20 to 30 minutes per day in sunlight

00:57:57.960 | in a minimum of clothing.

00:57:59.440 | There was an increase in testosterone observed

00:58:01.840 | in both men and women.

00:58:03.240 | The increases in testosterone were greater for people

00:58:05.800 | that had paler skin than darker skin.

00:58:08.520 | So the data I'm about to describe

00:58:10.220 | also come from this same paper,

00:58:11.920 | but do not involve 20 to 30 minute

00:58:14.360 | daily sun exposure protocols.

00:58:16.080 | It's simply addressing whether or not testosterone levels

00:58:19.660 | change as a function of time of year.

00:58:22.540 | They measured testosterone across the 12 month calendar.

00:58:27.820 | This study was done on subjects living

00:58:29.660 | in the Northern hemisphere for the entire year.

00:58:32.180 | And so in the months of January, February, and March,

00:58:35.500 | of course, the length of days is shortest

00:58:38.620 | and the length of nights is longest.

00:58:41.060 | And of course, in the spring and summer months,

00:58:43.620 | June, July, August, September, and so on,

00:58:45.700 | the days are much longer and the nights are shorter.

00:58:47.760 | And what they observed was very obvious.

00:58:50.600 | They observed that testosterone levels were lowest

00:58:55.380 | in the winter months and were highest in the months

00:58:58.380 | of June, July, August, and September.

00:59:01.260 | Now, these are very important data.

00:59:03.040 | At least to my knowledge,

00:59:03.880 | these are the first data systematically exploring

00:59:06.840 | the levels of sex steroid hormones in humans

00:59:09.960 | as a function of time of year and thereby as a function

00:59:13.420 | of how much sunlight exposure they're getting.

00:59:15.980 | And what's remarkable about these data is

00:59:18.060 | that they map very well to the data in mice

00:59:20.660 | and the other data in this paper on humans,

00:59:23.560 | which illustrate that if you're getting more UVB exposure,

00:59:28.000 | your testosterone levels are higher.

00:59:29.780 | This study went a step further and explored whether

00:59:31.940 | or not the amount of sunlight exposure

00:59:33.740 | that one is getting to their skin influences

00:59:36.060 | their psychology in terms of whether

00:59:38.740 | or not they have increased desire to mate and so on.

00:59:41.560 | It's well known that sunlight exposure

00:59:43.940 | to the eyes can increase mood.

00:59:46.760 | And I talked about this in the podcast episode

00:59:49.040 | with my guest, Dr. Samir Hatar,

00:59:50.980 | who's the director of the Chronobiology Unit

00:59:52.760 | at the National Institutes of Mental Health.

00:59:54.380 | And Samir's recommendation is that people get

00:59:56.260 | as much bright light exposure as they safely can

00:59:58.800 | in the morning and throughout the day for sake

01:00:00.620 | of both sleep and energy, but also for enhancing mood

01:00:04.980 | and regulating appetite.

01:00:06.860 | In this study, it was found that both males

01:00:10.100 | and females had higher levels of romantic passion

01:00:13.340 | after getting the UV treatment.

01:00:16.140 | In fact, some of them reported increases

01:00:17.860 | in romantic passion from just one

01:00:19.560 | or two of these UV treatments.

01:00:21.480 | So they didn't have to go through all 10 or 12

01:00:24.160 | in order to get a statistically significant increase

01:00:26.960 | in passion.

01:00:28.400 | Now, when we talk about passion,

01:00:30.020 | as the authors of this paper acknowledge,

01:00:31.980 | there's really two forms.

01:00:32.940 | There is emotional and sexual,

01:00:34.640 | and they parse this pretty finely.

01:00:36.380 | I don't want to go into all the details

01:00:37.920 | and we can provide a reference and link to this study

01:00:39.740 | if you'd like to look at those details.

01:00:41.740 | But what they found was that women receiving

01:00:45.100 | this UVB light exposure focused more on increases

01:00:49.500 | in physical arousal and sexual passion,

01:00:51.740 | whereas the men actually scored higher

01:00:53.700 | on the cognitive dimensions of passion,

01:00:55.580 | such as obsessive thoughts about their partner and so on.

01:00:58.220 | Regardless, both males and females experienced

01:01:02.220 | and reported a increase in sexual passion

01:01:05.420 | and desire to mate.

01:01:06.880 | And we now know there were increases in testosterone

01:01:09.580 | and estrogen, which of course could be driving

01:01:11.940 | the psychological changes.

01:01:13.180 | Although I'm sure that those interact in both directions,

01:01:15.820 | meaning the hormones no doubt affect psychology

01:01:19.380 | and no doubt the psychology,

01:01:21.180 | these changes in passionate feelings,

01:01:22.940 | no doubt also increased or changed

01:01:25.420 | the hormone levels as well.

01:01:26.920 | And I want to reemphasize that there was a component

01:01:30.620 | of the study that had no deliberate daylight,

01:01:33.620 | sunlight exposure for 20 or 30 minutes,

01:01:36.340 | but rather just looked at hormone levels

01:01:38.500 | throughout the year and found that the increase

01:01:42.400 | in day length correlated with increases

01:01:45.420 | in testosterone and sexual passion.

01:01:47.420 | Now, my opinion, this is a very noteworthy study

01:01:50.140 | because it really illustrates that sunlight

01:01:53.740 | and day length can impact the melatonin pathway

01:01:56.420 | and thereby take the foot off the brake, so to speak,

01:02:00.580 | on testosterone, estrogen, and the desire to mate.

01:02:03.980 | It also emphasizes that sunlight, UVB light,

01:02:08.220 | can directly trigger hormone pathways

01:02:11.360 | and desire to mate and mating behavior.

01:02:14.080 | Now, this study went a step further

01:02:15.460 | in defining the precise mechanism

01:02:17.500 | by which light can impact all these hormones

01:02:19.740 | and this desire to mate.

01:02:21.540 | And here, understanding the mechanism is key

01:02:23.660 | if you want to export a particular protocol

01:02:26.140 | or tool that you might apply.

01:02:27.800 | We talked earlier about how UVB light exposure

01:02:31.700 | to the eyes triggers activation

01:02:33.380 | of these particular neurons within the eye

01:02:35.620 | and then with centers deeper in the brain

01:02:37.940 | and eventually the pineal gland

01:02:39.780 | to suppress the output of melatonin

01:02:42.140 | and thereby to allow testosterone and estrogen

01:02:45.020 | to exist at higher levels

01:02:46.180 | because melatonin can inhibit testosterone and estrogen.

01:02:50.580 | In this study, they were able to very clearly establish

01:02:54.100 | that it is sunlight exposure to our skin

01:02:57.460 | that is causing these hormone increases

01:02:59.420 | that they observed in mice and humans.

01:03:02.120 | And the way they did that was to use

01:03:05.020 | the so-called knockout technology,

01:03:06.640 | the ability to remove specific genes

01:03:08.700 | within specific tissues of the body.

01:03:11.100 | And what they found is that UVB light,

01:03:13.600 | meaning sunlight exposed skin upregulated,

01:03:18.000 | meaning increased the activity of something called P53,

01:03:20.980 | which is involved in the maturation of cells

01:03:24.020 | and various aspects of cellular function.

01:03:25.980 | And the cells they were focused on were the keratinocytes,

01:03:29.840 | which you are now familiar with from our earlier discussion

01:03:32.520 | about the fact that the epidermis of your skin

01:03:35.100 | contains mainly keratinocytes and melanocytes.

01:03:37.980 | Sunlight exposure increased P53 activity in the skin

01:03:43.020 | and P53 activity was required

01:03:46.220 | for the downstream increases in ovarian size,

01:03:49.420 | in testicular size, in testosterone increases,

01:03:53.680 | in the estrogen increases

01:03:55.540 | and the various other changes that they observed

01:03:58.460 | at the physiological level

01:03:59.980 | when animals or humans were exposed to sunlight.

01:04:03.060 | So these data are important

01:04:04.060 | because what they mean is that not only is it important

01:04:06.900 | that we get sunlight exposure early in the day

01:04:09.820 | and throughout the day to our eyes,

01:04:11.660 | at least as much as is safely possible,

01:04:14.000 | but that we also need to get UVB sunlight exposure

01:04:16.700 | onto our skin if we want to activate this P53 pathway

01:04:21.020 | in keratinocytes and the testosterone and estrogen increases

01:04:25.660 | that are downstream of that P53 pathway.

01:04:28.380 | So even though the gene knockout studies were done on mice,

01:04:33.220 | they clearly show that if you remove P53 from the skin,

01:04:36.580 | that these effects simply do not occur.

01:04:39.220 | So in terms of thinking about a protocol

01:04:41.600 | to increase testosterone and estrogen,

01:04:43.540 | mood and feelings of passion,

01:04:45.860 | the idea is that you would want to get

01:04:48.420 | this two to three exposures per week minimum

01:04:52.620 | of 20 to 30 minutes of sunlight exposure

01:04:55.460 | onto as much of your body

01:04:57.440 | as you can reasonably expose it to.

01:05:00.380 | And when I say reasonably, I mean,

01:05:02.020 | of course you have to obey cultural constraints,

01:05:04.360 | decency constraints, and of course you have to also obey

01:05:08.180 | the fact that sunlight can burn your skin.

01:05:10.620 | So many people are probably going to ask,

01:05:13.020 | what happens if you wear sunscreen?

01:05:15.980 | In theory, because sunscreen has UV protection,

01:05:19.700 | it would block some of these effects.

01:05:21.840 | Now I'm not suggesting that people do away

01:05:23.380 | with sunscreen entirely.

01:05:24.540 | I do hope to do an episode all about sunscreen

01:05:27.140 | in the future because sunscreen

01:05:29.000 | is a bit of a controversial topic.

01:05:30.960 | Skin cancers are a real thing

01:05:32.720 | and many people are especially prone to skin cancer.

01:05:35.620 | So you need to take that seriously.

01:05:37.540 | Some people are not very prone to skin cancers

01:05:39.800 | and can tolerate much more sun exposure.

01:05:42.620 | You're probably familiar with the simple fact

01:05:44.480 | that if you've gone outside on the beach with friends,

01:05:47.900 | some people get burned very easily, others don't.

01:05:49.960 | So you really should prioritize the health

01:05:52.440 | and the avoidance of sunburn on your skin.

01:05:54.840 | However, these data and other data point to the fact

01:05:58.740 | that we should all probably be striving

01:06:01.500 | to get more sunlight exposure

01:06:03.460 | onto our skin during the winter months

01:06:05.680 | and still getting sunlight exposure

01:06:07.620 | onto our skin in the summer months,

01:06:10.020 | provided we can do that without damaging our skin.

01:06:12.740 | Another set of very impressive effects of UVB light,

01:06:15.640 | whether or not it comes from sunlight

01:06:16.740 | or from an artificial source,

01:06:18.920 | is the effect of UVB light on our tolerance for pain.

01:06:22.400 | It turns out that our tolerance for pain

01:06:24.320 | varies across the year

01:06:26.160 | and that our pain tolerance is increased

01:06:29.360 | in longer day conditions.

01:06:32.120 | And as we saw with the effects of UVB

01:06:34.840 | on hormones and mating,

01:06:36.640 | again, this is occurring via UVB exposure to the skin

01:06:42.100 | and UVB exposure to the eyes.

01:06:45.120 | I want to just describe two studies

01:06:46.720 | that really capture the essence of these results.

01:06:49.480 | I'm going to discuss these in kind of a top contour fashion.

01:06:52.500 | I won't go into it as quite as much depth

01:06:54.220 | as I did the last study,

01:06:55.400 | but I will provide links to these studies as well.

01:06:57.960 | The first study is entitled

01:07:00.880 | skin exposure to ultraviolet B rapidly activates

01:07:04.560 | systemic neuroendocrine and immunosuppressive responses.

01:07:07.520 | And you might hear that and think,

01:07:08.400 | oh, immunosuppressive, that's bad.

01:07:09.860 | But basically what they observed

01:07:11.520 | is that even one exposure to UVB light

01:07:16.200 | changed the output of particular hormones

01:07:18.440 | and neurochemicals in the body,

01:07:20.060 | such as corticotropin hormone and beta endorphins,

01:07:23.640 | which are these endogenous opioids.

01:07:25.720 | We've all heard of the opioid crisis,

01:07:27.280 | which is people getting addicted to opioids

01:07:29.440 | that they are taking in drug form, pharmaceuticals.

01:07:32.800 | But here I'm referring to endorphins

01:07:35.040 | that our body naturally manufactures and releases

01:07:37.520 | in order to counter pain

01:07:39.240 | and act as a somewhat of a psychological soother also,

01:07:44.080 | because of course, physical pain and emotional pain

01:07:46.360 | are intimately linked in the brain and body.

01:07:48.720 | What they found was that exposure to UVB light

01:07:51.940 | increased the release of these beta endorphins.

01:07:55.040 | It caused essentially the release

01:07:56.600 | of an endogenous painkiller.

01:07:59.380 | Now, a second study that came out very recently,

01:08:03.000 | just this last week in fact,

01:08:04.780 | published in the journal neuron,

01:08:06.020 | cell press journal, excellent journal,

01:08:08.260 | is entitled a visual circuit

01:08:09.880 | related to the periaqueductal gray area

01:08:12.380 | for the anti-nociceptive effects of bright light treatment.

01:08:15.300 | I'll translate a little bit of that for you.

01:08:17.980 | The periaqueductal gray is a region of the midbrain

01:08:21.620 | that contains a lot of neurons

01:08:24.160 | that can release endogenous opioids.

01:08:26.840 | Things like beta enkephalin, things like enkephalin,

01:08:30.800 | things like mu opioid.

01:08:32.200 | These are all names of chemicals

01:08:34.320 | that your body can manufacture

01:08:35.640 | that act as endogenous painkillers

01:08:37.600 | and increase your tolerance for pain.

01:08:39.480 | They actually make you feel less pain overall

01:08:41.880 | by shutting down some of the neurons that perceive pain

01:08:45.360 | or by reducing their activity, not to a dangerous level.

01:08:48.640 | They're not going to block the pain response

01:08:50.140 | so that you burn yourself unnecessarily

01:08:52.620 | or harm yourself unnecessarily,

01:08:54.140 | but they act as a bit of a painkiller from the inside.

01:08:57.520 | If you heard the word anti-nociceptive,

01:09:01.240 | nociception is basically the perception

01:09:05.160 | or the way in which neurons respond to painful stimuli.

01:09:09.400 | So you can think of nociceptive events

01:09:11.680 | in your nervous system as painful events.

01:09:14.040 | And there I'm using a broad brush.

01:09:15.720 | I realized that the experts in pain will say,

01:09:17.520 | "Oh, it's not a really a pain circuit, et cetera, et cetera."

01:09:20.460 | But for sake of today's discussion,

01:09:22.840 | it's fair to say that nociception is the perception of pain.

01:09:26.480 | So if this title is a visual circuit

01:09:29.120 | related to the periaqueductal gray,

01:09:31.320 | which is this area that releases these endogenous opioids

01:09:34.200 | for the anti-nociceptive,

01:09:35.560 | the anti-pain effects of bright light treatment.

01:09:38.360 | The key finding of this study

01:09:41.520 | is that it is light landing on the eyes

01:09:45.220 | and captured by the specific cells

01:09:48.080 | I was talking about earlier,

01:09:48.980 | those intrinsically photosensitive melanopsin ganglion cells

01:09:52.220 | is the long name for them.

01:09:53.060 | But these particular neurons in your eye

01:09:54.940 | and in my eye, incidentally,

01:09:57.300 | that communicate with particular brain areas.

01:10:00.580 | These brain areas have names if you want to know them

01:10:03.180 | for you aficionados or for you ultra curious folks,

01:10:05.740 | they have names like the ventrolateral geniculate nucleus

01:10:08.100 | and the intergeniculate leaflet.

01:10:09.580 | The names don't matter.

01:10:10.780 | The point is that light landing on the eyes

01:10:13.400 | is captured by these melanopsin cells.

01:10:16.680 | They absorb that light,

01:10:18.000 | translate that light into electrical signals

01:10:20.220 | that are handed off to areas of the brain,

01:10:22.000 | such as the ventral geniculate.

01:10:24.440 | And then the ventral geniculate

01:10:26.880 | communicates with this periaqueductal gray area

01:10:30.280 | to evoke the release of these endogenous opioids

01:10:33.960 | that soothe you and lead to less perception of pain.

01:10:38.000 | This is a really important study

01:10:39.360 | because it's long been known that in longer days

01:10:43.360 | or in bright light environments,

01:10:44.620 | we tolerate emotional and physical pain better.

01:10:47.380 | Previous studies had shown that it is light landing

01:10:51.300 | on our skin that mediates that effect, but only in part,

01:10:55.460 | it couldn't explain the entire effect.

01:10:57.400 | This very recent study indicates

01:10:59.380 | that it's also light arriving at the eyes.

01:11:02.380 | And in this case, again, UVB light,

01:11:04.700 | ultraviolet blue light of the sort that comes from sunlight,

01:11:08.380 | that is triggering these anti-pain or pain relieving pathways.

01:11:12.700 | So once again, we have two parallel pathways.

01:11:15.200 | This is a theme you're going to hear

01:11:16.320 | over and over and over again, not just in this episode,

01:11:19.380 | but in all episodes of the Huberman Lab Podcast,

01:11:21.460 | because this is the way that your brain and body are built.

01:11:24.760 | Nature rarely relies on one mechanism

01:11:27.920 | in order to create an important phenomenon.

01:11:30.200 | And pain relief is an important phenomenon.

01:11:32.400 | So we now have at least two examples

01:11:34.400 | of the potent effects of UVB light exposure

01:11:37.960 | to the skin and to the eyes.

01:11:39.580 | One involving activation of testosterone

01:11:44.280 | and estrogen pathways as it relates to mating,

01:11:46.340 | and another that relates to reducing the total amount

01:11:50.200 | of pain that we experience in response

01:11:52.240 | to any painful stimuli.

01:11:54.200 | So for those of you that are thinking tools and protocols,

01:11:57.160 | if you're somebody who's experiencing chronic pain,

01:12:00.120 | provided you can do it safely,

01:12:01.760 | try to get some UVB exposure, ideally from sunlight.

01:12:06.180 | I think the 20 to 30 minute protocol,

01:12:07.920 | two or three times per week is an excellent one.

01:12:10.520 | It seems like a fairly low dose of UVB light exposure.

01:12:14.280 | It's hard to imagine getting much damage to the skin.

01:12:17.340 | Of course, if you have very sensitive skin,

01:12:19.740 | or if you live in an area of the world that is very,

01:12:22.660 | very bright and has intense sunlight,

01:12:25.400 | particular times of year, you'll want to be cautious.

01:12:27.820 | Heed the warnings and considerations about sunscreen

01:12:30.460 | that I talked about earlier or about wearing a hat.

01:12:32.880 | But the point is very clear.

01:12:34.860 | Most of us should be getting more UVB exposure

01:12:38.260 | from sunlight.

01:12:39.120 | I can already hear the screams within the comments

01:12:42.540 | or the rather the questions within the comments saying,

01:12:44.620 | well, what if I live in a part of the world

01:12:46.220 | where I don't get much UVB exposure?

01:12:48.760 | And I want to emphasize something that I've also emphasized

01:12:51.340 | in the many discussions on this podcast related

01:12:53.540 | to sleep and circadian rhythms and alertness,

01:12:55.460 | which is even on a cloud covered day,

01:12:59.380 | you are going to get far more light energy photons

01:13:03.160 | through cloud cover than you are going to get

01:13:06.640 | from an indoor light source, an artificial light source.

01:13:10.140 | I can't emphasize this enough.

01:13:12.700 | If you look outside in the morning and you see some sunlight,

01:13:16.100 | if you see some sunlight throughout the day,

01:13:17.740 | you would do yourself a great favor to try

01:13:20.700 | and chase some of that sunlight and get into that sunlight,

01:13:24.120 | to expose your eyes and your skin to that sunlight,

01:13:27.020 | as much as you safely can.

01:13:28.140 | And when I say as much as you safely can,

01:13:30.560 | never ever look at any light,

01:13:31.900 | artificial sunlight or otherwise that's so bright

01:13:34.220 | that it's painful to look at.

01:13:35.300 | It's fine to get that light arriving

01:13:37.080 | on your eyes indirectly.

01:13:38.820 | It's fine to wear eyeglasses or contact lenses.

01:13:41.340 | In fact, if you think about the biology of the eye

01:13:43.540 | and the way that those lenses work,

01:13:45.080 | that it will just serve to focus that light

01:13:47.480 | on to the very cells that you want those light beams

01:13:50.740 | to be delivered to.

01:13:51.900 | Whereas sunglasses that are highly reflective

01:13:54.160 | or trying to get your sunlight exposure

01:13:56.000 | through a windshield of a car or through a window

01:13:59.080 | simply won't work.

01:14:00.940 | I'm sorry to tell you,

01:14:02.060 | but most windows are designed to filter out the UVB light.

01:14:06.220 | And if you're somebody who's really keen on blue blockers

01:14:09.020 | and you're wearing your blue blockers all day,

01:14:11.000 | well, don't wear them outside.

01:14:13.020 | And in fact, you're probably doing yourself a disservice

01:14:15.900 | by wearing them in the morning and in the daytime.

01:14:18.260 | There certainly is a place for blue blockers

01:14:20.100 | in the evening and nighttime,

01:14:21.320 | if you're having issues with falling and staying asleep.

01:14:24.140 | But if you think about it, blue blockers,

01:14:26.020 | what they're really doing

01:14:26.860 | is blocking those short wavelength UVB wavelengths of light

01:14:30.880 | that you so desperately need to arrive at your retina.

01:14:33.820 | And of course, also onto your skin

01:14:35.940 | in order to get these powerful biological effects

01:14:38.620 | on hormones and on pain reduction.

01:14:40.680 | And in terms of skin exposure,

01:14:44.320 | these data also might make you think a little bit

01:14:46.540 | about whether or not you should wear short sleeves

01:14:48.120 | or long sleeves,

01:14:48.960 | whether or not you want to wear shorts or a skirt or pants.

01:14:51.780 | It's all going to depend on the context of your life

01:14:53.920 | and the social and other variables

01:14:56.300 | that are important, of course.

01:14:57.800 | I don't know each and every one of your circumstances,

01:15:00.540 | so I can't tell you to do X or Y or Z, nor would I,

01:15:05.440 | but you might take into consideration

01:15:07.180 | that it is the total amount of skin exposure

01:15:10.280 | that is going to allow you to capture more or fewer photons,

01:15:14.180 | depending on, for instance,

01:15:16.180 | if you're completely cloaked in clothing

01:15:18.000 | and you're just exposed in the hands, neck and face,

01:15:21.420 | such as I am now,

01:15:22.600 | or whether or not you're outside in shorts and a t-shirt,

01:15:25.100 | you're going to get very, very different patterns

01:15:28.340 | of biological signaling activation

01:15:30.800 | in those two circumstances.

01:15:32.160 | Many of you I'm guessing are wondering

01:15:33.900 | whether or not you should seek out UVB exposure

01:15:37.120 | throughout the entire year or only in the summer months.

01:15:39.620 | And that's sort of going to depend

01:15:41.640 | on whether or not you experience depression

01:15:45.200 | in the winter months,

01:15:46.480 | so-called seasonal affective disorder.

01:15:48.880 | Some people have mild,

01:15:49.840 | some people have severe forms of seasonal affective disorder.

01:15:52.280 | Some people love the fall and winter and the shorter days.

01:15:55.160 | They love bundling up, they love the leaves,

01:15:56.880 | they love the snow, they love the cold,

01:15:58.160 | and they don't experience those psychological lows.

01:16:00.120 | So it varies tremendously.

01:16:01.920 | And there are genetic differences

01:16:03.800 | and birthplace origin differences that relate to all this,

01:16:07.800 | but really it has to be considered on a case-by-case basis.

01:16:11.100 | I personally believe,

01:16:14.040 | and this was reinforced by the director

01:16:17.440 | of the Chronobiology Unit

01:16:19.020 | at the National Institutes of Mental Health, Samir Hattar,

01:16:21.580 | that we would all do well to get more UVB exposure

01:16:25.080 | from sunlight throughout the entire year,

01:16:27.740 | provided we aren't burning our skin

01:16:29.220 | or damaging our eyes in some way.

01:16:31.380 | In addition to that, during the winter months,

01:16:34.780 | if you do experience some drop in energy

01:16:38.020 | or increase in depression or psychological lows,

01:16:42.980 | it can be very beneficial to access a sad lamp,

01:16:47.460 | or if you don't want to buy a sad lamp,

01:16:49.300 | 'cause oftentimes they can be very expensive,

01:16:51.220 | you might do well to simply get a LED lighting panel.

01:16:55.080 | I've described one before,

01:16:56.440 | and I want to emphasize that I have no affiliation

01:16:59.340 | whatsoever to these commercial sources,

01:17:01.840 | but I've described one before and I'll describe it again,

01:17:03.680 | and we can provide a link to a couple examples of these

01:17:06.120 | in the show notes, in the show note captions, excuse me.

01:17:09.400 | This is a 932,000 lux, L-U-X,

01:17:14.240 | light source that's designed for drawing.

01:17:16.360 | It's literally a drawing box.

01:17:17.720 | It's a thin panel.

01:17:18.540 | It's about the size of a laptop.

01:17:20.480 | Very inexpensive compared to the typical sad lamp.

01:17:22.680 | I actually have one and I position on my desk all day long.

01:17:25.500 | I also have enough skylights above my desk.

01:17:27.740 | I'm fairly sensitive to the effects of light.

01:17:29.860 | So in longer days,

01:17:30.700 | I feel much better than I do in shorter days.

01:17:32.180 | I've never suffered from full-blown

01:17:33.720 | seasonal affective disorder,

01:17:35.140 | but I keep that light source on throughout the day,

01:17:38.680 | throughout the year.

01:17:39.660 | But I also make it a point to get outside

01:17:41.500 | and get sunlight early in the morning

01:17:42.780 | and several times throughout the day.

01:17:44.520 | And if it's particularly overcast outside,

01:17:47.220 | or there just doesn't seem to be a lot of sunlight

01:17:49.640 | coming through those clouds,

01:17:50.920 | I will try to look at that light source

01:17:53.500 | a little bit more each day

01:17:54.840 | in order to trigger these mechanisms.

01:17:57.380 | Now, some people may desire to get UVB exposure

01:18:00.120 | to their skin and they want to do that

01:18:02.120 | through sources other than sunlight.

01:18:03.960 | And there it's a little bit more complicated.

01:18:06.100 | There are of course, canning salons,

01:18:08.280 | which basically are beds of UVB light.

01:18:10.660 | That's really all they are.

01:18:12.160 | I've never been to one.

01:18:13.080 | I know people do frequent them

01:18:14.600 | in certain parts of the world.

01:18:16.100 | There of course, people are covering their eyes.

01:18:19.280 | They are only getting UVB exposure to their skin typically

01:18:21.740 | because the UVB exposure or intensities rather

01:18:24.880 | tends to be very, very high.

01:18:26.520 | And so you can actually damage your eyes

01:18:27.880 | if you're looking at a very, very bright

01:18:29.900 | artificial UVB source up close.

01:18:32.500 | So you really have to explore these options for yourself.

01:18:35.140 | Sunlight, of course, being the original

01:18:37.120 | and still the best way to get UVB exposure.

01:18:40.740 | So without knowing your particular circumstances,

01:18:43.320 | finances, genetics, or place of origin, et cetera,

01:18:47.340 | I can't know whether or not you need

01:18:48.820 | to use artificial sources.

01:18:49.860 | You're going to have to gauge that.

01:18:51.620 | Meanwhile, getting outside, looking at

01:18:55.220 | and getting some exposure of UVB onto your skin

01:18:59.280 | is going to be beneficial for the vast majority

01:19:01.940 | of people out there.

01:19:03.340 | And in fact, it's even going to be beneficial

01:19:05.480 | for people that are blind.

01:19:07.100 | People that are blind provided they still have eyes

01:19:10.720 | often maintain these melanopsin cells.

01:19:14.200 | So even if you're low vision or no vision,

01:19:16.200 | getting UVB exposure to your eyes can be very beneficial

01:19:19.480 | for sake of mood, hormone pathways,

01:19:22.220 | pain reduction, and so forth.

01:19:24.360 | A cautionary note, people who have retinitis pigmentosa,

01:19:28.760 | macular degeneration, or glaucoma,

01:19:31.360 | as well as people who are especially prone to skin cancers

01:19:34.680 | should definitely consult with your ophthalmologist

01:19:37.640 | and dermatologist before you start increasing

01:19:40.080 | the total amount of UVB exposure that you're getting

01:19:42.600 | from any source, sunlight or otherwise.

01:19:44.960 | There are additional very interesting

01:19:46.880 | and powerful effects of UVB light,

01:19:50.200 | in particular on immune function.

01:19:52.460 | All the organs of our body are inside our skin.

01:19:57.320 | And so information about external conditions,

01:20:00.460 | meaning the environment that we're in,

01:20:02.200 | need to be communicated to the various organs of our body.

01:20:06.360 | Some of them have more direct access

01:20:08.640 | to what's going on outside.

01:20:10.600 | So for instance, the cells in your brain

01:20:13.800 | that reside right over the roof of your mouth,

01:20:15.600 | your hypothalamus that control hormone output

01:20:17.760 | and then control the biological functions

01:20:20.560 | that we call circadian functions,

01:20:21.960 | the ones that change every 24 hours.

01:20:24.440 | Well, those are just one or two connections,

01:20:27.060 | meaning synapses away from those cells in your eye

01:20:29.760 | that perceive UVB light, excuse me.

01:20:32.500 | Other organs of your body, such as your spleen,

01:20:35.960 | which is involved in the creation of molecules and cells

01:20:39.360 | that combat infection.

01:20:41.240 | Well, those are a long ways away

01:20:42.940 | from those cells in your eye.

01:20:43.880 | And in fact, they're a long ways away from your skin.

01:20:47.240 | There are beautiful studies showing that

01:20:49.980 | if we get more UVB exposure from sunlight

01:20:53.220 | or from appropriate artificial sources,

01:20:55.980 | that spleen and immune function are enhanced.

01:21:00.800 | And there's a very logical, well-established circuit

01:21:04.280 | as to how that happens.

01:21:06.040 | Your brain actually connects to your spleen.

01:21:09.320 | Now, it's not the case that you can simply think,

01:21:12.080 | okay, spleen, turn on, release killer cells,

01:21:14.680 | go out and combat infection.

01:21:16.380 | However, UVB light arriving on the eyes

01:21:20.700 | is known to trigger activation of the neurons

01:21:23.520 | within the so-called sympathetic nervous system.

01:21:26.040 | These neurons are part of the larger thing

01:21:28.360 | that we call the autonomic nervous system,

01:21:30.120 | meaning it's below or not accessible by conscious control.

01:21:34.160 | It's the thing that controls your heartbeat,

01:21:35.560 | controls your breathing, and that also activates

01:21:38.020 | or flips on the switch of your immune system.

01:21:41.000 | When we get a lot of UVB light in our eyes,

01:21:43.560 | or I should say sufficient UVB light in our eyes,

01:21:46.880 | a particular channel, a particular set of connections

01:21:50.120 | within the sympathetic nervous system is activated,

01:21:53.220 | and our spleen deploys immune cells and molecules

01:21:57.360 | that scavenge for and combat infection.

01:22:00.300 | So if you've noticed that you get fewer colds and flus

01:22:03.860 | and other forms of illness in the summer months,

01:22:06.780 | part of that could be because of the increase in temperature

01:22:10.440 | in your environment, because typically longer days

01:22:12.440 | are associated with more warmth in your environment,

01:22:15.640 | as opposed to winter days, which are short,

01:22:17.480 | when it tends to be colder out.

01:22:19.560 | Well, that's true, but it's also the case

01:22:23.960 | the people around you have fewer colds and flus

01:22:26.440 | and that you will get infected with fewer colds and flus

01:22:29.640 | and other infections, because if those infections,

01:22:34.480 | whether or not they're bacterial or viral,

01:22:36.880 | arrive in your body, right, if you inhale them

01:22:39.380 | or they get into your mouth or on your skin,

01:22:41.980 | your spleen meets those infections with a greater output.

01:22:45.480 | In other words, the soldiers of your immune system,

01:22:47.540 | the chemicals and cell types of your immune system

01:22:50.200 | that combat infection are in a more ready deployed stance,

01:22:55.200 | if you will.

01:22:56.440 | If you want to know more about the immune system

01:22:58.120 | and immune function, I did an entire episode

01:23:00.000 | about the immune system and the brain in a,

01:23:02.660 | you can find that at hubermanlab.com.

01:23:04.840 | We talk about cytokines, we talk about killer cells,

01:23:06.820 | B cells, T cells, et cetera, a lot of detail there.

01:23:09.480 | So we often think about the summer months

01:23:11.720 | and the spring months as fewer infections floating around,

01:23:15.320 | but in fact, there aren't fewer infections floating around.

01:23:18.840 | We are simply better at combating those infections

01:23:21.460 | and therefore there's less infection floating around.

01:23:25.080 | So we are still confronted with a lot of infections.

01:23:27.640 | We're just able to combat them better.

01:23:29.920 | What does this mean in terms of a tool?

01:23:31.360 | What it means is that during the winter months,

01:23:33.840 | we should be especially conscious of accessing UVB light

01:23:38.560 | to enhance our spleen function,

01:23:41.320 | to make sure that our sympathetic nervous system

01:23:43.700 | is activated to a sufficient level

01:23:46.160 | to keep our immune system deploying all those killer T cells

01:23:49.520 | and B cells and cytokines

01:23:51.100 | so that when we encounter the infections,

01:23:52.860 | as we inevitably will, right,

01:23:54.740 | we're constantly being bombarded with potential infections

01:23:57.740 | that we can combat those infections well.

01:24:00.240 | And as just a brief aside,

01:24:01.980 | but I should mention a brief aside that's related

01:24:04.280 | to tens of thousands of quality studies.

01:24:07.240 | It is well known that wound healing is faster

01:24:10.540 | when we are getting sufficient UVB exposure.

01:24:13.900 | Typically that's associated with the longer days

01:24:16.340 | of spring and summer.

01:24:17.680 | It is known that turnover of hair cells,

01:24:21.400 | the very cells that give rise to hair cells

01:24:23.580 | are called stem cells.

01:24:24.420 | They've lived in little so-called niches in our skin

01:24:27.040 | with these hair stem cells

01:24:28.560 | and your hair grows faster in longer days.

01:24:31.000 | That too is triggered by UVB exposure,

01:24:34.440 | not just to the skin, but to the eyes.

01:24:37.520 | That's right.

01:24:38.440 | There was a study published in the Proceedings

01:24:40.720 | of the National Academy of Sciences a couple of years ago

01:24:44.120 | that showed that the exposure of those melanopsin ganglion

01:24:47.460 | cells in your eyes is absolutely critical

01:24:49.960 | for triggering the turnover of stem cells

01:24:53.320 | in both the skin and hair.

01:24:56.340 | And also it turns out in nails.

01:24:58.640 | So if you've noticed that your skin, your hair

01:25:01.240 | and your nails look better and turn over more,

01:25:03.560 | meaning grow faster in longer days,

01:25:06.560 | that is not a coincidence.

01:25:08.040 | That is not just your perception.

01:25:09.780 | In fact, hair grows more, skin turns over more,

01:25:13.520 | meaning it's going to look more youthful.

01:25:14.880 | You're going to essentially remove older skin cells

01:25:18.200 | and replace them with new cells.

01:25:20.320 | And all the renewing cells and tissues of our body

01:25:23.660 | are going to proliferate, are going to recreate themselves

01:25:26.800 | more when we're getting sufficient UVB light to our eyes

01:25:30.240 | and also to our skin.

01:25:31.960 | And so while some of you may think of light therapies,

01:25:36.200 | such as red light therapies or UVB therapies

01:25:38.560 | as kind of new agey or just biohacking,

01:25:41.000 | again, a phrase I don't particularly like,

01:25:42.920 | this notion of biohacking,

01:25:44.200 | 'cause it implies using one thing for a purpose

01:25:47.440 | that it was never intended to have.

01:25:49.700 | Well, it turns out that UVB exposure and red light,

01:25:54.240 | as we'll soon see, is a very potent form

01:25:57.520 | of increasing things like wound healing and skin health

01:26:00.160 | for very logical mechanistically backed reasons.

01:26:04.660 | So while I can't account for everything

01:26:07.480 | that's being promoted out there in terms of this light source

01:26:09.860 | will help your skin look more youthful

01:26:11.280 | or will help heal your scars,

01:26:13.420 | the mechanistic basis for light having those effects

01:26:17.560 | makes total sense.

01:26:19.160 | But what you should consider, however,

01:26:21.240 | is that if the particular light therapy

01:26:23.720 | that you're considering involves very local application

01:26:27.580 | rather than illuminating broad swaths of skin,

01:26:32.560 | and if it has no involvement with the eyes,

01:26:35.000 | meaning there's no delivery of UVB or red light

01:26:38.860 | or the other light therapy to the eyes,

01:26:41.400 | it's probably not going to be as potent a treatment

01:26:44.960 | as would a more systemic activation

01:26:48.120 | of larger areas of skin and the eyes.

01:26:51.080 | Now, again, a cautionary note,

01:26:52.800 | I don't want people taking technologies

01:26:54.480 | that were designed for local application

01:26:56.500 | and beaming those into the eyes.

01:26:58.260 | That could be very, very bad and damaging

01:27:00.040 | to your retinal and other tissues.

01:27:02.540 | Certainly wouldn't want you taking bright light

01:27:05.280 | of very high intensity of any kind

01:27:07.440 | and getting cavalier about that.

01:27:09.560 | Typically the local illumination of say a wound

01:27:12.940 | or a particular patch of acne

01:27:14.360 | or some other form of skin treatment

01:27:17.020 | involves very high intensity light.

01:27:18.840 | And if the intensity is too high,

01:27:20.440 | you can actually damage that skin.

01:27:22.400 | And so, as we'll talk about in a few moments,

01:27:24.880 | most of those therapies for modifying skin

01:27:27.380 | involve actually burning off a small,

01:27:30.360 | very thin layer at the top of the epidermis

01:27:33.480 | in efforts to trigger the renewal

01:27:35.640 | or the activation of stem cells

01:27:37.000 | that will replenish that with new cells.

01:27:39.860 | So there's a fine line to be had

01:27:42.800 | between light therapies that are very localized and intense,

01:27:45.960 | which are designed to damage skin

01:27:48.140 | and cause reactivation of new stem cells,

01:27:52.500 | whether or not it's hair cells or skin cells, et cetera,

01:27:54.740 | versus systemic activation

01:27:56.480 | across broad swaths of skin in the eyes.

01:27:58.340 | You really have to consider this on a case by case basis,

01:28:00.860 | but at least for now,

01:28:02.740 | just consider that increases in hormones,

01:28:05.900 | reduction in pain by way of increases in enkephalin

01:28:10.660 | and other endogenous opioids,

01:28:12.700 | improving immune status by activating the spleen

01:28:15.700 | and so on and so on,

01:28:17.360 | really are all the downstream consequence

01:28:19.540 | of illuminating large swaths of skin

01:28:21.900 | and making sure that those neurons within the eye

01:28:23.940 | get their adequate UVB exposure

01:28:26.240 | or other light wavelength exposure,

01:28:28.240 | not simply beaming a particular wavelength of light

01:28:31.340 | at a particular location on the body

01:28:32.960 | and hoping that that particular illumination

01:28:35.360 | at a particular location on the body

01:28:37.100 | is going to somehow change the biology at that location.

01:28:40.460 | Our biology just really doesn't work that way.

01:28:43.320 | It's possible, but in general,

01:28:45.240 | systemic effects through broad scale illumination

01:28:48.420 | and illumination to the eye

01:28:49.700 | combined with local treatments

01:28:51.560 | are very likely to be the ones that have the most success.

01:28:54.340 | Now I'd like to shift our attention

01:28:55.680 | to the effects of light on mood more specifically.

01:28:57.980 | We talked about this

01:28:58.820 | in terms of seasonal affective disorder,

01:29:00.680 | but many of us don't suffer from seasonal affective disorder.

01:29:03.380 | So I'd like to drill a little deeper

01:29:04.820 | into how light impacts mood.

01:29:07.620 | And here, I want to, again,

01:29:10.540 | paraphrase the statements of Dr. Samir Hattar

01:29:14.460 | at the National Institutes of Mental Health.

01:29:16.780 | I should mention the director of the Chronobiology Unit

01:29:18.940 | at the National Institutes of Mental Health

01:29:20.660 | and perhaps one of the top one to two to three world experts

01:29:25.660 | in how light can impact mood, appetite,

01:29:28.180 | circadian rhythms, and so forth.

01:29:29.780 | Samir stated on the podcast

01:29:33.040 | and he said in various other venues as well,

01:29:36.220 | that getting as much UVB light in our eyes

01:29:39.860 | and on our skin in the early day and throughout the day

01:29:42.380 | as a safely possible is going to be beneficial for mood.

01:29:45.500 | There's also another time of day,

01:29:48.100 | or rather I should say a time of night

01:29:49.780 | in which UVB can be leveraged in order to improve mood,

01:29:54.400 | but it's actually the inverse

01:29:55.900 | of everything we've been talking about up until now.

01:29:58.500 | We have a particular neural circuit

01:30:01.740 | that originates with those melanopsin cells in our eye

01:30:04.900 | that bypass all the areas of the brain

01:30:07.220 | associated with circadian clocks.

01:30:09.140 | So everything related to sleep and wakefulness

01:30:11.540 | that's specifically dedicated to the pathways

01:30:14.760 | involving the release of molecules like dopamine,

01:30:16.980 | the neuromodulator that's associated with motivation,

01:30:19.900 | with feeling good,

01:30:22.120 | with feeling like there's possibility in the world

01:30:24.540 | and so on and so forth.

01:30:25.760 | And other molecules as well, including serotonin

01:30:28.060 | and some of those endogenous opioids

01:30:29.700 | that we talked about before.

01:30:31.100 | That particular pathway involves a brain structure

01:30:34.340 | called the perihabenular nucleus.

01:30:36.700 | The perihabenular nucleus gets input

01:30:39.700 | from the cells in the eye that respond to UVB light

01:30:43.420 | and frankly to bright light of other wavelengths as well.

01:30:46.740 | 'Cause as you recall, if a light is bright enough,

01:30:49.440 | even if it's not UV or blue light,

01:30:51.340 | it can activate those cells in the eye.

01:30:53.820 | Those cells in the eye communicate

01:30:55.340 | to the perihabenular nucleus.

01:30:57.380 | And as it turns out, if this pathway is activated

01:31:01.060 | at the wrong time of each 24 hour cycle,

01:31:04.740 | mood gets worse.

01:31:07.060 | Dopamine output gets worse.

01:31:09.740 | Molecules that are there specifically to make us feel good

01:31:13.180 | actually are reduced in their output.

01:31:16.080 | So while UVB exposure in the morning and throughout the day

01:31:20.420 | is going to be very important for elevating

01:31:24.380 | and maintaining elevated mood,

01:31:26.500 | avoiding UVB light at night is actually a way

01:31:30.820 | in which we can prevent activation of this

01:31:34.900 | eye to perihabenular pathway that can actually

01:31:37.460 | turn on depression.

01:31:38.900 | To be very direct and succinct about this,

01:31:41.640 | avoid exposure to UVB light from artificial sources

01:31:44.940 | between the hours of 10 PM and 4 AM.

01:31:48.460 | And if you're somebody who suffers from low mood

01:31:51.780 | and overall has a kind of mild depression

01:31:54.660 | or even severe depression, of course,

01:31:56.460 | please see a psychiatrist, see a trained psychologist,

01:31:59.340 | get that treated.

01:32:00.940 | But you would do especially well to avoid UVB exposure

01:32:05.940 | from artificial sources, not just from 10 PM to 4 AM,

01:32:09.560 | but really be careful about getting too much exposure

01:32:12.020 | to UVB, even in the late evening.

01:32:14.380 | So 8 PM perhaps to 4 AM.

01:32:17.180 | I can't emphasize this enough that if you view UVB light,

01:32:21.740 | you activate those neurons in your eye very potently.

01:32:24.540 | And if those cells communicate to the perihabenular nucleus,

01:32:28.060 | which they do, you will truncate or reduce

01:32:30.700 | the amount of dopamine that you release.

01:32:33.360 | So if you want to keep your mood elevated,

01:32:36.140 | get a lot of light, UVB light throughout the day.

01:32:38.880 | And at night, really be cautious about getting UVB exposure

01:32:42.840 | from artificial sources.

01:32:44.120 | Now let's say you're somebody who has no issues with mood.

01:32:46.940 | You're just the happiest person all year long,

01:32:49.500 | or maybe you just have subtle variations in your mood.

01:32:52.520 | You feel great about that.

01:32:53.820 | Turns out that you still want to be very careful

01:32:57.900 | about light exposure between the hours of 10 PM or so

01:33:02.040 | and 4 AM.

01:33:02.880 | In fact, even during sleep.

01:33:04.980 | There's a recent study that just came out

01:33:06.800 | in the proceeds of the National Academy of Sciences.

01:33:09.720 | And it's entitled light exposure during sleep

01:33:12.700 | in pairs cardiometabolic function.

01:33:14.980 | This is a very interesting study

01:33:17.660 | where they took human subjects, young adults,

01:33:20.180 | and having them sleep in rooms

01:33:22.620 | that had different lighting conditions,

01:33:24.000 | either dim light or slightly bright light.

01:33:27.880 | Now, many people can't fall asleep in brightly lit rooms.

01:33:30.440 | So they acknowledge this.

01:33:32.240 | These were not very brightly lit rooms.

01:33:33.920 | These were rooms that had just a little bit

01:33:36.220 | of overhead room lighting, a hundred lux,

01:33:39.200 | which is not very bright at all.

01:33:41.240 | Or they had them sleep in a room that had very dim light,

01:33:43.880 | which is less than three lux.

01:33:45.760 | If you want to get a sense of how bright three lux is

01:33:49.120 | versus a hundred lux,

01:33:50.720 | I would encourage you to download the free app Light Meter.

01:33:53.860 | I have no relationship to the app.

01:33:55.380 | It's a pretty cool app.

01:33:56.220 | However, I've used it for a long time

01:33:57.540 | where you can basically point your phone

01:34:00.040 | at a particular light source, sun or otherwise,

01:34:02.320 | and you just press the button.

01:34:03.240 | It'll give you an approximate readout of lux,

01:34:05.560 | which is the light intensity that the phone happens

01:34:08.760 | to be staring out at at that location.

01:34:10.900 | It's not exact, but it's a pretty good back

01:34:14.300 | of the envelope measure of light intensity.

01:34:17.400 | So these subjects were either sleeping in a very dim room,

01:34:20.360 | three lux is very, very dim,

01:34:22.160 | or a somewhat dim room, a hundred lux.

01:34:25.900 | In this study, they measured things like melatonin levels.

01:34:29.180 | They looked at heart rate.

01:34:30.920 | They looked at measures of insulin and glucose management.

01:34:35.880 | Now, in previous episodes,

01:34:38.020 | I've talked about how glucose blood sugar

01:34:40.400 | is regulated by insulin

01:34:42.380 | because you don't want your glucose levels to be too high,

01:34:44.820 | hyperglycemia or too low.

01:34:46.580 | Hypoglycemia and the hormone insulin is involved

01:34:49.140 | in sequestering and shuttling glucose in the bloodstream.

01:34:52.480 | Basically how well you manage glucose in the bloodstream

01:34:55.360 | can be indirectly measured by your insulin levels.

01:34:58.460 | And it's well-known that sleep deprivation

01:35:01.440 | can disrupt glucose regulation by insulin.

01:35:06.440 | However, in this study,

01:35:08.260 | subjects were sleeping the whole night through.

01:35:10.120 | It just so happens that some of the subjects

01:35:11.720 | were sleeping in this very dimly lit room, three lux,

01:35:14.120 | and other subjects were sleeping

01:35:15.360 | in a somewhat dimly lit room, a hundred lux.

01:35:19.720 | What's incredible about this study

01:35:21.680 | is that both rooms were sufficiently dim

01:35:24.160 | that melatonin levels were not altered in either case.

01:35:27.460 | This is really key.

01:35:28.300 | It's not as if one group experienced a lot of bright light

01:35:31.460 | through their eyelids and others did not.

01:35:33.600 | Melatonin levels were not disrupted.

01:35:35.520 | And given how potently light can inhibit melatonin,

01:35:38.240 | this speaks to the fact that this very dim condition

01:35:41.440 | of three lux and the somewhat dim condition of a hundred lux

01:35:44.840 | was not actually perceived by the subjects,

01:35:48.040 | nor was it disrupting these hormone pathways.

01:35:50.720 | They also looked at glucose responses.

01:35:53.240 | They had people essentially take a fasting glucose test

01:35:56.440 | in different conditions.

01:35:57.360 | I won't go into all the details,

01:35:58.920 | but here's what they found.

01:36:00.380 | In healthy adults,

01:36:01.920 | even just one night of sleeping

01:36:04.400 | in a moderately lit environment,

01:36:06.880 | this hundred lux environment,

01:36:08.320 | caused changes, increases in nighttime heart rate,

01:36:12.600 | which means that the sympathetic nervous system

01:36:14.400 | was overly active as compared to people that slept

01:36:17.080 | in a completely dark or in a very, very dimly lit room,

01:36:20.860 | decreases in heart rate variability.

01:36:23.460 | And here I should point out that heart rate variability

01:36:25.720 | or HRV is a good thing.

01:36:27.420 | We want heart rate variability.

01:36:28.660 | So they saw increases in heart rate,

01:36:30.340 | decreases in heart rate variability,

01:36:32.440 | and increases in next morning insulin resistance,

01:36:36.320 | which is an indication that glucose management is suffering.

01:36:40.740 | So this is powerful.

01:36:43.280 | The results of this study essentially indicate

01:36:45.840 | that even just one night of sleeping the whole night through

01:36:49.120 | in a dimly lit environment is disrupting the way

01:36:52.460 | that our autonomic nervous system is functioning,

01:36:54.920 | altering so-called autonomic tone,

01:36:57.520 | making us less relaxed is probably the best way

01:37:00.240 | to describe it.

01:37:01.480 | Even though we are asleep,

01:37:03.080 | disrupting the way that our cardio metabolic function

01:37:06.820 | operates such that we have lower heart rate variability

01:37:09.820 | and increased insulin resistance.

01:37:12.880 | This is not a good thing for any of us to experience.

01:37:15.640 | So while we've mainly been talking about the positive

01:37:18.240 | effects of UVB light and other forms of light.

01:37:21.160 | Now we have two examples,

01:37:22.920 | one from the work of Hotar and colleagues showing

01:37:25.600 | that UVB exposure via the perihabenula can diminish

01:37:29.480 | the output of dopamine and other molecules that make us

01:37:32.580 | feel good if that UVB exposure is in the middle

01:37:34.840 | of the night or late evening.

01:37:36.760 | And now we have yet another study performed in this case

01:37:39.800 | in humans indicating that even if we fall asleep

01:37:43.160 | and sleep the whole night through,

01:37:44.560 | if the room that we're sleeping in has too many locks,

01:37:47.520 | too much light energy,

01:37:48.840 | that light energy is no doubt going through the eyelids,

01:37:51.820 | which it can activating the particular cells in the eye

01:37:55.600 | that trigger an increase in sympathetic nervous system

01:37:59.160 | activation and disrupting our metabolism.

01:38:02.340 | And this study rests on a number of other recent studies

01:38:05.640 | published in Cell, which is a superb journal

01:38:07.920 | and other journals showing that during the course

01:38:10.180 | of a healthy deep night's sleep,

01:38:13.040 | our body actually transitions through various forms

01:38:15.400 | of metabolic function.

01:38:16.760 | We actually experience ketosis like states.

01:38:20.400 | We experience gluconeogenesis.

01:38:22.840 | We experience different forms of metabolism associated

01:38:25.640 | with different stages of sleep.

01:38:27.200 | Not something that we're going into in depth

01:38:29.040 | in this podcast, we will in a future podcast.

01:38:31.760 | What this study shows is that light exposure,

01:38:34.840 | even in sleep is disrupting our autonomic,

01:38:38.060 | in this case, the sympathetic arm

01:38:39.360 | of the autonomic nervous system in ways

01:38:41.380 | that are disrupting metabolism probably in sleep,

01:38:44.240 | but certainly outside of sleep.

01:38:46.240 | So that we wake up and have our first meal of the day,

01:38:48.400 | or even if you're intermittent fasting,

01:38:49.680 | you eat that first meal of the day.

01:38:51.280 | If your sleep is taking place in an environment

01:38:54.280 | that's overly illuminated,

01:38:56.560 | well, that's disrupting your cardiac function

01:38:59.260 | and your metabolism.

01:39:00.680 | I've been talking a lot about UVB light,

01:39:02.440 | which is short wavelength light.

01:39:03.940 | So UV light, blue light, maybe even some blue green light.

01:39:07.140 | That's going to be short wavelength light.

01:39:08.660 | Now I'd like to shift our attention

01:39:09.760 | to the other end of the spectrum,

01:39:11.100 | meaning the light spectrum,

01:39:12.320 | to talk about red light and infrared light,

01:39:14.320 | which is long wavelength light.

01:39:16.220 | Many so-called low-level light therapies,

01:39:19.920 | the acronym is LLLT, low-level light therapies,

01:39:23.960 | involve the use of red light and infrared light.

01:39:27.560 | Sometimes low-level light therapies involve the use of UVB,

01:39:31.080 | but more often than not these days when we hear LLLT,

01:39:34.200 | low-level light therapy,

01:39:35.720 | it's referring to red light

01:39:37.500 | and near infrared light therapies.

01:39:39.980 | Low-level light therapies have been shown to be effective

01:39:44.560 | for a huge number of biological phenomenon

01:39:47.600 | and medical treatments.

01:39:49.380 | I can't summarize all of those now.

01:39:50.900 | It would take me many, many hours.

01:39:52.740 | It would be an effective episode for curing insomnia,

01:39:55.340 | but it wouldn't inform you properly

01:39:57.340 | about the use of light for your health.

01:39:59.760 | Rather, I'd like to just emphasize

01:40:01.340 | some of the top contour of those studies

01:40:03.520 | and point out that, for instance,

01:40:06.000 | low-level light therapy with infrared light

01:40:08.120 | has been shown to be effective for the treatment of acne

01:40:10.920 | and other sorts of skin lesions.

01:40:13.000 | There've been some really nice studies actually

01:40:15.160 | where they use subjects as their own internal control.

01:40:17.960 | So people, believe it or not,

01:40:19.120 | agreed to have half of their face illuminated

01:40:21.620 | with red light or near infrared light

01:40:23.880 | and the other half of their face serve as a control

01:40:26.000 | and to do that for several weeks at a time.

01:40:28.300 | And you can see pretty impressive reductions

01:40:31.060 | in skin lesions, reductions in scars from acne,

01:40:35.180 | and reduction in acne lesions themselves,

01:40:38.180 | meaning the accumulation of new acne cysts

01:40:40.980 | with low-level light therapy using red light

01:40:43.200 | and infrared light.

01:40:44.560 | Sometimes, however, there is a resistance of that acne

01:40:49.240 | to the low-level light therapy,

01:40:50.580 | such that people will get an initial improvement

01:40:52.740 | and then it'll go away despite continuing the treatment.

01:40:55.660 | So you're probably asking, or at least you should be asking,

01:40:58.220 | how is it that shining red light on our skin

01:41:00.740 | can impact things like acne and wound healing, et cetera?

01:41:04.600 | Well, to understand that,

01:41:06.100 | we have to think back to the beginning of the episode

01:41:08.340 | where I described how long wavelength light,

01:41:10.700 | such as red light and near infrared light,

01:41:13.060 | which is even longer than red light,

01:41:15.120 | can pass through certain surfaces, including our skin.

01:41:19.140 | So our skin has an epidermis, which is on the outside,

01:41:21.780 | and the dermis, which is in the deeper layers.

01:41:24.400 | Red light and infrared light can pass down

01:41:27.100 | into the deeper layers of our skin

01:41:29.020 | where it can change the metabolic function

01:41:31.740 | of particular cells.

01:41:32.860 | So let's just take acne as an example.

01:41:35.600 | Within the dermis, the deep layers of our skin,

01:41:37.900 | we have what are called sebaceous glands

01:41:39.700 | that actually make the oil that is present in our skin.

01:41:43.700 | Those sebaceous glands are often nearby hair follicles.

01:41:46.700 | So if you've ever had an infected hair follicle,

01:41:50.100 | that's not a coincidence

01:41:51.460 | that hair follicles tend to get infected.

01:41:53.100 | Part of it is because there's actually a portal down

01:41:56.220 | and around the hair follicle,

01:41:57.380 | but the sebaceous gland is where the oil is created

01:42:00.500 | that is going to give rise to, for instance, acne lesions.

01:42:03.740 | Also in the dermis, in the deep layers of the skin,

01:42:06.900 | are the melanocytes.

01:42:07.900 | They're not just in the epidermis,

01:42:08.920 | they're also in the deeper layers of the skin.

01:42:11.780 | And you have the stem cells that give rise

01:42:14.740 | to additional skin cells.

01:42:16.820 | If the top layers of the epidermis are damaged,

01:42:19.180 | those stem cells can become activated.

01:42:21.260 | And you also have the stem cells

01:42:23.520 | that give rise to hair follicles.

01:42:25.340 | So by shining red light or near infrared light

01:42:29.620 | on a localized patch of skin,

01:42:31.580 | provided that red light is not of such high intensity

01:42:34.940 | that it burns the skin,

01:42:36.500 | but is of sufficient intensity

01:42:38.520 | that provides just a little bit of damage

01:42:41.060 | to the upper layers of the skin, the epidermis,

01:42:43.820 | and that it triggers certain biological pathways

01:42:47.180 | within the cells of the sebaceous gland

01:42:49.500 | and the stem cells within the hair cell niche

01:42:52.460 | and the stem cells in skin,

01:42:54.020 | what happens is the top layers of the skin

01:42:56.660 | are basically burned off by a very low level of burn

01:43:00.460 | and/or the cells in the deeper layer

01:43:02.420 | start to churn out new cells

01:43:03.900 | which go and rescue the lesion,

01:43:07.380 | essentially clear out the lesion

01:43:09.620 | and replace that lesion with healthy skin cells.

01:43:12.020 | This does work in the context of wound healing,

01:43:17.420 | getting scars to disappear.

01:43:19.020 | It also works to remove certain patches of pigmentation.

01:43:22.980 | There are sometimes cases where people will get

01:43:24.840 | a red blotchiness due to certain skin conditions

01:43:28.580 | or some darker pigmentation that they want removed

01:43:31.340 | or that they need removed

01:43:32.560 | because it's a potential skin cancer threat.

01:43:36.020 | Now, how is red light actually doing it

01:43:37.860 | within the cells of the sebaceous gland,

01:43:39.540 | the stem cells, et cetera?

01:43:41.000 | Well, long wavelength light

01:43:43.180 | can actually get deep into the skin.

01:43:45.180 | I mentioned that before,

01:43:46.000 | but can also get into individual cells

01:43:49.780 | and can access the so-called organelles,

01:43:51.700 | which I described at the beginning of the episode.

01:43:53.340 | In particular, they can access the mitochondria,

01:43:55.800 | which are responsible for producing ATP.

01:43:58.500 | Now, the simple way to think about this

01:44:00.540 | for sake of this discussion is that as cells age,

01:44:05.540 | and in particular in very metabolically active cells,

01:44:09.120 | they accumulate what are called ROSs,

01:44:12.780 | reactive oxygen species.

01:44:14.980 | And as reactive oxygen species go up,

01:44:18.780 | ATP energy production in those cells tends to go down.

01:44:22.340 | It's a general statement,

01:44:23.400 | but it's a general statement that in most cases is true.

01:44:27.180 | There are some minor exceptions that don't concern us

01:44:29.880 | that have to do with cell types

01:44:31.340 | different than the ones that I'm talking about now.

01:44:33.540 | So the way to think about this is that red light

01:44:35.420 | passes into the deeper layers of the skin,

01:44:37.980 | activates mitochondria, which increases ATP,

01:44:40.940 | and directly or indirectly

01:44:42.720 | reduces these reactive oxygen species.

01:44:45.060 | These reactive oxygen species are not good.

01:44:48.220 | We don't want them.

01:44:49.360 | They cause cellar damage, cellar death,

01:44:52.340 | and for the most part,

01:44:53.820 | just inhibit the way that our cells work.

01:44:56.660 | So if you've heard of red light

01:44:58.560 | or near infrared light therapies designed to heal skin

01:45:02.540 | or improve skin quality or remove lesions

01:45:05.020 | or get rid of scars or unwanted pigmentation,

01:45:07.860 | that is not pseudoscience.

01:45:10.020 | That is not woo science.

01:45:12.340 | That is grounded in the very biology

01:45:14.580 | of how light interacts with mitochondria

01:45:16.440 | and reactive oxygen species.

01:45:18.360 | Some of you may also find it interesting to note

01:45:20.540 | that some of the cream-based treatments

01:45:22.740 | for acne, for instance, like retinoic acid, Retin-A,

01:45:26.600 | is actually a derivative of vitamin A

01:45:30.060 | and the pathway involving retinoic acid and vitamin A,

01:45:33.720 | believe it or not, is very similar

01:45:35.900 | to the natural biological pathway

01:45:38.520 | by which photopigments in the eye convert light information

01:45:41.980 | into biological changes within those cells.

01:45:44.640 | So the key point here is that light is activating

01:45:48.380 | particular pathways in cells

01:45:50.260 | that can either drive death of cells

01:45:52.820 | or can make those cells essentially younger

01:45:55.700 | by increasing ATP by way of improving mitochondrial function.

01:46:00.540 | And in recent years,

01:46:01.800 | there've been some just beautiful examples

01:46:04.340 | that exist not only in the realm of skin biology,

01:46:07.700 | but in the realm of neurobiology,

01:46:10.180 | whereby red light and near infrared light

01:46:12.800 | can actually be used to enhance the function of the cells

01:46:15.620 | that, for instance, allow us to see better

01:46:17.780 | and indeed cells that allow us to think better.

01:46:20.600 | So now I'd like to review those data

01:46:22.320 | because not only are they interesting in their own right,

01:46:25.660 | but they also point to some very interesting

01:46:28.500 | and powerful application of low cost or zero cost tools

01:46:31.900 | that we can use to improve our vision.

01:46:34.460 | If you are somebody who's interested in the use of red light

01:46:37.020 | or near infrared light, so-called LLLT,

01:46:40.060 | low level light therapies for treatment of dermatologic

01:46:43.640 | issues, so anything related to skin,

01:46:45.920 | I will include a link to a excellent set of reviews.

01:46:49.160 | The first one is light emitting diodes in dermatology,

01:46:52.240 | a systematic review of randomized controlled trials.

01:46:55.220 | That one includes review of a very large number of studies

01:46:58.480 | came out just a few years ago in 2018,

01:47:00.840 | and I think is very clearly and cleanly laid out

01:47:03.900 | for anyone to access.

01:47:05.220 | You can see the degree of effects of red light,

01:47:07.120 | for instance, on treatment of acne or scarring, et cetera.

01:47:09.360 | And I'll also provide a link to another review,

01:47:12.040 | which is low level light therapy in skin,

01:47:14.320 | stimulating healing and restoring.

01:47:16.080 | So for those of you that are interested,

01:47:17.760 | again, in dermatologic issues and the kind of restoring

01:47:21.260 | youthfulness and the kind of general themes of anti-aging

01:47:25.200 | and longevity and how red light therapies can be used

01:47:27.880 | for that, I will encourage you to take a look

01:47:30.280 | at those reviews.

01:47:31.360 | What you're going to find is that rarely, if ever,

01:47:35.240 | is there a study looking at whole body red light illumination

01:47:38.840 | for sake of treating and improving skin.

01:47:41.880 | And I mentioned this because I get a lot of questions

01:47:44.320 | about infrared sauna and global illumination with red lights.

01:47:49.320 | We'll talk more about cases where global illumination

01:47:52.520 | of your whole body or your whole face with red lights

01:47:55.260 | might be useful.

01:47:56.560 | But in terms of infrared sauna,

01:47:58.400 | I've mentioned on this podcast before,

01:47:59.880 | and I will certainly go deeper on this

01:48:01.400 | in an upcoming episode,

01:48:02.400 | all about the use of heat and temperature

01:48:04.840 | for augmenting our biology.

01:48:06.940 | But in general, infrared saunas don't get hot enough

01:48:11.840 | temperature wise in order to trigger some

01:48:14.880 | of the important effects on growth hormone

01:48:16.760 | and heat shock proteins and some of the other things

01:48:18.760 | that sauna has been shown to be excellent for.

01:48:21.960 | That's a general statement.

01:48:22.900 | I realized there are some infrared saunas

01:48:24.520 | that do get hot enough.

01:48:26.400 | There are very few data on the use of whole body illumination

01:48:30.760 | with infrared saunas.

01:48:32.580 | They really point to any specific

01:48:35.240 | mechanistically supported effects.

01:48:37.380 | Almost all the positive effects that you're going to see

01:48:39.560 | of red light and low level light therapies,

01:48:41.860 | certainly the ones discussed in the reviews

01:48:43.320 | that I just mentioned are going to be the consequence

01:48:46.800 | of very directed illumination of particular patches of skin

01:48:50.700 | that are seeking repair,

01:48:52.140 | that people are seeking the repair of.

01:48:54.240 | So again, I don't want to disparage infrared saunas,

01:48:58.020 | but in general, they don't get hot enough

01:48:59.360 | to trigger most of the positive effects

01:49:01.060 | that sauna have been demonstrated to have.

01:49:03.860 | And it's unclear at all as to whether or not

01:49:07.000 | they can enhance skin quality, youthfulness,

01:49:09.320 | restore top layers of skin that are damaged,

01:49:14.160 | repair acne, et cetera.

01:49:15.720 | So more on heat saunas and infrared saunas

01:49:18.080 | in their comparison in an upcoming episode.

01:49:20.680 | So let's talk about a clear set of examples

01:49:23.560 | where red light and near infrared light

01:49:26.760 | have been shown to have positive effects on our health.

01:49:30.360 | And these are the data that I referred to

01:49:32.400 | at the beginning of the episode

01:49:33.760 | from Dr. Glenn Jeffrey at University College London,

01:49:37.020 | who again is a longstanding member

01:49:40.600 | of the neuroscience community

01:49:41.680 | working on visual neuroscience

01:49:43.220 | and who over the last decade or so

01:49:45.400 | has really emphasized the exploration of red light

01:49:48.520 | and near infrared light for restoration

01:49:51.520 | of neuronal function as we age.

01:49:53.980 | This is absolutely critical.

01:49:55.200 | We know that we don't accumulate many new brain cells

01:49:59.400 | as we get older.

01:50:00.240 | And in some areas of our nervous system,

01:50:02.220 | such as our neural retina,

01:50:04.000 | which is the part of our eye that's responsible

01:50:06.060 | for translating light information to electrical signals

01:50:08.480 | so that we can see we don't get any new cells

01:50:12.140 | after the time in which we were born.

01:50:13.980 | So the ability to keep our neurons healthy

01:50:16.560 | is extremely important for our visual system,

01:50:19.400 | extremely important for our hippocampus,

01:50:22.140 | an area of the brain involved in memory.

01:50:24.260 | And I should just mention

01:50:25.980 | that even if people don't get Alzheimer's,

01:50:28.040 | there's always going to be some degree

01:50:29.980 | of age-related dementia.

01:50:31.860 | Sadly, nobody is as cognitively sharp

01:50:35.660 | in the years before they die

01:50:36.960 | as they are 20 years before that.

01:50:39.200 | It's just never the case.

01:50:40.320 | We're all getting worse at thinking,

01:50:42.480 | feeling, perceiving, et cetera.

01:50:44.480 | The question is how quickly we are getting worse.

01:50:46.680 | So any mechanism by which we can preserve

01:50:49.560 | or reverse neuronal function

01:50:51.600 | turns out to be immensely beneficial.

01:50:54.360 | The Jeffrey Lab has published two studies in recent years

01:50:58.960 | on humans that looked directly, no pun intended,

01:51:03.520 | at how red light and near infrared light

01:51:05.800 | can improve visual function.

01:51:08.300 | I'm going to describe the parameters of those studies

01:51:10.320 | and then I'm going to describe what they found exactly.

01:51:13.220 | The mechanistic motivation for these studies,

01:51:17.600 | again, traces back to this effect of light on mitochondria.

01:51:22.480 | So to go a little bit deeper into that mechanism

01:51:24.240 | just briefly so that you can frame any potential protocol

01:51:28.120 | that you would develop.

01:51:29.400 | When light arrives on cells, including neurons,

01:51:35.600 | that light can penetrate into the cells

01:51:37.600 | if it's at the appropriate wavelength.

01:51:38.980 | Red light can do that, it can get into cells,

01:51:40.960 | it can access the mitochondria, it can increase ATP.

01:51:44.000 | In general, anytime ATP is doing its thing

01:51:47.840 | to increase energy in cells,

01:51:50.060 | it's involving this thing called cytochrome C,

01:51:54.440 | which is an oxidase.

01:51:55.600 | Anytime you hear ACE, A-S-E in biology,

01:51:58.720 | it's going to be an enzyme.

01:51:59.800 | It's involved in some process of degrading a molecule

01:52:02.920 | and creating another molecule typically.

01:52:05.200 | So ATP in cytochrome C is going to give you ATP.

01:52:08.440 | Now that's a great thing, but it creates a by-product.

01:52:13.300 | It breaks things down such that you get these ROSs,

01:52:16.080 | these reactive oxygen species.

01:52:18.080 | And those reactive oxygen species,

01:52:19.860 | for those of you that want to know,

01:52:21.160 | are involved in things like redox signaling

01:52:23.860 | and reactive oxygen species actually change

01:52:27.280 | which genes are made in a cell.

01:52:29.560 | So the goal of any treatment to keep neurons

01:52:32.400 | or other cells youthful and functioning well,

01:52:35.860 | and to prevent or reverse aging is going to be

01:52:39.780 | to increase ATP and to reduce reactive oxygen species.

01:52:44.140 | And in doing so, to disrupt some of the normal pathways

01:52:48.480 | associated with aging.

01:52:51.860 | The Jeffrey lab approached these studies with that

01:52:54.040 | understanding of how mitochondria and reactive oxygen species

01:52:57.160 | and ATP work.

01:52:58.700 | And what they did was exquisitely simple to the point

01:53:02.060 | of being elegant.

01:53:02.900 | And what they found was really, really exciting.

01:53:05.240 | What they did is they had people,

01:53:08.600 | subjects that were either younger,

01:53:10.440 | so in their twenties or 40 years old or older,

01:53:14.000 | view red light of about 670 nanometers.

01:53:18.000 | 670 nanometers would appear red to you and me.

01:53:21.520 | They had them do that, excuse me,

01:53:23.640 | at a distance that was safe for their eyes.

01:53:25.620 | So at about a foot away.

01:53:27.720 | Now, a foot away from a very intense red light

01:53:31.700 | could actually be damaging to the eyes.

01:53:33.020 | So they had them do this at about a foot away

01:53:35.200 | from a red light that was of low enough intensity

01:53:37.960 | that did not damage the eyes.

01:53:39.960 | And they had them do that anywhere from two to three minutes

01:53:42.980 | per day.

01:53:44.120 | And in one study, they had them do that

01:53:45.840 | for a long period of time of about 12 weeks.

01:53:48.360 | And in the other study, they had them do that

01:53:49.760 | just for a couple of weeks.

01:53:51.680 | What's remarkable is that when you collapse the results

01:53:54.560 | across these two studies,

01:53:56.080 | what they found is that when looking at these subjects

01:53:58.660 | ranging from 28 years old to about 72 years old,

01:54:02.880 | the major findings were that in individuals 40 years old

01:54:07.880 | or older, so in the 40 to 72 year old bracket,

01:54:12.920 | but not in the subjects younger than 40 years old,

01:54:16.600 | they saw an improvement in visual function.

01:54:20.120 | That improvement in visual function was an improvement

01:54:22.440 | in visual acuity, meaning the ability to resolve,

01:54:25.440 | find detail, and using a particular measure

01:54:28.840 | of visual function, which is called the Tritan exam,

01:54:33.840 | T-R-I-T-A-N, Tritan exam, which specifically addresses

01:54:39.080 | the function of the so-called short wavelength cones,

01:54:42.360 | the ones that respond to green and blue light.

01:54:45.000 | They saw a 22% improvement in visual acuity,

01:54:48.840 | which in the landscape of visual testing

01:54:52.240 | is an extremely exciting result, okay?

01:54:55.540 | So I think in most studies of improvements of vision,

01:54:59.220 | you'd be very excited to see an improvement of 5% or 10%.

01:55:03.320 | So a 22% improvement in visual acuity,

01:55:06.520 | even though it's in this very specific form

01:55:08.980 | of visual testing, this Tritan exam or this Tritan score,

01:55:13.720 | well, that turns out to be very significant

01:55:16.000 | and translates to the real world in an important way.

01:55:20.200 | In particular, as we age,

01:55:23.080 | we tend to lose certain neurons within our retina,

01:55:26.120 | but we don't tend to lose cones.

01:55:28.520 | We tend to lose rods.

01:55:30.160 | We tend to lose other cells within the retina,

01:55:32.280 | including the cells that connect the eye to the brain,

01:55:34.240 | the so-called ganglion cells.

01:55:35.800 | Cones for whatever reason are pretty resilient

01:55:38.660 | to age-related loss.

01:55:40.200 | However, because rods and cones both

01:55:44.460 | are not just among the most metabolically active cells

01:55:47.720 | in your entire body,

01:55:49.120 | but the most metabolically active cells in your entire body.

01:55:52.960 | That's right, your rods and cones are the cells that demand

01:55:56.200 | and that use the most energy of all the cells in your body.

01:55:59.860 | Not your skin cells, not your spleen cells,

01:56:02.520 | not your stomach cells.

01:56:03.720 | Even if you talk a lot,

01:56:04.920 | not the cells that are responsible for moving your mouth,

01:56:07.120 | it is the rods and cones of your neural retina

01:56:09.680 | that are responsible for using the most amount

01:56:12.680 | of ATP and energy in your entire body.

01:56:15.640 | And because of that, those cells tend to accumulate

01:56:19.080 | a lot of reactive oxygen species as we age.

01:56:22.280 | Red light of the sort used in these studies

01:56:25.360 | was able to reduce the amount of reactive oxygen species

01:56:29.920 | in the rods and cones,

01:56:31.360 | and to rescue the function of this particular cone type,

01:56:35.200 | the short wavelength and medium wavelength cones,

01:56:37.020 | which if you think about the study

01:56:38.480 | is a little bit surprising because it was red light

01:56:41.200 | and near infrared light, not short wavelength light

01:56:44.120 | that was used in order to create this improvement

01:56:47.040 | in cellular function.

01:56:48.560 | But if you step back a little bit further,

01:56:51.000 | it makes perfect sense because there's nothing specific

01:56:54.760 | about the red light in the sense that it's not,

01:56:56.940 | that it gets delivered only to red cones.

01:56:59.600 | That red light and near infrared light is being absorbed

01:57:02.400 | by all the photoreceptors within the eye,

01:57:04.700 | the rods and the blue cones and the green cones

01:57:07.640 | and the red cones.

01:57:08.480 | It's just that the red cones absorb that light best.

01:57:11.760 | So the important takeaway here is that viewing red light

01:57:16.340 | and near infrared light at a distance at which it is safe

01:57:19.780 | for just a couple of minutes each day allowed a reversal

01:57:23.680 | of the aging process of these neurons,

01:57:25.920 | which some people have heard me say before,

01:57:28.640 | and I'll just say it again,

01:57:30.320 | the retina, including your photoreceptors

01:57:32.200 | are not just connected to your brain.

01:57:34.160 | They're not just near your brain.

01:57:35.280 | They are actual central nervous system tissue.

01:57:37.400 | They are the only two pieces of your brain.

01:57:39.560 | Many of your neural retinas are the only two pieces

01:57:41.480 | of your brain that reside outside your skull

01:57:43.320 | or at least outside the cranial vault.

01:57:45.000 | So here we're seeing a reversal of the aging process

01:57:48.280 | in neurons by shining red light on those neurons.

01:57:51.560 | Now, of course, the Jeffrey Lab is primarily interested

01:57:55.160 | in vision and humans are most dependent on vision

01:57:58.040 | as a sense to navigate the world and survive.

01:57:59.880 | So this is really wonderful.

01:58:01.240 | Here we're looking at a therapy

01:58:03.040 | that can reverse age-related vision loss,

01:58:06.560 | at least in some individuals.

01:58:08.680 | But as you can imagine, the study was also done

01:58:10.480 | on these cells because they reside outside the skull

01:58:13.080 | and you can shine light directly on them, right?

01:58:15.320 | I'm sure that there are many people out there

01:58:16.980 | who are interested in how they can improve the function,

01:58:19.440 | say of the neurons in their brain responsible for memory.

01:58:22.600 | And in a few minutes,

01:58:23.440 | I'll describe the non-invasive applications of light

01:58:27.000 | to try and restore the function of those cells as well.

01:58:31.060 | So a little bit more about the studies from the Jeffrey Lab.

01:58:35.900 | One of the things that they observed was a reduction

01:58:38.860 | in so-called drusen, D-R-U-S-E-N.

01:58:41.720 | Drusen are little fatty deposits, little cholesterol deposits

01:58:46.720 | that accumulate in the eye as we age.

01:58:49.880 | We've all heard about cholesterol

01:58:51.540 | within our veins and arteries

01:58:53.080 | and how that can clog our veins and arteries

01:58:55.660 | and how, of course, clogging of veins and arteries

01:58:58.720 | is not a good thing.

01:58:59.760 | Well, our neural retina being so metabolically active

01:59:02.540 | requires a lot of blood flow, it's heavily vascularized.

01:59:06.140 | And drusen are a special form of cholesterol

01:59:09.080 | that accumulate in the eye.

01:59:10.380 | As it turns out, these red light

01:59:12.900 | and near-infrared light therapies

01:59:15.020 | explored by the Jeffrey Lab

01:59:16.480 | were able to actually reduce or reverse

01:59:19.560 | some of the accumulation of drusen.

01:59:21.600 | And so in addition to reducing reactive oxygen species,

01:59:25.620 | the idea in mind now is that red light

01:59:27.980 | may actually reduce cholesterol deposits

01:59:31.520 | and reactive oxygen species

01:59:34.060 | in order to improve neuronal function.

01:59:36.520 | So what should you and I do with these results?

01:59:38.740 | Or should we do anything with these results?

01:59:40.220 | Well, first of all, I want to emphasize

01:59:42.220 | that even though these studies are very exciting,

01:59:44.680 | they are fairly recent.

01:59:45.920 | And so more data, as always, are needed.

01:59:48.960 | There's some additional features of these studies

01:59:50.660 | that I think are also important to consider.

01:59:52.580 | First of all, the exposure to red light

01:59:55.780 | needed to happen early in the day,

01:59:58.380 | at least within the first three hours of waking.

02:00:01.160 | How would one do that?

02:00:03.120 | Well, nowadays there are a number

02:00:04.640 | of different red light panels

02:00:06.600 | and different red light sources

02:00:08.880 | that certainly fall within the range of red light

02:00:11.740 | and near-infrared light that one could use.

02:00:14.260 | I don't have any affiliation to any companies

02:00:17.120 | or products that promote or make those red light therapies.

02:00:21.640 | I do own a red light panel.

02:00:23.380 | So I confess I have started using this protocol.

02:00:25.920 | I am older than 40 years old.

02:00:27.800 | I also have been experimenting with these red light panels

02:00:30.720 | as a way of addressing other changes in biological tissues

02:00:35.500 | for which I'm doing blood work, et cetera.

02:00:37.140 | And I'm going to talk about that in a future episode,

02:00:39.480 | but that of course is what I call anecdotal data.

02:00:41.560 | It only relates to my experience.

02:00:43.180 | So today, and certainly on all episodes

02:00:46.360 | of the Huberman Lab Podcast,

02:00:47.700 | we emphasize peer-reviewed studies almost exclusively

02:00:50.700 | talking about anecdotal data

02:00:52.020 | only when highlighting it as anecdotal data.

02:00:54.820 | So if you're somebody who wants to explore red light therapy,

02:00:58.540 | here's what you need to do.

02:00:59.580 | You need to make sure that that red light source,

02:01:02.100 | whatever source you happen to use,

02:01:04.160 | whether or not you purchase it or make one.

02:01:05.500 | And in fact, these red light sources

02:01:07.260 | are very, very easy to make.

02:01:08.860 | You could essentially take a bright flashlight

02:01:11.580 | and cover it with a film or a filter

02:01:14.100 | that would only allow particular long wavelengths

02:01:17.380 | to pass through.

02:01:18.220 | This would be very easy to look up online

02:01:19.860 | and figure out how to do this.

02:01:20.700 | You could probably do this for just a few dollars,

02:01:23.520 | or you could purchase a red light unit

02:01:25.480 | if that was within your budget

02:01:27.440 | and something that you're interested in.

02:01:28.960 | You want to make sure that it's not so bright

02:01:30.800 | that you're damaging your eye.

02:01:32.580 | A good rule of thumb is that something

02:01:34.300 | isn't painful to look at.

02:01:35.880 | And in fact, I should just emphasize

02:01:37.360 | that anytime you look at any light source,

02:01:39.520 | sunlight or otherwise that's painful

02:01:41.460 | and makes you want to squint or close your eyes,

02:01:43.000 | that means it's too bright to look at

02:01:44.860 | without closing your eyes.

02:01:45.980 | Okay, that's sort of a duh,

02:01:47.380 | but I would loathe to think that anyone

02:01:49.480 | would harm themselves with bright light in any way.

02:01:51.720 | I don't just say that to protect us.

02:01:52.940 | I say that to protect you, of course,

02:01:54.840 | because you are responsible for your health.

02:01:56.700 | And again, retinal neurons do not regenerate.

02:01:59.260 | Once they are gone and dead, they do not come back.

02:02:02.140 | There's no technology to replace them

02:02:03.740 | at this current state in time.

02:02:06.240 | So please don't damage your retinas.

02:02:08.360 | So is a red light source safe to look at

02:02:10.820 | if it is not painful to look at?

02:02:13.460 | Chances are it is, and yet I would still encourage you

02:02:16.000 | to talk to your optometrist or ophthalmologist

02:02:19.180 | before getting into any extensive protocols.

02:02:21.900 | But if you were still determined to pursue

02:02:24.060 | the sorts of protocols that are in the Jeffrey studies,

02:02:26.260 | certainly we'll provide a link to those studies.

02:02:28.400 | Again, it involves looking at these red light panels,

02:02:31.140 | blinking aloud for two minutes to three minutes,

02:02:36.140 | every morning for a period of two weeks or more.

02:02:40.760 | And if you're older than 40,

02:02:44.820 | that could very well have an effect.

02:02:46.200 | If you're longer, younger than 40, excuse me,

02:02:48.540 | that's unlikely to have an effect.

02:02:50.700 | At least that was what was observed

02:02:52.460 | in these particular studies.

02:02:54.060 | The lights were not flashing.

02:02:55.540 | It was continuous illumination.

02:02:57.220 | Again, you're allowed to blink.

02:02:58.820 | It does not have to even be direct illumination.

02:03:00.820 | It can be somewhat indirect illumination,

02:03:02.460 | much as we described for the use of UVB light before.

02:03:06.220 | The wavelength of light is important.

02:03:08.180 | It is red light and near-infrared light

02:03:10.180 | that is going to be effective in this scenario.

02:03:14.020 | The authors of this study emphasize that it was red light

02:03:16.780 | of 670 nanometers in wavelength

02:03:20.220 | and near-infrared light of 790 nanometers in wavelength.

02:03:25.780 | That were effective.

02:03:26.820 | And that those wavelengths could be complimentary.

02:03:29.720 | That's probably why, or maybe it's just coincidental,

02:03:33.200 | but it's a fortunate coincidence

02:03:35.220 | that a lot of the commercially available red light panels

02:03:37.680 | that you'll find out there

02:03:38.520 | combine both red light and near-infrared light.

02:03:41.500 | However, I want to emphasize that most of the panels

02:03:44.280 | that are commercially available are going to be too bright

02:03:47.940 | to safely look at very close up.

02:03:50.500 | And in fact, that's why most of those red light panels

02:03:53.020 | are designed for illumination of the skin

02:03:54.980 | and oftentimes arrive in their packaging with eye protectors

02:03:58.940 | that are actually designed to shield out all the red light.

02:04:01.740 | So take the potential dangers of excessive illumination

02:04:06.220 | of the eyes with any wavelength of light seriously.

02:04:09.260 | But if you're going to explore 670 and 790 nanometer light

02:04:12.820 | for sake of enhancing neuronal function,

02:04:16.340 | set it at a distance that's comfortable to look at

02:04:18.660 | and that doesn't force you to squint

02:04:20.340 | or doesn't make you feel uncomfortable physically

02:04:22.940 | as if you need to turn away during the period

02:04:26.280 | of that two to three minute illumination each day.

02:04:28.780 | In terms of turning away from light,

02:04:32.380 | I'll just briefly mention that that is not an accident

02:04:36.020 | or a coincidence that you have that response

02:04:37.780 | to very bright light.

02:04:38.980 | There is a so-called photic avoidance pathway

02:04:41.820 | that involves cells within your retina,

02:04:43.660 | these ganglion cells that communicate

02:04:45.260 | with yet another brain station,

02:04:48.120 | a certain area of your thalamus

02:04:49.900 | that communicate to areas of your brain

02:04:52.400 | that are associated with pain.

02:04:53.580 | So literally that can trigger headache

02:04:55.340 | and that can trigger the squint reflex.

02:04:57.460 | Biology is just beautiful in this way.

02:05:00.420 | Too much light is bad for us in that it can damage our eyes

02:05:03.480 | and other aspects of our body.

02:05:05.160 | So if we look at a light that's too bright,

02:05:07.380 | our eyes send a signal to the brain

02:05:08.980 | that gives us a sort of a headache

02:05:10.360 | and a desire to squint and turn away.

02:05:12.100 | So that can be a useful guide

02:05:14.040 | in terms of gauging how bright a light should be

02:05:16.680 | or at least how far away you should be from a bright source

02:05:19.980 | in order to safely engage with that light source.

02:05:23.080 | So the studies I just described, once again,

02:05:25.880 | involve the use of red light early in the day

02:05:27.980 | within three hours of waking

02:05:29.400 | and are for the sake of improving neuronal function.

02:05:31.760 | Red light has also been shown to be beneficial

02:05:35.760 | late in the day and even in the middle of the night.

02:05:38.160 | And when I say middle of the night,

02:05:40.260 | I'm referring to studies that explore the use of red light

02:05:43.100 | for shift workers.

02:05:44.620 | I know that most people are not working

02:05:46.380 | in the middle of the night, at least I hope they're not,

02:05:48.040 | but some of you may do that from time to time.

02:05:50.440 | All-nighters for studying, I confess,

02:05:51.920 | I still pull all-nighters every once in a while

02:05:53.580 | to prepare things like podcasts and other deadlines.

02:05:57.160 | Really try not to, happens less and less as I get older

02:05:59.760 | because I think I get more disciplined

02:06:01.640 | and or less good at pulling all-nighters.

02:06:04.960 | But I realized that many people are doing shift work

02:06:07.360 | or they have to work certainly past 10 p.m.

02:06:09.760 | or maybe they're taking care of young children

02:06:11.600 | in the middle of the night and they have to be up.

02:06:14.040 | In that case, red light can actually be very beneficial.

02:06:16.400 | And nowadays there are a lot of sources of red light

02:06:19.000 | available just as red light bulbs, you don't need a panel.

02:06:21.940 | So what I'm basically saying is that it can be beneficial

02:06:25.220 | to use red lights at night.

02:06:28.080 | The study I'd like to emphasize in this context

02:06:30.160 | is entitled Red Light,

02:06:31.880 | a Novel Non-Pharmacological Intervention

02:06:34.160 | to Promote Alertness in Shift Workers.

02:06:36.800 | So beautiful study.

02:06:38.000 | They explored the use of different wavelengths of light.

02:06:41.360 | So blue light of 460 nanometers or red light

02:06:45.260 | or dim white light of different brightnesses, et cetera,

02:06:49.500 | and looked at things like melatonin.

02:06:52.720 | How much does light of a given color

02:06:55.160 | and intensity suppress melatonin?

02:06:56.800 | They looked at cortisol, a stress hormone.

02:06:58.580 | They looked at wakefulness.

02:07:00.320 | How much or to what degree could a given color of light

02:07:03.600 | increase wakefulness at different hours of the day?

02:07:06.220 | The takeaway from this study is very clear.

02:07:08.320 | If you need to be awake late at night

02:07:10.540 | for sake of shift work or studying

02:07:12.320 | or taking care of children, et cetera,

02:07:14.780 | red light is going to be your best choice

02:07:17.500 | because if the red light is sufficiently dim,

02:07:21.240 | it's not going to inhibit melatonin production

02:07:25.000 | and it's not going to increase cortisol at night.

02:07:28.080 | Cortisol should be high early in the day

02:07:30.800 | or at least should be elevated

02:07:31.960 | relative to other times of day if you are healthy.

02:07:34.500 | A late shifted increase in cortisol, however,

02:07:36.840 | 9 p.m. cortisol, 10 p.m. cortisol

02:07:39.020 | is well known to be associated with depression

02:07:42.120 | and other aspects of mental health

02:07:44.480 | which is a mental illness.

02:07:46.380 | So if you do need to be awake at night or even all night,

02:07:50.100 | red light is going to be the preferred light source.

02:07:53.620 | And in terms of how bright to make it,

02:07:55.380 | well, as dim as you can while still being able

02:07:59.000 | to perform the activities that you need to perform,

02:08:00.840 | that's going to be your best guide.

02:08:03.060 | I'll provide a link to this study as well.

02:08:05.420 | Again, it's a really important study

02:08:08.100 | because it emphasized that there are forms of light,

02:08:10.320 | red light provided it's dim,

02:08:12.240 | that can allow you to stimulate the alertness

02:08:15.400 | that light landing on the eyes can provide.

02:08:19.080 | So it allows you to stay awake

02:08:20.200 | and to do whatever work that you need to do.

02:08:22.520 | It does not seem to alter melatonin production.

02:08:26.040 | So that's good.

02:08:26.860 | It does not seem to alter levels

02:08:28.880 | or timing of cortisol production.

02:08:31.000 | So yet another case where red light used correctly

02:08:34.680 | can be beneficial.

02:08:35.800 | Up until now, we've been talking about the effects

02:08:37.760 | of shining different wavelengths of light on the skin

02:08:41.440 | or on our eyes and the downstream health consequences

02:08:45.640 | of that illumination.

02:08:47.560 | However, one of the most important goals

02:08:49.560 | of science and medicine is to figure out

02:08:52.000 | how to change the health of our brain.

02:08:54.600 | And of course our brain is contained within our skull

02:08:58.240 | and therefore we can't just shine light

02:09:01.160 | onto the outside of our head

02:09:03.440 | and expect it to change the activity of neurons

02:09:06.000 | deep within the brain,

02:09:07.000 | unless those neurons are linked up with our eyes

02:09:11.560 | or with our skin.

02:09:12.580 | And as it turns out,

02:09:13.520 | even though there are a lot of brain areas

02:09:15.480 | that are connected through neural circuits

02:09:17.680 | and hormone circuits through our eye

02:09:19.580 | and believe it or not also to our skin,

02:09:22.240 | many brain areas are not.

02:09:24.140 | Brain areas such as the hippocampus,

02:09:27.800 | which is involved in learning and memory,

02:09:30.220 | brain areas such as our neocortex.

02:09:33.180 | Well, some areas of our neocortex,

02:09:34.840 | such as our visual cortex are indirectly linked to our eyes.

02:09:38.400 | So if we shine light on our eyes,

02:09:39.600 | we can change the activity of neurons in our neocortex,

02:09:42.420 | but there are other brain areas that are not directly

02:09:46.520 | or even indirectly connected to our visual system,

02:09:50.060 | not at least in any immediate way.

02:09:53.080 | So that raises the question of how do you change

02:09:55.040 | the activity of neurons in the brain?

02:09:56.400 | Well, there's pharmacology.

02:09:58.080 | You can take pills,

02:09:59.800 | you can inject drugs that will change the pharmacology

02:10:02.360 | of neurons and the way they operate in fire.

02:10:04.840 | Of course, antidepressants are one such instance.

02:10:07.760 | Opioid drugs are another.

02:10:09.720 | There's a huge array of psychoactive compounds,

02:10:12.700 | meaning compounds that will change the levels

02:10:14.700 | of chemicals in your brain.

02:10:16.760 | Some of those work.

02:10:17.640 | Many of them also carry side effects.

02:10:20.700 | It's all rather indirect,

02:10:22.540 | meaning you have lots of different cells

02:10:24.320 | in different areas of your brain

02:10:25.300 | that utilize the same chemicals.

02:10:26.640 | So a drug, for instance, to increase serotonin

02:10:29.060 | for sake of improving depression

02:10:31.520 | will also often have the effect

02:10:33.560 | of reducing certain neurons output of serotonin

02:10:38.080 | in the hippocampus and cause changes in appetite

02:10:40.280 | or changes in libido and so on and so forth.

02:10:42.480 | You could imagine using electrical stimulation,

02:10:45.260 | putting wires into the brain

02:10:46.420 | and stimulating specific brain areas

02:10:48.520 | in order to activate the neurons in those brain areas.

02:10:51.320 | And certainly that works and has been done experimentally

02:10:53.960 | and is done during neurosurgery exams, et cetera,

02:10:56.860 | but involves removing a piece of skull.

02:10:59.600 | So that's not very practical.

02:11:01.320 | In principle, light would be a wonderful way

02:11:04.360 | to modulate the activity of neurons deep within the brain.

02:11:08.460 | But again, the skull is in the way.

02:11:10.320 | Recent studies, however, have figured out ways

02:11:14.400 | that light can be delivered to the eyes

02:11:16.720 | to change global patterns of firing in the brain

02:11:20.220 | in ways that can be beneficial to the brain.

02:11:22.640 | And the work that I'm referring to now

02:11:25.480 | is mainly the work of Liwei Tsai at MIT,

02:11:28.560 | Massachusetts Institute of Technology and her colleagues.

02:11:32.120 | And what they've discovered is that there's a particular

02:11:34.840 | pattern of brain activity called gamma activity.

02:11:38.940 | Gamma activity is one so-called wavelength

02:11:42.080 | of electrical activity in the brain.

02:11:44.200 | So not wavelengths of light,

02:11:45.220 | but wavelengths of electrical activity in the brain

02:11:47.980 | that can be restorative for certain aspects

02:11:50.520 | of learning and memory and can actually help create

02:11:53.080 | molecular changes in neurons that lead to clearance

02:11:56.780 | of debris and even reductions

02:11:59.240 | in age-related cognitive decline.

02:12:01.760 | So the way to think about brain waves and brain oscillations

02:12:06.760 | is that neurons are electrically active,

02:12:09.280 | that involves chemicals, et cetera.

02:12:11.120 | And they can be active in very slow, big wave forms.

02:12:15.200 | So you can think of, you know, delta waves,

02:12:17.840 | meaning, so you can imagine a wave of electrical activity

02:12:20.400 | that comes along very infrequently.

02:12:22.200 | So a given neuron fires and then some period of time later

02:12:26.120 | fires and then some period of time even later fires.

02:12:29.680 | Or you can imagine that that same cell is very active,

02:12:32.520 | fires, fires, fires, fires, fires.

02:12:34.340 | You can imagine if it's firing very often,

02:12:36.000 | it's going to be short wavelength, right?

02:12:38.400 | Shorter gaps between firing,

02:12:40.340 | or if it's firing very seldom,

02:12:43.560 | you're going to think about that

02:12:45.480 | as longer wavelength firing.

02:12:47.280 | Turns out that gamma waves are one pattern of firing

02:12:51.020 | that lead to downstream metabolic functions

02:12:54.760 | and biological functions that end up clearing away debris

02:12:57.340 | that's associated with aging in cells.

02:13:00.200 | And that also lead to molecular changes

02:13:03.280 | that enhance the kind of youthfulness of neurons,

02:13:06.400 | so to speak.

02:13:07.240 | How do we induce gamma oscillations within the brain?

02:13:12.400 | Well, what Liwei, Tsai and colleagues have beautifully shown

02:13:17.220 | is that by delivering certain patterns of light flicker,

02:13:22.040 | so lights going on and off at a particular frequency,

02:13:25.320 | the brain as a whole starts to entrain,

02:13:28.480 | meaning it matches to those particular patterns

02:13:30.860 | of light flicker,

02:13:31.700 | even though many of the brain areas that do this

02:13:34.360 | are not directly within the visual system or visual pathway.

02:13:38.680 | So the studies that I'm referred to are several,

02:13:42.040 | but the one that I'd like to highlight is entitled

02:13:43.920 | Gamma Entrainment Binds Higher Order Brain Regions

02:13:46.780 | and Offers Neuroprotection.

02:13:49.140 | What they essentially did was to expose subjects to 40 Hertz,

02:13:54.140 | which is a particular frequency of illumination to the eyes.

02:13:59.140 | So it's light goes on, light goes off, light goes on,

02:14:02.020 | light goes off at a frequency of 40 Hertz.

02:14:06.220 | And when they did that,

02:14:07.620 | and they recorded the activity of neurons within the brain,

02:14:10.360 | not just within the visual areas of the brain,

02:14:12.920 | but within other areas as well,

02:14:14.840 | they observed increased gamma oscillations,

02:14:18.820 | meaning that the electrical activity of the brain at large

02:14:23.040 | started to match to the patterns of light

02:14:26.080 | that were delivered to the eyes.

02:14:27.980 | This is really exciting and very unique

02:14:29.720 | from the different types of phototherapies

02:14:31.620 | that we've been talking about up until now.

02:14:33.200 | All the patterns of phototherapy

02:14:35.080 | that we've been talking about up until now

02:14:36.680 | involved constant illumination with a given wavelength.

02:14:39.280 | Here it is wavelength generating patterns of illumination,

02:14:44.280 | light on, light off, light on, light off

02:14:46.600 | at a particular frequency.

02:14:48.480 | So what they found, for instance,

02:14:49.740 | using this pattern of stimulation,

02:14:51.200 | and by the way, the stimulation was called GENUS,

02:14:53.640 | gamma entrainment using sensory stimulation.

02:14:56.160 | So G-E-N-U-S, gamma entrainment using sensory stimulation,

02:15:00.000 | had a number of really interesting effects.

02:15:01.560 | First of all, it reduced so-called amyloid plaques

02:15:04.920 | and phosphorylated tau.

02:15:06.680 | Amyloid plaques and phosphorylated tau

02:15:08.360 | are associated with Alzheimer's

02:15:09.760 | and normal age-related cognitive decline.

02:15:12.840 | So this is incredible, right?

02:15:15.920 | A pattern of flashing light delivered to the eyes

02:15:19.240 | creates a pattern of neuronal firing,

02:15:21.360 | not just in the visual areas of the brain,

02:15:23.120 | but in other areas of the brain as well,

02:15:25.600 | that in turn trigger molecular pathways

02:15:28.720 | that reduce some of the markers

02:15:32.000 | and the cause of age-related cognitive decline

02:15:34.460 | in Alzheimer's.

02:15:35.520 | And in parallel to that,

02:15:37.200 | they observed an upregulation

02:15:39.120 | of some of the biological pathways

02:15:41.300 | that lead to enhancement of neuronal function,

02:15:43.500 | maintenance of synapses,

02:15:44.620 | which are the connections between neurons

02:15:46.480 | and so on and so on.

02:15:48.320 | They have discovered and list out a huge number

02:15:50.820 | of these biological effects,

02:15:52.400 | both the reduction in bad things, so to speak,

02:15:55.280 | and the improvement in good biological pathways.

02:15:59.080 | And I find these studies so exciting

02:16:02.060 | because first of all, they're non-invasive, right?

02:16:05.560 | There's no drilling through the skull.

02:16:07.520 | They are very tractable in the experimental sense,

02:16:11.760 | meaning that you could imagine

02:16:14.020 | that if 40 hertz stimulation turns out

02:16:15.920 | to be the very best stimulation protocol

02:16:17.820 | to induce these gamma oscillations, well, great,

02:16:20.360 | but because it's non-invasive,

02:16:22.280 | it's fairly easy to explore 50 hertz stimulation,

02:16:25.080 | 100 hertz stimulation, 20 hertz stimulation,

02:16:27.480 | and to do that with different wavelengths of light.

02:16:30.540 | And so that's what's happening now.

02:16:31.780 | The PSI lab and other labs are really starting

02:16:33.600 | to explore the full range of variables

02:16:36.680 | that can impact oscillations within the brain

02:16:39.680 | and their downstream consequences.

02:16:41.440 | So again, this is phototherapy,

02:16:43.600 | but phototherapy of a very different sort

02:16:45.400 | that we've been talking about up until now.

02:16:47.840 | It's phototherapy designed to trigger activation

02:16:50.920 | of biological pathways far away

02:16:53.360 | from the very tissue that's being illuminated.

02:16:55.240 | And it calls to mind the same sorts of mechanisms

02:16:57.300 | that we were talking about earlier,

02:16:58.320 | where illumination of the skin with UVB light

02:17:00.840 | is setting off an enormous number of different cascades

02:17:03.120 | in different organs and tissues, including the spleen,

02:17:05.680 | the testes, the ovaries, and so on.

02:17:08.140 | So again, light has these powerful effects,

02:17:11.760 | both locally on the cells that the light is delivered to,

02:17:15.060 | but also systemically in terms of the cells

02:17:18.440 | that are changing their electrical and chemical outputs

02:17:21.680 | are modifying lots and lots of biological programs.

02:17:24.720 | Is there an actionable tool related to these studies yet?

02:17:27.920 | Well, that sort of depends on how adventurous you are.

02:17:30.280 | Right now, these studies are being explored

02:17:32.880 | in the context of clinical trials

02:17:34.500 | in people with Alzheimer's dementia

02:17:36.320 | and other forms of neuronal degeneration.

02:17:39.360 | Is it dangerous to look at?

02:17:41.720 | A 40 Hertz flickering light?

02:17:44.080 | Well, in general, the answer is going to be no.

02:17:46.820 | However, if you're prone to epilepsy, for instance,

02:17:49.960 | staring at a flickering light

02:17:51.240 | of a given continuous frequency can induce seizure, right?

02:17:55.180 | That might surprise some of you, but it shouldn't,

02:17:57.680 | because as this study illustrates,

02:18:00.040 | and as anyone who's ever been out at night to a club

02:18:03.100 | or something illustrates,

02:18:04.520 | when you look at a strobe light, for instance,

02:18:07.800 | your whole world of visual perception changes,

02:18:09.920 | but actually the rhythm at which you perceive music,

02:18:13.200 | at which you perceive conversation,

02:18:14.440 | at which you perceive the movement of your body

02:18:16.200 | actually changes according to the patterns of visual flicker

02:18:19.720 | in most cases, strobe,

02:18:21.160 | if we're using the sort of club dancing example,

02:18:24.800 | your brain is in training to its outside environment.

02:18:28.080 | So given the power of flickering lights

02:18:30.840 | to entrain brain rhythms, I think at this stage,

02:18:34.400 | it's probably too preliminary

02:18:36.500 | to really suggest a specific protocol,

02:18:38.760 | but I would definitely keep an eye out

02:18:41.400 | for these sorts of studies.

02:18:43.700 | They are coming out all the time.

02:18:45.280 | And I think in a very short period,

02:18:47.920 | we're going to see specific protocols

02:18:50.420 | that one could potentially use even at home.

02:18:53.020 | And of course, these are non-invasive protocols

02:18:54.920 | in order to place the brain into a particular state,

02:18:58.700 | not just for sake of offsetting neurodegeneration,

02:19:01.540 | but also for enhancing focus,

02:19:03.880 | for enhancing the transition into sleep

02:19:05.920 | and other brain states as well.

02:19:07.620 | Today, I covered what I would say is a lot of information.

02:19:11.240 | My goal was to give you an understanding

02:19:13.000 | of how light can be used to change the activities of cells,

02:19:17.780 | organelles within those cells, entire organs,

02:19:21.420 | and how that can happen locally and systemically.

02:19:25.900 | We talked about the power of light to impact our biology

02:19:28.520 | at the endocrine level, neuronal level,

02:19:30.360 | immune level, mood, et cetera,

02:19:33.460 | through both illumination of the eyes and the skin

02:19:36.640 | and other tissues as well.

02:19:38.700 | I realized that even though this was a lot of information,

02:19:42.360 | there are many aspects of phototherapy that I did not cover.

02:19:46.380 | I know there's a lot of interest nowadays, for instance,

02:19:48.520 | in the use of red light and other wavelength light therapies

02:19:52.160 | for ovarian health and testicular health.

02:19:55.420 | In fact, I get a lot of questions such as,

02:19:59.120 | can red light be used to improve testosterone output?

02:20:02.200 | And if so, is that best accomplished

02:20:04.420 | by shining red light on the skin

02:20:06.720 | or directly on the gonads, on the testicles?

02:20:09.500 | I'm going to cover those data at a future time.

02:20:13.460 | Right now, the studies that have been done in rodents,

02:20:16.220 | I don't think are easily enough translated to humans.

02:20:19.140 | And the studies that are happening in humans now

02:20:21.460 | are exciting in the sense that they hold a lot of potential,

02:20:24.520 | but the data aren't clear yet.

02:20:27.540 | However, the data using UVB on the skin of men and women

02:20:32.980 | in order to increase hormone,

02:20:35.240 | in particular testosterone and estrogen output,

02:20:37.220 | those data I think are very exciting and very actionable.

02:20:40.220 | And we talked about those earlier.

02:20:41.980 | So if you want more information

02:20:43.860 | on how phototherapy can be used,

02:20:45.600 | certainly we will do another episode on phototherapy

02:20:48.780 | in these other contexts.

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02:22:58.300 | I'm also pleased to announce

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02:23:23.500 | at Hubermanlab.com/tour.

02:23:26.360 | So thank you once again for joining me today

02:23:28.440 | for this deep dive discussion into phototherapies,

02:23:31.640 | meaning the power of light

02:23:32.820 | to modulate our biology and health.

02:23:34.860 | And as always, thank you for your interest in science.

02:23:37.960 | (upbeat music)

02:23:40.540 | (upbeat music)

Using Light (Sunlight, Blue Light & Red Light) to Optimize Health | Huberman Lab Podcast #68

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