- Welcome to the Huberman Lab Podcast, where we discuss science and science-based tools for everyday life. I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. Today, we are discussing colds and flus. We will talk about what a cold really is and what a flu really is in terms of how they impact your brain and body.

And of course, we will discuss how to avoid getting colds and flus. There are indeed some excellent science-supported techniques to avoid getting colds and flus, but of course, it is impossible to completely avoid ever getting a cold or flu in your lifetime. So we also discuss how to more quickly get over a cold or flu should you happen to catch one.

So during today's discussion, I'll talk about the immune system. I'll give you some mechanistic understanding of how your immune system works, and I promise to make that discussion accessible to everybody, regardless of whether or not you have a background in biology. And with that understanding of how your immune system works, you will be in a much better position to understand which tools, that is which protocols to implement, should you be exposed to a cold or flu, or if you are trying to get over a cold or flu more quickly than you would otherwise.

You'll learn about some potent behavioral tools for bolstering your immune system. And we will also discuss various compounds that you might consider taking to enhance the function of your immune system to ward off or treat colds and flus. I will also be dispelling a number of common myths about treatments for the common cold and for the flu.

There are oh so many ideas out there about what one could take or do in order to avoid getting the cold or flu or more quickly get relief from a cold or flu. However, many of those are pure myth. There's just no science to support them. And indeed there's some science that counters those ideas.

But the good news is there are indeed science supported behavioral protocols and compounds that one could consider in order to avoid and treat colds and flus. Before we begin, I'd like to emphasize that this podcast is separate from my teaching and research roles at Stanford. It is however, part of my desire and effort to bring zero cost to consumer information about science and science related tools to the general public.

In keeping with that theme, I'd like to thank the sponsors of today's podcast. Our first sponsor is Juve. Juve makes medical grade red light therapy devices. Now, if there's one thing I've consistently emphasized on this podcast is the incredible role that light can have on our biology. And of course, I'm always telling people that they should get sunlight in their eyes as soon as possible after waking on as many days of their life as possible for sake of setting circadian rhythm, daytime mood focus and alertness and improve sleep.

Now, in addition to sunlight, red light and near infrared light has been shown to have positive effects on improving numerous aspects of cellular and organ health, including faster muscle recovery, improved skin health and wound healing, even improvements in acne, or that is removal of acne, reducing pain and inflammation, improving mitochondrial function and even improving vision itself.

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And I also own a Juve panel that allows for full body exposure. And I use that one approximately five times per week for about 10 to 15 minutes per session. If you'd like to try Juve, you can go to Juve, spelled J-O-O-V-V.com/huberman. Again, that's juve.com/huberman. For this month only, January, 2024, Juve is offering exclusive discounts to Huberman Lab listeners with up to $500 off select Juve products.

Again, that's juve, spelled J-O-O-V-V.com/huberman to get up to $500 off select Juve products. Today's episode is also brought to us by Helix Sleep. Helix Sleep makes mattresses and pillows that are tailored to your unique sleep needs. Now, sleep is the foundation of mental health, physical health, and performance. When we are sleeping well and enough, mental health, physical health, and performance all stand to be at their best.

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Again, if interested, go to helixsleep.com/huberman for up to $350 off and two free pillows. Today's episode is also brought to us by Roka. Roka makes eyeglasses and sunglasses that are the absolute highest quality. I've spent a lifetime working on the biology of the visual system. I can tell you that your visual system has to contend with an enormous number of challenges in order for you to be able to see clearly.

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Again, that's R-O-K-A.com and enter the code Huberman at checkout. Okay, let's talk about the common cold. First off, no, unfortunately today, I cannot tell you the cure for the common cold because indeed there isn't one. One interesting question, however, is why don't we have a cure for the common cold?

And the reason is that the cold virus, as it's referred to, is actually a bunch of different viruses. Some colds are caused by one, what's called serotype of the virus. Other colds are caused by a different serotype of the virus. There are over 160 different types of what people call the cold virus.

Now, cold viruses fall under an umbrella of a general category of viruses called rhinoviruses. You can remember that easily because rhino sounds like rhino's horn, the rhinoceros horn, which is of course in the center of the rhino's face, which is where your nose is. And the cold almost always causes some degree of nasal symptoms in humans.

It's either runny nose or sneezing or stuffed up nose, or sometimes unfortunately all three. Now, the reason we don't have a cure for the common cold is that all of those different serotypes of the cold virus mean that the virus itself has a different shape on its outside. And as a consequence, even if you've been exposed to a cold and you've developed antibodies against that cold virus, the next cold that comes along very likely has a different shape, and therefore your body's antibodies to the cold virus it combated successfully before can't latch onto and defeat that next different serotype of the cold virus.

Now, a little bit later, I'll talk about the immune system and how those different antibodies are generated. But for the time being, understanding that there are a lot of different types of cold viruses explains, first of all, why we don't have a cure for the common cold, but also why you can get multiple colds within a given year or even within a given season.

Because even if you develop antibodies against one serotype of the cold virus, a different serotype can come along and you can get sick again with that new serotype of the cold virus. So how do you catch a cold? Now, one of the problems with the cold virus being called the cold virus, and the fact that indeed there are more cold viruses present and transmitted between humans in the cold winter months of the year, is that people generally assume that it is the cold temperatures outside that actually give you a cold virus.

And that is simply not true. However, what you heard as a kid, if your mom most likely, but maybe your dad said, "Hey, don't go outside without a sweater or jacket on, you're going to catch a cold, or you're going to catch cold," has propagated this myth that the cold temperatures themselves are the cause of catching a cold virus.

And that's simply not true. The virus that we call the cold virus is spread by breathing, or by sneezing, or by people sneezing or coughing or breathing onto their hands, and then touching surfaces, and then other people touching those surfaces, and then touching most likely their eyes in order to self-infect.

Now, we're going to get into the details of how far the virus can spread with a sneeze, how long it can survive on the hands, et cetera. But for the time being, know this, the cold virus is a pretty stable virus in that it can survive on surfaces, non-human or human surfaces, meaning skin or on a table or on a glass or on a door handle for up to 24 hours.

So for all you hypochondriacs out there, I probably just gave you a little spike in cortisol. And for you non-hypochondriacs, I hope what I just said cues you to the fact that just avoiding people who are sneezing and coughing is not sufficient to avoid getting colds and flus. However, the fact that a cold virus is alive and well on a given surface, let's say on a door handle, does not mean that if you touch that door handle that you will necessarily be infected with that cold virus.

And that's because your skin actually provides an excellent barrier against most viruses and bacteria. Your skin also includes a lot of antiviral substances on it. Even if you haven't put any of that, you know, alcohol stuff or the hand sanitizer stuff on, your skin is a very important barrier component of your immune system.

We're gonna talk about that a little bit later. But if somebody has a cold and they happen to perhaps, you know, wipe their nose or sneeze into a tissue, hopefully into a tissue, and then discard that tissue, the cold virus particles are extremely small. How small? Well, most of us are familiar with thinking about centimeters or inches.

If you think about a millimeter being one one hundredth of a centimeter, well, you can take a millimeter and you can divide that up into a bunch of little slices also, such that you get the micron. The micron is one one thousandth of a centimeter. And if you wanna get a sense of how thick or thin that is, the side of a credit card, the little thin side of a credit card, is about 200 microns thick.

So if you set your credit card flat on a table and then you look at it from the side, that tiny, tiny, thin little edge, that's about 200 microns. The cold virus is made up of particles that are probably in the range of about five microns or so. So it's extremely small.

I mean, the cold virus, therefore, with a good sneeze or even a light sneeze, can spread really far. Now, the good news is those particles are relatively heavy. They don't tend to mist about in the air for very long. They tend to fall down onto the ground or onto surfaces.

But as I mentioned before, they can survive for a very long time on those surfaces. So should you touch your hand to a door handle or table or shake the hand of somebody that has cold virus on their hands, either because they themselves have a cold or they contacted somebody else that had cold virus and it somehow landed on their hands just 'cause the other person sneezed.

All these scenarios are very realistic. That cold virus will not infect you unless it can get inside of your body. And one of the primary entry points of it getting inside your body is via the eyes, by wiping that cold virus on your eyes. Now you may think, okay, I'm just not gonna touch my eyes.

But a little bit later, we're going to talk about a study that shows that almost always, indeed, almost always, when you meet somebody new, you touch your eyes. And the frequency of people touching their face, that is the region of the face around the eyes and their eyes throughout the day is extremely high.

So this is one of the primary routes by which the cold virus is transmitted from one person to the next. But of course, there's also the route that we're all familiar with, which is the person that is sneezing or coughing or blowing their nose into tissues and then throwing them in the trash and not washing their hands after each and every time they do that.

So an important aspect of today's discussion that we will get into once I also present to you what a flu is and how it differs from the cold, is that we're going to need to talk about what stage of infection people are actually contagious with the cold or flu.

And there's actually a lot of mythology about this. In fact, there's a lot of just lying about this. People will be coughing or sneezing and they'll say, oh yeah, I'm not contagious any longer. Or people make up these things like, oh, you know, if you had the flu for two days, then you're no longer contagious.

Or that you can't be contagious until you have symptoms. So we're going to go through all the aspects of contagion and how coughing or sneezing or how long you've had a cold or flu actually relates to whether or not you're contagious in a little bit. But for the time being, know that the cold virus is very, very small.

It can be transmitted through the air. It can be transmitted via contact, from skin to skin contact, and it can survive on surfaces for up to 24 hours. And when you touch those surfaces or a person with the cold virus, most often the way it's going to get into your body and infect you such that you get a cold is by touching your eye region.

Although touching other regions of your body can also pass the cold virus into you. For instance, the mouth and lips, but that's actually far less common. So we'll get into that in just a little bit. Now, different serotypes, that is different types of cold virus, tend to create a different array of overall symptoms such that, you know, one cold might be a really, quote unquote, bad cold.

Others are more mild. Some tend to induce more runny nose, others more stuffy head and a little bit of fever, or in some cases, a lot of fever. One thing that's important to understand is that if people are going to be infected by the cold virus, they tend to develop symptoms one to two days after they were exposed to the virus.

Now, the good news is, if you are exposed to the cold virus, that doesn't necessarily mean that you are going to catch that cold virus. That is, if your immune system can fight off that cold, even if you've never been exposed to that serotype before, then you won't actually have that cold and you won't transmit it.

So put differently, it is possible to avoid getting a cold virus even if you've never been exposed to that serotype of cold virus, and you happen to come into contact with somebody who has that serotype of cold virus, or you touch a surface of some object or handle, et cetera, that has a particular serotype of the cold virus on it, and God forbid, you then wipe your eyes.

That doesn't necessarily mean that you're going to get sick. And a good portion of today's episode is going to focus on tools that are supported by science that allow you to bolster your immune system and greatly increase the probability that even if you're exposed to a novel serotype of the cold virus, that is one that's new to you, that your body's never seen before, that you won't get sick.

Another thing to understand about the cold virus is that you're generally most contagious to other people when you feel at your worst. That is when you're coughing and sneezing and you've got the stuffy head, watery eyes, and so on. But you can also be contagious to other people when you are starting to feel better.

That said, most of the data point to the fact that about five to six days after you hit your peak of worst symptoms, or I guess we should say your nadir, the dip of worst symptoms, 'cause it's such an awful state to be in, you are probably exiting the phase in which you're contagious.

Now, I want to be very clear, that does not mean that if you've had a cold for five or six days, that you are no longer contagious. If you continue to experience sneezing and coughing, watery eyes, in the evening, you're feeling much worse, first thing in the morning, you're feeling especially groggy, et cetera, well, then you are still contagious.

Another way to frame this is, you know those people that continue to show up at the gym and show up at work, and they tell you, "Yeah, I got this cold, "but I've had it for a few days, I'm no longer contagious," and they're wiping their eyes and they're blowing their nose.

Frankly, they don't know what they're talking about. They are basically a walking, talking, breathing, sneezing, coughing, cold virus vector. A vector is a route for passage of a virus. So please, if you are sneezing, if you are coughing, if you are still experiencing the symptoms of a cold, stay home, stay away from other people as much as possible.

And I realized that some people simply cannot avoid going to work or cannot avoid interacting with other family members or other people if they have the cold virus, but this mythology that if we've had a cold for a few days and we're starting to feel better, but we're still exhibiting symptoms that we're not contagious, that is pure myth.

It's simply not grounded, in fact. Now, there's nothing that can be done about that first day or two after which we're exposed to a cold virus where we are not experiencing symptoms, and it's quite possible to pass the cold virus on to other people. But I think that every workplace, every home environment, every gym, every society would benefit greatly if people who were sick with the cold did not expose other people to that cold virus as much as possible.

And indeed, this is a serious issue. It's not just about a few sniffles and watery eyes. There's an enormous financial and mental health cost and physical health cost to people getting the cold. And it's not just about people who are immune compromised or elderly people. What we're generally referring to as the cold today can be mild, it can be moderate, it can also be very severe, and it can exacerbate other health issues that people have.

And we'll talk about that a little bit later and how to offset some of those health issues. Okay, so now let's talk about the flu virus. The flu virus is, as I mentioned, a virus. And just like with the cold, there are different serotypes of the flu virus. There are also different general categories of flu virus.

So you've got your A-type flu viruses, your B-type flu viruses, and your C-type flu viruses. And by the way, I'm saying flu viruses, but of course I'm referring to influenza, but it's just kind of commonplace nowadays to refer to influenza as the flu. Similar to cold viruses, the different types of flu viruses exist based on the different types of proteins that they express on their surface.

In fact, in the news over the last few years, there have been a number of different flu virus strains that have been described according to their surface protein characteristics. Things like the H1N1 virus. What is H1N1? H1N1 describes the different types of proteins that are expressed on the surface of that particular flu virus.

Now, the most common type of flu viruses are in that A category of flus. This is the type of flu that caused the Spanish flu. Now, the Spanish flu, which by the way, did not originate in Spain, people think it probably originated in New York or perhaps elsewhere, but certainly not in Spain, killed anywhere from 17 to 50 million people, depending on which literature you read.

That's an enormous number of people. And it occurred in four different waves of infection that occurred between the years 1918 and 1920. The Spanish flu was a type A H1N1 virus. And actually, it's worth noting that this winter season, there have been some cases of H1N1 already reported in the United States and elsewhere.

Now, of course, the goal is always to contain the propagation of those flu viruses. And that is done through a number of different approaches. The best and most reliable approach, of course, is to not come into contact with somebody that is carrying the H1N1 or any other type of flu virus.

However, based on the way that the flu virus infects the body, the way that the symptoms emerge, and the ways that viruses propagate, that can't always be avoided. One thing to know, and I consider this a fortunate aspect of flu virus biology, is that the flu virus, unlike the cold virus, can only exist on surfaces for about two hours.

After about two hours, it tends to die off. So the flu virus is most typically passed by human-human contact, or coming into contact that is walking into a cloud of somebody's sneeze that contains flu virus, or somebody's cough that contains flu virus. And yes, it is possible that shaking someone's hand could actually introduce flu virus to your hand, and then if you wipe your eyes, or I'll talk about a few other portals of entry for the flu virus and cold virus in a few minutes, can get into your body and infect you.

And yes, you can pick up the flu virus from surfaces. However, that is far less common than the flu virus passing from human-human contact. Now, there aren't as many different types of flu virus as there are types of cold virus, and that's why there have been attempts at making flu vaccines, or so-called flu shots.

I think most people are familiar with the signs and advertisements online and in the workplace and school saying, "Get your flu shot this season." The reason that flu shots can exist at all is because there are limited enough types of flu virus present in a given year that specific vaccines, that is flu shots, can be generated against that particular strain of the flu virus.

So how effective is the flu shot? And I want to be very specific here. When we say the flu shot, singular, it sort of implies that there's one flu shot that can combat all the different types of flu. And as you just learned, that is not the case. So we probably should be saying the flu shots, but just for sake of simplicity, when I say the flu shot, I mean the flu shot that's given in a given flu season that is directed at specific strains of the flu, because researchers have determined that that particular strain of flu or strains of flu are the ones that are most abundant for that particular flu season.

Studies have shown that getting the flu shot reduces one's risk of contracting the particular flu that is most abundant that season by about 40 to 60%. But of course, the flu shot is completely ineffective at combating any other forms of the flu virus, and of course, colds or other types of upper respiratory infections.

Studies have also shown that taking the flu shot can reduce the severity of one's symptoms if they in fact get the flu anyway. Now, personally, I don't typically get the flu shot. And the reason for that is that I don't tend to go into environments where I am particularly susceptible to getting the flu.

I don't work in a hospital or a clinic. I don't tend to interact with large numbers of people on a daily basis. So for me, I've opted not to get the flu shot. Now, that doesn't mean that I've never contracted the flu. As I mentioned earlier, I tend to get sick with a cold or flu about once every 18 to 24 months.

And the severity of that colder flu has ranged from, you know, at one point, a very high fever in one case, but typically a moderate fever and the usual symptoms of malaise that we've been discussing. And I've managed to get over those without having taken the flu shot pretty easily.

Now, of course, we also don't know that those were actually flus. Despite the distinct differences between the symptoms of cold and flu, most people don't really know whether or not they have a cold or flu. So this is another thing to think about when considering whether or not to get the flu shot.

Ultimately, because at least to my knowledge, most workplaces do not mandate that people get the flu shot. I could be wrong about certain workplaces, but my experience is that most workplaces do not mandate that people get the flu shot. When you take the flu shot, you're really hedging a bet.

You're hedging a bet against the fact that you will be or not be exposed to that particular strain of flu virus that's most abundant that season or strains of flu virus that are most abundant that season, and that the flu shot that you're taking is directed at those particular strains.

So again, in my case, I don't tend to take the flu shot, but of course you need to make the decision that's right for you. For instance, if you have family members that are immune compromised, or you work in a school, or you think that you are exposed to a lot of flus, or you're concerned about transmitting flu to any one individual or group of individuals, those are all things that need to be taken into consideration, and of course, speak to your physician.

I will also say this, which is that I mentioned that I've tended to catch colds or flus at a rate of about once every 18 to 24 months. And when I say a cold or flu, I mean a serious one, one that keeps me in bed where I have a fever and I'm sweating.

What I have done and I continue to do is because I pay pretty close attention to how well I'm sleeping or different life events, my different workouts, et cetera, and I put those into my calendar and I have a shorthand to do that, so it only takes about 30 seconds each day.

Okay, did this work out? It was kind of level seven out of 10 intensity. Got good sleep last night or poor sleep, and I know what good and poor sleep is for me. I mean, that's about the level that I'm charting these things. I have been able to go back and look at the events preceding when I've come down with a cold or flu.

Again, I don't know whether or not it was a cold or a flu, but before I got sick, and I've seen, for instance, like if I've ever done two hard workouts in a day, something I never do any longer, I've tended to get sick after that. If I've tended to do hard workouts and then expose myself to cold temperatures while traveling, especially traveling overseas, that tended to precede those colds or flus, which again, for me, are very seldom.

So it's a limited data set. This is entirely anecdotal, meaning related to my own history of getting colds or flus, but it's something that I actually recommend people do, which is to pay attention to when you first started getting symptoms, pay attention to when you got over a given what you think is a cold or flu, and then to look at what was happening in the days before in that day.

I don't think it's possible to do hyper precise forensics on a cold or flu, right? I mean, you could have gone into the gas station, put your credit card in the machine to grab a drink out of the refrigerator and picked up a cold or flu from the handle of the refrigerator or from the credit card machine, or even from the gas pump.

You simply don't know. However, if you look at the pattern of behavior, travel, sleep, exercise, sorts of interactions you were having prior to getting a bad cold or flu, chances are you're gonna learn something interesting and be able to avoid getting a serious cold or flu, at least to some extent going forward.

And I've done that, I think fairly successfully because I can tell you that the frequency of colds or flus that I've come down with has indeed been dropping from year to year. So whereas a decade ago, I tended to get colds or flus probably about once a year, and in some cases even twice a year, although that was pretty rare, that really expanded to about once every 18 months.

And then in the last five years, I think I've gotten sick two times pretty badly with a cold or flu, and then once with a kind of mild cold or flu. So I tell you all that just as an example of how you can start to think about how your immune system interacts with different types of behaviors, different types of situations, such that you can learn something about your immune system and what's going to best protect you against getting colds and flus going forward, which of course is a great thing to do because we all think that we can get out there, be around people that are coughing and sneezing.

We can go to the gym when it's crowded in winter. Oh, that person over there is coughing, but I'm going to just stay a few feet away, no big deal. And while I don't want to turn anyone into hypochondriacs, that's how you get infected. That's how you get a cold or flu.

And at the same time, I don't think anyone should get to the point where they're afraid to go into a gym or afraid to go to the workplace. But I will say once again, if you're sick with a cold or flu, if you are coughing, sneezing, blowing your nose, runny eyes, and you're walking into work or the gym or onto public transportation, and you're telling people I'm not contagious, you're lying.

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To try AG1, go to drinkag1.com/huberman and you'll get a year's supply of vitamin D3K2 and five free travel packs of AG1. Again, that's drinkag1.com/huberman. Now, the diabolical thing about the flu virus is that just like the diabolical thing about the cold virus, you start shedding virus, that is you are contagious, about 24 hours prior to the onset of first symptoms for you.

So that means that you can be a flu viral vector even when you aren't having symptoms. That's just the unfortunate aspect of these viruses. They're very clever. They don't have brains, but these viruses have adapted to propagate from host to host to host. They have a drive to continue to stay alive and to infect more hosts.

So even though they don't have a brain, they have a sort of, let's call it viral intelligence. And as I've said several times now, if you are still exhibiting symptoms of the cold or flu, you are contagious. However, with respect to the flu, you are most contagious during the three days when you feel the absolute worst, when your fever is at its worst.

We'll talk about how to deal with fever a little bit later. When you are coughing and sneezing, headache, all of that, when that is at its peak, that is when you are most contagious. So again, I realized that people can't always avoid contact with other people, you know, you live under the same roof, caretakers interacting with the person that has the cold or flu.

And I do want to remind you something I said earlier, which is just because you come into contact with a cold or flu does not necessarily mean that you will come down with that is be infected by a cold or flu. Whether or not you come down with a cold or flu is of course dependent on whether or not you come into contact with it.

You can't catch a cold or flu that you've never come into contact with, just like you can't get eaten by a shark if you never go in the ocean. However, the probability of coming down with that cold or flu, of it getting past your immune system barriers and infecting you is going to be strongly dictated by the different aspects of your immune system for which there are three major aspects, which we'll talk about next.

And of course, the things that you do to bolster those three aspects of your immune system. Okay, let's talk about your immune system. And I have to confess that even though I've spent well over three decades being a student of and researcher of the nervous system, the immune system is oh so cool.

And I say that because it has this incredible elegance and logic to it. It basically consists of three major lines of defense. There's a physical barrier or rather a set of physical barriers that exist between the organs of your body and the outside world. And you're probably immediately thinking skin.

And yes, indeed, it includes your skin, but also some interesting things like the mucosal lining of your nose and mouth, and even some of the liquids that are on the surface of your eyes. We'll talk about those in a moment. Then there's a second line of defense, which is for any virus or bacteria or fungus for that matter, but today we're talking about viruses, cold and flu viruses.

Any viruses that get past the physical barrier of your skin and the mucosal lining of particular regions of your body, well then you have what's called the innate immune system. The innate immune system is this very generalized response system. It's general in the sense that it deploys a basic set of neurochemicals that are not specific to the particular virus that's made it into your body.

So not only is it not specific to a particular serotype of the cold or a different type of flu virus, but it's not even discriminating between cold or flu virus. This thing we call the innate immune system is a generalized response system to go and combat viruses. So it could be a cold, it could be a flu, it could be a bacteria, it could be a fungus, it could even be a physical object, and your innate immune system responds by saying, "Okay, let's go deal with this." Now, the third component of your immune system is what's called the adaptive immune system, and I alluded to this aspect of your immune system a little bit earlier.

The adaptive immune system is the aspect of your immune system that recognizes, because the innate immune system told it, that something has infected the body at some level, at some organ or set of organs, and there's an emergency. And the adaptive immune system goes in and in a very targeted way, figures out what sorts of proteins it needs to produce, that is antibodies, to combat that specific serotype of virus.

Okay, so the immune system has a physical barrier component, and it's not just skin, some other things as well. You've got your innate immune system, which is this generalized response system, and then there's the adaptive immune system. Let's talk about the physical barrier component first. And this is actually a good opportunity for us to just take a brief step back and realize that anytime we're talking about our physiology, there's going to be a mechanical set of features, and there's going to be a chemical set of features.

So right now we're talking about the immune system, and the mechanical feature, or the physical feature of the immune system, is this barrier between the organs of our body and the outside world. And the most obvious of those is the skin. You are contained in this bag of stuff that we call skin.

The skin isn't just for putting clothing on and for adorning with jewelry or tattoos, if that's your thing, watches, et cetera. Your skin is a living organ in and of itself. I think we're most accustomed to thinking about the heart and the lungs and the liver and the brain as organs of the body, but the skin is an organ of the body as well.

It has a bunch of different layers of cells from the outside to the inside. Actually, the skin cells themselves are made in the deeper layers of the skin, and they migrate out towards the surface of the skin, and at the surface of the skin, on top of those cells and made by those cells are different types of chemicals that actually serve as antibacterial and antiviral agents, meaning if a cold virus or flu virus or other type of virus lands on the skin, it can neutralize and kill that virus.

So your skin is a very important physical barrier against viruses such as the cold or flu virus getting into your body and infecting other cells and tissues. Now, your skin is not contiguous, meaning there are holes in it. So let's think about those holes for a second. As we go from head to foot, it's pretty obvious that your eyes have these two openings, and those are openings in your skin, right?

As you open your eyelids, beneath there are your corneas, the shiny part of your eyes, and then a little bit further back, at the back inner lining of your eyeball, you have a very thin three-cell layer thick piece of tissue that we call the neural retina. And I say this because the neural retina is actually a piece of your brain.

So you have two pieces of brain that line the back of your eyes, and that's the light sensing tissue in the back of your eyes. Now, I say this because what this means is that it's a very short distance between the opening of your skin that we call your eyelids and your brain.

Now, most of the brain, of course, is contained in the cranial vault within what most people call the skull, but your brain isn't far away from those openings that we call your eyelids. So as a consequence, on the surface of your eyes, those corneas, the shiny part of your eyes on the outside, there are a bunch of different chemical features.

There are tears that are made by your lacrimal glands, but there are also a lot of antibacterial agents that actively kill off stuff that could potentially infect your body, could make it into your body, maybe even into your brain. If you've ever woken up in the morning and you have some crust on your eyes, and you look at that crust, that kind of yellowy stuff, sometimes it's yellow, I know this is kind of gross, that's actually dead bacteria that your eyes have successfully defeated during your night's sleep.

So when you wipe those away, you're taking the casualties of a war that you won during your night's sleep, and you're whisking those away. Now, as we descend a little bit further down the face, there are, of course, the nostril openings, and the nostril openings tend to be kind of sticky, right?

They're moist, sticky, and warm. You don't have to put your fingers up them right now, you just know they're moist, sticky, and warm. Get your fingers out of your nose, please. The mucosal lining of your nose is actually a very important substance that is sticky in order to trap viruses such as colds and flu viruses, and then chemical components within the mucosal lining can neutralize them.

That's the best case scenario. There are, of course, scenarios in which the cold or flu virus takes residence in your mucosal lining and it can make its way back into your sinus passages and can then infect other cells and tissues of your body because the virus replicates and spreads throughout the body.

And then going a little bit further down, I realize this is obvious, you have your mouth. And what's really interesting is that your mouth also has mucosal lining, which is sticky, and it has chemical components to neutralize incoming viruses. But we know that the type of mucus and the type of bacteria that live in your nose and mouth that, by the way, are very healthy for you and encourage healthy immune system function, that is, act as ways to neutralize viruses within your nose and mouth, are very different.

So your nose and your mouth, they seem similar at the level of, okay, well, it's warm and sticky in there, there's mucus, but they are very, very different tissues. In fact, if you think about your mouth, it's this incredible structure that not only lets you eat and breathe in and out through, although I suggest most people be nasal breathers for most of the time of their day and night, if you can.

Of course, sometimes you have to mouth breathe. But keep this in mind, you have this big opening in the front of your face and bacteria are getting in there all day long. Viruses are getting in there all day long. And in most cases, you are successfully combating those viruses and bacteria because the mucosal lining of your mouth and your nose for that matter, and the microbiota, those little microorganisms that have taken residence in your nose and mouth are helping to contribute to fight off bacteria and viruses, provided the microbiota there are diverse and are of the type you want, which we'll talk a little bit more about later.

And then descending further down the body, of course, there are other openings into your skin barrier, namely the urethra of the penis or vagina, and of course the vaginal canal. So the genitals, of course, have their own mucosal lining. And as you can imagine, it is distinct in terms of its physical makeup and its chemical makeup from the mucosal lining of your nasal passages and mouth.

And then of course we have the rectum and anus, which is the outflow pathway of your intestines, which are post-digestive. And there too, you have a mucosal lining for which, yes, certain types of viruses and bacteria can infect that area. But what we know is that the primary entry sites, the most common ways in which colds and flus get into your body, the way they breach that physical barrier that we call your skin, is through your eyes, your nose, or your mouth.

And there are a lot of data, some of which conflict, and frankly, there need to be more data in order to really resolve this, but it seems like the primary entry site for viruses to get into the body tends to be the eyes or the mouth. And we can get into some of the reasons why that would be so.

But if you think back to our conversation about the way that colds and flus exist in the world, either as aerosols or on surfaces of objects or on surfaces of skin, well then what I'm about to tell you next will make it oh so obvious why the eyes and the mouth are the primary sites of entry for colds and flus.

And if you keep that in mind, there's a good chance you can avoid a lot of colds or flus that you would otherwise catch. Okay, so before I talk about the important roles of the innate and the adaptive immune system in keeping colds and flus at bay, I'll tell you that you have a problem.

And that problem is that you tend to touch your eyes very often. In fact, you tend to touch your eyes most often after you shook somebody else's hand. Now, why am I picking on you? Well, in fact, I'm not. I'm picking on all of you and I'm picking on myself included because there have been several studies now, primarily from Noam Sobel's lab at the Weizmann Institute showing that when people encounter another person and they shake their hand, they either touch their eyes or touch another region of their face very close to the eyes or that they touched their hand to their mouth.

Now, there are a bunch of theories as to why people do this. There's the idea that people are actually sniffing their own hand and in particular sniffing their own hand more often after they shake someone else's hand as a way to detect what chemo signals exist on the other person, not necessarily conscious smelling of the other person's smell, but rather some sort of unconscious mechanism by which we take the chemicals of the person we come into contact with and we bring them to our nose, our eyes, or in some cases our upper lip.

And that our olfactory system, that is the neurons that exist just behind the back of our nose are processing that information and getting all sorts of important information about how stressed the other person is, their hormones, whether or not we recognize them, the fact that they are different from us, that's right.

We are also smelling ourselves all day long. Noam's lab has shown this, that people are kind of walking around in their own odor cloud. We tend to touch our armpits. We tend to touch different aspects of our body, yes, and smell ourselves multiple times throughout the day. This is all being done unconsciously.

I suppose some people are doing it consciously. And that there's a lot of information about our physiology and health. And when we do this after shaking somebody's hand, that there's a lot of information about the other person's physiology and health, that our nervous system, our olfactory system and deep parts of our brain that are involved in primitive type behaviors, but also some pretty sophisticated behaviors are taking into account.

Now, Noam Sobel was a guest on the Huberman Lab Podcast. I encourage you to check out that episode if you have time. It's a fascinating voyage into the olfactory system and not just conscious smelling or sniffing of things. So we go, oh, that smells good, or that smells bad, or that person is somebody I want to mate with or hang out with or avoid.

It's also unconscious processing of so-called chemo signals, chemical signals. But the reason I'm bringing up these studies now in the context of colds and flus and how to avoid getting colds and flus is as a reminder that we are pretty much wired to contact our own face with our own hands at the level of our eyes, nose, and upper lip and around the eyes very shortly after we touch somebody else's skin.

And if you are mindful of it, you can actually avoid bringing colds or flus to your face. Now, in doing so, or you're going to short circuit a bunch of other important biological processes involved in understanding what's going on in your environment because you're not bringing in those smells, I suppose that's possible.

But with respect to avoiding colds and flus, it seems like a pretty good trade off to me. So the point that I'm trying to make here is that in order for you to catch a cold or flu, that cold or flu virus, the little particles of cold and flu virus need to make it into your body.

And the primary entry sites are eyes, nose, mouth, and the primary actions by which we bring colds and flu viruses to our eyes, nose, mouth are by touching other people or by touching other surfaces that have cold or flu virus. Just to remind you, cold virus can exist up to 24 hours on a given surface.

Flu virus tends to die off after about two hours on a given surface. And we're bringing that to our face. We are literally bringing the virus to ourselves. So a little bit more conscious awareness about that fact means that you can probably avoid colds and flus to some extent.

How much? Well, it's unclear. It's unclear because as you recall, some people have and are passing along cold or flu virus prior to any symptoms. And of course, it's possible that you can walk into an aerosol cloud of cold or flu virus even if a person isn't there and you don't come into contact with them.

But some conscious awareness of these routes of passage for the cold or flu virus, I do believe can reduce the probability that you will catch a cold or flu. And of course, I'm not encouraging people to never touch. Touch is an important part of social connection and social bonding.

But if you start to think about these portals of entry for the cold and flu virus into your body, well, then you perhaps might think twice before hugging someone, kissing them on the cheek during a time in which you're trying to actively avoid getting the cold or flu. Now, I feel a little bit funny about sharing this information because again, I don't want to encourage people to always be at arms distance, fake fist bumping, keeping a gap between them.

Again, touch is an important component of social connection. But since today's topic is colds and flus and how to avoid getting colds and flus, just like you can't get eaten by a shark if you don't go in the ocean, there's a much lower probability that you're going to get a cold or flu if you're not touching a lot of hands and bringing those hands to your eyes, nose or mouth.

I suppose one way around the sort of do I hug, do I shake hands thing is to just be conscious of the fact that when you shake somebody's hand that you're very likely to touch your eyes or face within the next 30 seconds or so. And maybe you end up being that person who puts some hand sanitizer on your hands.

Sometimes that can feel a little awkward to do that right in front of somebody. You know, it's kind of sending a signal like, hey, I don't want you to infect me, but guess what? You don't want them to infect you. Okay, let's imagine that a cold or flu virus makes it into your system.

It breaches the physical barrier of your skin and mucosal lining. Now, you have in mind all the different ways that could happen and all the different ways that could be prevented. But we are starting at a point here, a hypothetical point whereby that cold or flu virus has made it into your body.

Your immune system has an absolutely exquisitely sophisticated way of knowing you versus other, meaning cells within your body that are of you and cells of your body that are from other organisms or viruses from the outside world. And when viruses such as a cold or flu virus are detected in your body, your body might not even recognize that it's a cold or flu virus.

It might not even recognize that it's a virus at all. It just knows that this thing that's in me is of other. It's not me. I've never seen it before. This is not me. These are not my cells. These are not the chemicals that I'm producing. And your immune system is amazing in that way.

And when it occurs, your innate immune system launches a response. What is that response? Well, first of all, the response is very rapid, right? Cold or flu makes it into your body and your innate immune system immediately or near immediately launches an attack on that invader or invaders. Because as soon as the virus gets into your body, it's going to start replicating as quickly as it can.

What happens? White blood cells that your body produces will go to the sites where those viruses are. And by the way, those viruses are basically getting into cells of your body and then hijacking the genetic machinery of those cells in order to replicate within those cells and then exit those cells and then go infect more cells.

That's how these viruses work. Your body's making white blood cells, things like neutrophils, natural killer cells, macrophages. These are what we call effector cells that act as a kind of ambulance system and go to the sites that those viruses exist and the cells that they've infected and start trying to physically barrier them in and also use specific chemical mechanisms to neutralize and kill those viruses.

Again, anytime you're thinking about biology, think of mechanical features and chemical features of a response. Now, a key component of the innate immune system is what's called the complement system. Not complement like, oh, you look very nice today, but complement, okay, the complement system, which exists in the plasma within your blood.

These are chemicals in your bloodstream that go and mark specific cells that have been infected or viruses with a signal, a chemical signal that essentially looks like an eat me signal to these other cell types of your immune system, such that those natural killer cells go through the body and go looking for the cells that have this eat me signal on them and try and destroy those particular cells.

The other thing that your innate immune system does is that the cells that have been infected and that are undergoing damage, remember, they have cold or flu virus within them and they're hijacking the cellular machinery of those cells and using it to produce their own virus, more of the virus.

And as a consequence, the genetic machinery of those cells is not able to do a bunch of other things that it normally can do, or at least not as well. Well, those cells that are really hurting release a help me signal. And then in response to that help me signal, your immune system releases what are called cytokines, things like interleukin-1, interleukin-6, tumor necrosis factor alpha, just fancy nerd speak names for different types of molecules that go to the site of infection and try to help or assist to remove that infection.

And they also try to assist the repair of the cells that have been infected by those viruses. Now, one of the mechanical or physical consequences of these chemical signals like interleukin-1, interleukin-6, TNF alpha, again, those are all cytokines, being drawn to a particular cell or region of cells that have been infected is that it creates some physical swelling of the area.

It impacts the vasculature, the veins and capillaries that feed that area. And in response to that, they put more blood there so you get some swelling or you'll get, in some cases, the release of histamines, right? We think of antihistamine drugs. Well, histamines are an aspect of your immune system.

They move around in your body in these really cool cells called mast cells, M-A-S-T, mast cells. And when the histamines are released, that area becomes kind of hot and swelling. It's what we call edema. And that whole area is marked as really a site, just like a crash site on the side of the road.

It's like, hey, we've got eat me signals to get the debris and the bad stuff out of here. Try to get those viruses out of here. We've got help me signals to try and help the injured cells, just like you would try and help people at a car crash.

And there's a bunch of swelling, so there's additional blood flow. Sometimes there's some other physical features as well. Now, the important thing to know is that the innate immune system is very fast and it is agnostic to the type of infection. In fact, it doesn't even matter if it's a bacterial, physical, fungal, or viral infection, but it certainly isn't paying attention to the exact serotype of cold virus or whether or not it's an H1 influenza or another type of influenza.

So the way to think about the innate immune system is that it is a very fast and nonspecific response to a viral or other type of invader. Now, that's all a bunch of biology, but if you think about it, let's imagine a scenario where you go to a party, hang out at the party, you don't see anyone coughing or sneezing, but maybe one person there has a cold virus or they have a flu virus and they aren't even aware of it.

They're not going to come down with symptoms for another day or so. You talk to that person, you shake hands, maybe touch your eyes, maybe you don't, but you're exposed to that cold or flu virus. You go home, you go to sleep, you wake up the next morning, you feel fine.

And then sometime in the next afternoon, you start to feel a little tickle in your throat and you start to feel just a little bit of fatigue or malaise. Do you have that cold or flu? Well, possibly, okay, we don't know for sure, but assuming that that cold or flu virus did indeed make it into your system, then your innate immune system is starting to create a set of responses that we talked about a moment ago, but it also tends to impact things at the level of your brain, such that you kind of feel like, I don't feel quite right.

I feel like a little bit, I don't feel great. And there are a lot of reasons why you would feel that way, and we'll talk about those reasons a little bit later, but does that mean that you're necessarily coming down with a cold or flu? Well, technically, yes. Your innate immune system is deployed to fight this foreign viral invader, but whether or not you actually get a full-blown cold or flu or put differently, how severe that cold or flu infection is, it depends on whether or not your innate immune system can fight off that cold or flu at the outset.

And indeed, there are many cases, we believe, where you get exposed to a cold or flu, it makes it into your body, but your innate immune system is sufficient to beat it, to fight it back. This is one of the reasons why it's so important that if you're starting to feel a bit under the weather and you think you're coming down with a cold or flu, that you do certain things in order to make sure that your innate immune system is both ready and that it can launch a full-scale attack on that cold or flu virus.

We're going to talk about how to do that a little bit later. I'm not trying to withhold. It's just, it's important to understand that just because the virus makes it into your body, doesn't necessarily mean that you're going to get a full-blown cold or flu. And in fact, that innate immune system sometimes is sufficient to prevent that cold or flu from replicating enough that you get the full-blown set of symptoms.

And that's kind of an ideal scenario. So we're definitely going to talk today about what to do if you start to feel a little bit of malaise, what to do if you discover that, oh, you know that person I was hanging out with at the party the night before, they're really sick with a cold or flu.

Because there are things you can do to increase the probability that your innate immune system can handle the battle sufficiently such that you never have to get to the next component of the immune response, which is the adaptive immune response. I'd like to take a quick break and thank our sponsor, InsideTracker.

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If you'd like to try InsideTracker, you can go to insidetracker.com/huberman to get 20% off any of InsideTracker's plans. Again, that's insidetracker.com/huberman. Okay, so the third layer of your immune system is your adaptive immune system, and this is an amazing aspect of you, okay? The stuff we talked about up until now, the physical barrier, the innate immune system, so, so cool, but the adaptive immune system is really a mindblower.

The most important thing to understand about your adaptive immune system is that as the name suggests, its job is to create antibodies specific to the very intruder that made it into you and infected your cells, the very specific serotype of cold virus, the very specific type of influenza, such that you defeat that virus, but then in an amazing way, your adaptive immune system also maintains a memory of that battle and keeps within your body, believe it or not, within a population of stem cells, which are cells that can rise to more cells, such that if you ever encounter that same serotype of cold virus or same strain of influenza again, that your antibodies can immediately neutralize that colder flu virus.

The adaptive immune system has the ability to make proteins that have a particular shape on their surface that matches the shape of the thing that your immune system is trying to kill. Now, the adaptive immune system has two basic phases. In the first phase, the adaptive immune system makes these things called immunoglobulins, IGs, and the immunoglobulins come in different forms.

There's IgG, there's IgM, there are other types of IGs as well. For sake of today's discussion, know that the initial wave of antibodies that the adaptive immune system makes are of the IgM variety and the IgM antibodies can travel to and latch onto the surface of the colder flu virus and it matches it pretty well.

It's not perfect, but it matches it pretty well. Think about, for instance, a particular serotype of cold virus or the H1N1 flu virus having a very particular contour on its surface. The IgM approximates that contour such that it's better at fighting that cold or flu virus than is the innate immune system, but it's not a perfect fit.

However, the adaptive immune system doesn't stop with the production of those IgMs. The adaptive immune system takes that information about how precise or imprecise that fit is between the IgM antibody and the surface of that particular cold or flu virus, and then, in an amazing way, sends signals back to the stem cell populations in the bone marrow and other tissues, and then more antibodies come out of the IgG variety, and the IgG proteins are very specific to the shape of that particular cold virus or flu virus, such that the IgGs then can define to and neutralize those viral particles, okay?

So when we talk about the immune system, we're talking about a physical barrier that, if it is breached, a cold or flu virus takes residence and starts to replicate. The innate immune system launches a generalized attack on that cold or flu virus, and then the adaptive immune system kicks in usually a couple days later, first with the production of antibodies that are pretty specific to the particular virus that happened to make it into the body and infect cells, but then there's a second wave of production of antibodies, and those antibodies are incredibly specific for that particular cold or flu virus, and, as I mentioned earlier, the adaptive immune system then acquires a memory of the specific fit between a given antibody that it made and the viral invader and the successful battle that those antibodies waged on that viral invader, and that memory is maintained such that, if the next week or the next season, you encounter the exact same serotype of cold virus or same type of flu virus, well, then you already have antibodies ready to be deployed.

Sometimes the antibodies continue to circulate in your system. Sometimes you need to generate more of them, and the immune system is that amazing. It can actually send a message back to that stem cell population in the bone marrow or elsewhere, say, "Hey, listen, this virus that we beat a few weeks or months or years back, it's back.

We need more antibodies," and boom, your adaptive immune system churns those antibodies out and kills the virus. Now, as a final point about the immune system, I've been talking a lot today about cells traveling to and killing viruses and sending signals, "Eat me, help me," et cetera. It's important to understand that, while cells can migrate through the body, a lot of what we're talking about here is the movement of proteins through the vascular, through the blood system of the body, but there's another system that's very important for all of this that's collaborating with the vascular system, and that's the lymphatic system, and we don't have time to go into a whole lecture about the lymphatic system, but suffice to say, the lymphatic system can pull stuff from the blood, such as viruses, but also cells that have been beaten up or cells that have been eaten and are contained within other cells, such as macrophages, and it can do some filtering of those different cell types, and it can produce its own useful chemicals that then can be reintroduced to the bloodstream in order to help combat the infection.

Now, this becomes very important when later we talk about how specific forms, intensities, and durations of exercise can increase the ability for your innate immune system to combat infections so that your adaptive immune system perhaps doesn't even have to get involved in the battle because your innate system handled it.

There are data to show the exercise of sufficient intensity and duration, but not excessive intensity and duration, can recruit the lymphatic system and recruit or increase the activity of the innate immune system even in the absence of an infection, such that if you go to that party and you encounter that person with a cold or flu, you can defeat that cold or flu virus at the outset and never have to deal with making antibodies to that cold or flu virus at all.

Okay, so now you have a fairly sophisticated biological understanding of what colds are, what flus are, and the way that your immune system works to fight off viruses like colds and flus. So with that in mind, I think now is the appropriate time to start talking about what the scientific peer-reviewed research says about how to allow your immune system to function at its best such that you can combat colds and flus.

Meaning, if you are exposed to a cold or flu, that is if it breaches that physical barrier of your skin and the mucosal lining of your nose, your mouth, or it gets into your eyes, that you stand the greatest chance of defeating that cold or flu at the level of your innate immune system, such that your adaptive immune system never even has to respond to it by creating all those specific antibodies.

Now, fortunately, there are a lot of different things we can do to improve the function of our immune system. In fact, I feel like any time the winter months roll around, we start to see the same list of things surface online and in the press. And I don't want to diminish these things.

They are in fact the bedrock of maintaining and enhancing the function of your innate immune system. So what are those? Well, some of these will be pretty obvious, things like getting enough quality sleep each night. We know, for instance, that if you're sleep deprived, so especially if you stay up all night, but certainly even if you only get 50% or 75% of your sleep requirement, that your innate immune system is going to suffer.

It's not going to be as effective at combating flus or colds. In addition to that, we know that exercise of specific type and specific duration and specific intensity can serve to bolster the innate immune system. And we'll talk about the specific exercise protocols that can best achieve that. We also hear, and it's absolutely true, that we need adequate nutrition.

If we are in a caloric deficit, for instance, if we're trying to diet through the winter months, which many people try to do, that can place our innate immune system in a bit of a compromised state. That said, things like intermittent fasting or even longer duration fasts have been implicated, and here I really want to underscore implicated, in brief improvements in the function of the innate immune system.

However, extended fasts or not eating enough calories to maintain body weight for many, many days in a row can actually compromise the function of the innate immune system. I'll go into this a bit deeper in a moment. And then of course, we hear about stress, that we're all supposed to regulate our levels of stress, not get too stressed.

And here I have to put an asterisk next to those statements because yes, indeed, chronic stress, meaning stress that continues day after day after day, or even short periods of stress that impede our ability to sleep at night, can indeed reduce the functioning of our innate immune system. However, it's also clear that short bouts of stress, provided that they don't inhibit our ability to sleep that night, can actually enhance the function of the immune system.

And this is something that I don't think is talked about enough. You know, we hear so often that quote unquote, "Cortisol is bad, it's a stress hormone." Listen, cortisol is fantastic, provided that it is elevated early in the day and not late in the day or evening. Also, cortisol does have thresholds beyond which if it's too high, can be bad for us.

But it's also the case that if cortisol levels are too low, that's bad for us, and it's especially bad for the functioning of our immune system because glucocorticoids, of which cortisol is, have an important role in activating those natural killer cells of the innate immune system. They are one of the primary signals by which those interleukins, like interleukin-1 and interleukin-6, are deployed in our body.

And so very often we'll hear stress increases inflammation, and indeed interleukin-1 and interleukin-6 are pro-inflammatory. You might think, "Oh my goodness, I don't want that. I don't want cortisol. I don't want these interleukins elevated." But guess what? The inflammation response is also an important component of that innate immune system that allows us to combat infections.

So in trying to keep our innate immune system tuned up, I realize that's not a biological statement, tuned up, but keep our immune system functioning at its best, we want inflammation available as a tool to combat infection. We want cortisol available as a way to activate that inflammation and other aspects of our immune system.

We just don't want so much cortisol and so much inflammation that we can't sleep and that our gut microbiome suffers. And that brings me to the other component that's important for the basic functioning of your innate immune system so that you can be at your strongest when you inevitably encounter those cold and flu viruses.

Why do I say inevitably? Look, if you exist in the world, that is, if you live on planet earth, you are going to be bombarded with different viruses and bacteria and funguses and all this stuff throughout your days. And yes, in those winter months, because people are spending more time indoors and they're touching each other and surfaces more, breathing on each other more, sneezing on each other more, and so on and so forth, there is more propagation of colds and flus.

So if we take a step back and we ask, "How can I have my immune system as strong and ready as possible to combat cold and flu viruses?" We get to those basics. It's make sure you're getting enough quality sleep each night. How much is enough? However much you need in order to not feel sleepy during the day, except maybe the requirement for a short nap of anywhere from 10 to 30 minutes.

Not everyone requires that, but that's perfectly normal to have an afternoon dip in energy that can be restored with a short nap or non-sleep deep rest. We'll provide links to non-sleep deep rest and other tools in the show note captions that are zero cost tools to allow you to recover your energy.

Some people just simply take a nap and that sort of thing. If you want tools for improving your sleep and making sure that you're getting enough quality sleep each night, we will also provide a link to our zero cost sleep toolkit that details that in PDF form. It just lists out the things that you can do or take if that's your choice and so on and so forth.

And of course we've done episodes on quality nutrition and what that means. We've done episodes on stress and how to combat stress, and we've done episodes on the so-called gut microbiome. But right now, I just want to mention that the gut microbiome, which are the trillions of little micro bacteria that interact heavily with the immune system and help support the immune system, you want to keep the gut microbiome healthy.

So you'll notice that we include some tools related to the gut microbiome here in a moment. And this is very important. Keep in mind that the microbiome doesn't just exist in the gut. So often these days we hear about the gut microbiome and I'm oh so happy that the gut microbiome is getting the attention that it deserves in the context of mental health, physical health and performance.

But we can't forget that the microbiome also exists on the surface of the eyes and in the nasal passages. And indeed the microbiome that's specific to the nasal passages, as I mentioned before, is very different from the microbiome that exists within the mouth. And the microbiome that exists within the mucosa of the nasal passages seems to be the most effective at combating any viruses that we encounter, especially cold and flu viruses.

So while ideally you would never encounter a cold or flu virus, we know that if the cold or flu viruses go in through the nasal passages, you stand the greatest chance of combating that particular cold or flu. So what does that mean? This is where I get to make a strong push for being a nasal breather.

Certainly in sleep, you want to be a nasal breather, but also throughout the day, unless you're speaking or unless you're exercising hard enough that you need to breathe through your mouth or unless you're eating, being a nasal breather is known to provide the right milieu, the right environment to keep that nasal microbiome at its healthiest and to promote the diversity of microbiota in the nasal passages that can best protect you against colds and flus.

And there are a growing number of studies that point to this fact. I'll provide a link to one that I like very much, which is entitled "Alterations in Oral Nasal Pharyngeal "Microbiota and Salivary Proteins "in Mouth-Breathing Children." This is but one study pointing to the fact that being a nasal breather is a good thing.

Mouth-breathing children and mouth-breathing adults, meaning children and adults that default to mouth-breathing tend to get more infections of the upper respiratory tract, including colds and flus. Consciously focusing on nasal breathing is one of the best things that we can all do to combat any colds or flus that we might encounter.

So earlier we talked about trying to avoid touching your eyes, at least without washing your hands first or sanitizing your hands first after you meet somebody, keeping in mind that most people do that unconsciously. Here we are also saying when you enter a room, you're hanging out with people, maybe you're waiting for public transportation or you're at work or walking down the hallway, unless you are exercising hard, unless you are talking, try to focus on being a nasal breather.

There are a bunch of other reasons to be a nasal breather as well, but this is one of the primary ones. And I'll provide a link to another reference, which is the book "Jaws" by my colleagues at Stanford, which talks about nasal breathing and the importance of nasal breathing, but also the degree to which children and adults open themselves up to increased levels of viral infections, as well as bacterial infections, but viral infections in particular, when they rely on mouth-breathing and the incredible benefits of doing this very simple, zero cost thing of whenever you can consciously remember to breathing through your nose, as opposed to breathing through your mouth.

And just as an additional point about nasal breathing, because I can't resist telling you this, I just think it's so cool, such an interesting adaptation. When we breathe through our nose, we heat the air in a way that's very different from the way we heat the air when we mouth breathe.

And by heating the air that's coming into the nasal passages, it shifts the probability that cold or flu viruses will successfully embed in the mucosal lining and infect the underlying cells and get into the other cells and tissues of our body. So this whole thing about nasal breathing is important and effective at the level of temperature regulation of the milieu within the nose, and therefore the viruses that end up in the nose, as well as the mucosal lining, the chemicals made by the mucosal lining.

And again, the nose is a very different place than the mouth. In fact, I'll provide a link to yet another paper, which is entitled Human Nasal Microbiota. It's a really interesting paper. It's actually an interview with a scientist who's expert in the nasal microbiome, talking about how this structure within our nose really is the primary defense site by which we destroy potentially incoming viruses.

So if it sounds overly simple, just breathe through your nose. It is very simple, but it's also very effective. Now it's also clearly the case that keeping your gut microbiome is advantageous for keeping your innate immune system at its most robust level of functioning. And I should mention that your gut microbiome isn't just about your stomach.

You know, we hear the word gut and we think stomach, but it's actually the entire length of your digestive tract from your mouth out the other end. And different microbiota exist at different locations along that tract of mucosa. And there are a couple of things that one can do in order to make sure that the gut microbiome is best supported along that entire length.

The first one is that, and this was covered on the episode that we did with my colleague, Justin Sonnenberg, who is a world expert in the gut microbiome. And that is to consume anywhere from two to four servings of low sugar fermented foods per day. So things like sauerkraut, things like kimchi, things like kefir, things like kombucha.

It can be a little bit of work to figure out which of these you like and which ones you're willing to consume on a regular basis. But it's very clear that the brine, you know, that kind of a salty solution around the sauerkraut, and by the way, when I say sauerkraut, what we're talking about here is the type that has to be refrigerated.

It contains what are called live cultures as opposed to the sauerkraut that can exist in the non-refrigerated portion of the store. Or pickles that also have that brine and that have to be kept in the refrigerator even before they're opened. And of course, things like yogurt, which have active live cultures.

Those are the sorts of things that are going to best support the diversity of microbiota along the entire length of the gut microbiome, such that your gut microbiome can do its job in supporting your nervous system. But here, especially in the context of today's discussion, your immune system. Now, the low sugar component of low sugar fermented foods is important because what we know is that if you're consuming yogurts with a lot of sugar, or you're consuming kombucha with high levels of sugar, or you're consuming pickles or sauerkraut that have a lot of sugar in them, you're probably going to start to create some other issues related to the sugar.

What you're really looking for are these low sugar fermented foods. And they can be a little bit tricky to seek out in the store, but they're usually there. And once you identify the ones that you like, you should really aim to get two to four servings of those per day.

You can also consume a prebiotic or probiotic in the form of capsule form. Things like AG1 athletic greens also contain prebiotic, probiotic, but it's very clear that consuming two to four servings of low sugar fermented foods per day is among the best ways to promote health of the gut microbiome.

And that the gut microbiome is so, so important for keeping the innate immune system thriving, such that it can combat the colds or flus that are trying to bombard your system. Now there's another tool that you can use to enhance your gut microbiome. I have to warn you, this one might make a few of you cringe a little bit, but this is one that I actually started doing about four months ago.

It's an interesting one. It kind of dates back to some older quote unquote traditional medicine practices, but it makes really good logical sense. To be fair, I'm not aware of any randomized control trial exploring the use of this protocol, but it's so simple and completely cost-free and it stands so strongly on the logic of how the gut and oral microbiome work that frankly I started doing it and whether or not it's placebo effect or not, I don't know, but I feel better and it's so easy to do and it stands to potentially improve the function of your gut microbiome enough that I figured I would at least share it with you and then you can decide.

So what this protocol essentially consists of is before you go to sleep at night or in the morning, you pour yourself a little bit of water, whatever water you happen to consume, just clean, clear water. And then you take a sip of that water when you wake up in the morning and you swish it around in your mouth and then you swallow it.

Now for those of you that are like, oh, gross, let's think about this. Is it really gross to swish a little bit of water around in your mouth and then swallow that water when you first wake up prior to brushing your teeth, of course? Well, it might seem gross to you, but throughout the night when you're sleeping, especially if you are a nasal breather while you sleep, the environment within your mouth is such that you're breeding a lot of bacteria.

You are creating all those little microbacteria that potentially can inhabit your digestive tract and provide at least some of the substrate for the microbiota in your digestive tract to thrive. And if that seems gross to you, keep in mind, that's what having a healthy gut microbiome really is all about.

So the protocol is very simple at zero cost. You take a swig of water, swish around and swallow it. Oddly, it doesn't taste bad. In fact, it'll just taste like swallowing. And in fact, it tastes like swallowing a little bit of water. It's not as if it tastes like bad breath or something like that.

It's a very simple protocol that, again, no randomized control trials, but really stands on the logic of how the oral microbiome and the gut microbiome interact. And because what we're talking about here is supporting the function of your gut microbiome such that it supports the function of your innate immune system, such that you can avoid colds and flus.

At least to me, it seems like a pretty low bar, yes. Okay, so to bolster your innate immune system, you want to get that quality sleep as often as you possibly can. You want to support the gut microbiome in the ways that we just described. What about exercise? We hear it all the time.

Exercise is so good for us. It enhances the immune system and on and on. And listen, I'm a huge believer in exercise. I personally like to do three bouts of cardiovascular exercise per week, one long, one medium, one short. And I do three bouts of resistance training each week.

All of that, and specifically what I do is available to you as a zero cross protocol in the form of a PDF. We have a link to that in the show note captions. I also have a whole episode about foundational fitness and so on and so on. The discussion we're going to have now is about what general forms of exercise actually do support the innate immune system.

And, and this is really important, what forms of exercise actually deplete your innate immune system? This isn't talked about enough, I think. There are certain intensities and durations of exercise that make us more vulnerable to colds and flus. So we're going to discuss that. Before we do that, I want to just briefly touch into something that I hear a lot, which is the question, if I'm feeling a little bit rundown, should I exercise or not?

And to be honest, there isn't a straightforward answer to that question. It's impossible for me or for you to know whether or not you were indeed exposed to a cold or flu and you're starting to combat it at the level of your innate immune system, or whether or not you're just feeling a little bit sluggish.

However, what we do know is that if you are feeling malaise at the level of the body, like your body is feeling different, it's feeling heavier, you're feeling tired, you're feeling tired at a time of day that doesn't make sense, given your usual patterns of being tired. You're feeling tired in a way that doesn't make sense, given how much sleep you got the night before, right?

I mean, here, what we're talking about is ruling out any possible life stress, or you were up too late, or you drank caffeine at the wrong time, or something like that. What we know is that if you're feeling that general malaise across your whole body, it is fairly likely that you're coming down with something and that your best response to that would be to go home, take a hot shower or bath, I'll explain why you would want to do that in a few minutes, and then get into bed early, and even if you can't fall asleep, to just be as still and as relaxed as possible.

We know that if you push into bouts of intense activity, or even just push yourself to engage in activity when you're feeling run down at that sort of whole body level, maybe a little tickle in your throat, you are going to compromise the function of your innate immune system.

And it's very likely that you're going to get more sick than you would otherwise. So here's my suggestion. If you're starting to feel run down at the level of whole body malaise, or you just don't feel right, you're best off taking a hot shower or bath and getting into bed, or just getting into bed and trying to rest and get as much sleep, probably even a little bit of extra sleep.

And here's why. That whole body malaise, that extra fatigue that's not easily explained by other factors in your life, have to do with the fact that when your innate immune system is activated, meaning it's already combating a cold or flu, interleukin-1 and interleukin-6 have a way of interacting with a particular brain area called the dorsal raphae nucleus, which is chock-a-block full of neurons that release serotonin.

And serotonin from the dorsal raphae nucleus acts on specific regions of your hypothalamus, areas like the preoptic region, for those of you that want to know, and other areas of the hypothalamus that generate a state of sleepiness. In addition, when we are getting sick, our sleep patterns change. We feel like we need to sleep more, but we don't feel as rested from that sleep.

And that has to do with the ways that serotonin interacts with some of the components of the brain circuitry involved in sleep that controls slow wave or deep sleep. And this is a whole discussion unto itself. I actually covered a lot of the mechanistic aspects of this business of immune-induced sleepiness and malaise associated with feeling sick in an episode about interactions between the neural and immune system that I will also provide a link to in the show note captions.

But suffice to say, if you're feeling that whole body malaise, and especially if you also have a little bit of a throat tickle, you're just not feeling right for you, you're not accustomed to feeling that way at that time of day or night, well, then I encourage you to get rest because chances are you're already combating an infection.

However, if you are out and about a lot during the winter months, or you're interacting with a lot of people by virtue of work or public transportation or whatever, the gym, et cetera, or you're a school teacher, maybe your kids are coming home with colds and flus, and you're not yet feeling that malaise, you're not feeling any throat tickle, you're not getting that kind of burning or tickle within your nasal passages when you breathe.

We're all familiar with these things, the watering of the eyes that kind of precedes getting the full-blown cold or flu. Well, if you're not experiencing that stuff and you want to keep your innate immune system strong and able to combat off colds and flus, then we know that exercise can be an excellent way to increase the output of that innate immune system.

What I mean by that is the appropriate intensity and duration of exercise can act as a stressor that promotes a bit of inflammation, yes, the release of cytokines, and a bit of activation of the innate immune system, including the production of more white blood cells, natural killer cells, such that you're sort of prompting the innate immune system to almost think that there's something to battle such that if you ever encounter an infection, you can defeat it right off the bat.

So we're going to get granular here about what we mean by proper intensity and duration of exercise. There's a wonderful review that was published in 2019 in the Journal of Sport and Health Science entitled "The Compelling Link Between Physical Activity and the Body's Defense System." And there's a lot to this review article, but I'll just highlight a few of the critical features that are going to directly relate to protocols that I think all of you are going to be interested in.

First of all, we know that exercise that's of 60 minutes in duration or less, and that is intense, but not all out effort, okay? Here, we're not talking about percentage of single repetition max weight. Here, we're not talking about 70 to 85% of one's VO2 max. What we're talking about is you subjectively gauging what is a 10 out of 10 effort?

Like you could not do any more. You could not contribute any more effort to that exercise bout. And that's true whether or not we're talking about resistance training exercise or cardiovascular exercise like running or rowing or things of that sort. What we know is that if you do that sort of exercise for about 60 minutes or less, you promote the exchange of components between the blood and the lymphatic system that increase the circulation of those cells and chemicals within the innate immune system, such that not just during exercise, but for many, many hours afterwards, maybe even as much as 24 hours afterwards, your innate immune system level of baseline activity is ramped up, allowing you to better combat infections such as colds and flus.

Okay, so this is an incentive for getting regular exercise of 60 minutes or less per day, making it of sufficient intensity for your innate immune system to deploy more of those chemicals and for your lymphatic and blood circulation to increase their exchange of materials enough that your innate immune system is bolstered.

However, it is absolutely not the case that more is better. In fact, it's probably the case that less is better. Here's what we know for sure. And this review covers sort of the extreme of these examples. But for instance, people that do bouts of walking each day for about 60 minutes, brisk walking, experience increased T cell function.

So that's an immune cell that goes out and combats cold and flu viruses and natural killer cell activity. So those increase. Increased macrophage function. You are now familiar with these cells. If you don't know exactly what they do, just keep in mind that you heard about these in the context of what the innate immune system does to go out and fight colds and flus.

Cytokines increase, but not dramatically, okay? So this is a mild inflammation response. Stress hormones such as cortisol, epinephrine, norepinephrine, also called adrenaline and noradrenaline. Those are deployed as well. So 60 minutes or less of this moderate to high intensity exercise creates this mild stress response and an increase in the function of the innate immune system.

However, people that run a marathon, and as I recall, a marathon is 26.2 miles, if I'm not mistaken, they experience a very different pattern of immune response to that long bout of exercise. So here we're comparing one hour of exercise to three hours. Is that what it takes to run a marathon?

I have some friends that are marathoners. I'm guessing about three, maybe four hours if you're really slow, but somewhere between, I don't know, two and a half and three hours if you're trained up and you're doing it and you're doing them regularly. Well, here's the point. People who just ran a marathon and people who have been training for a marathon and are approaching that marathon are severely immune compromised.

The levels of their T cell function are way below baseline, meaning their innate immune system is not functioning nearly as well as it would if they were to not exercise at all. Their natural killer cell activity is also greatly diminished. These are huge, huge reductions in these cells that is in the function of the innate immune system and their stress hormones and their inflammatory molecules such as cytokines circulating in their blood are extremely high.

Now again, we're representing opposite ends of the spectrum here with one hour or less of exercise daily versus 26.2 mile marathon exercise or half marathons as the case may be. And let me be very direct. I'm not discouraging people from running or training for marathons or half marathons. I think that's great.

Just understand what you're doing to your immune system when you do that and take the necessary precautions. But I think most people listening to this are trying to think about ways that they can avoid getting colds and flus. And certainly running marathons is not going to be the way to do that.

Quite the contrary. The way to do that is in addition to the other things we've been talking about to get regular exercise, maybe not every single day. I'm actually a fan of taking one day per week completely off from exercise. Usually on that day, I'll do some sauna and cold if I have it available to me.

But the point is this, you don't have to exercise for an hour a day in order to get this improvement in the innate immune response. Data show that you can get this improvement in innate immune response with as little as 20 minutes per day and probably even as little as 12 minutes per day.

However, if you're going to try and accomplish this increase in the innate immune system function or output with a shorter bout of exercise, such as 12 minutes, it better be 12 minutes of very high intensity training. In fact, that's what lands on my, for me, it's Friday, but it doesn't really matter which day of the week.

There's one day of the week where I do a very short bout of cardiovascular exercise, but I'm sprinting hard for anywhere from 20 seconds to a minute. And then I'm taking a brief period of rest and then repeating that for a total of 12 minutes. Now, some people hear, oh, only 12 minutes of exercise required.

And they default to 12 minutes every single time they train. I don't think that's a good idea. I think that we can take the law of averages here and say the following. I do believe everyone should do a combination of cardiovascular training and resistance training. Perhaps, I think in general, not on the same days, but if you're going to do that and you want to maintain healthy immune system function, my suggestion, what I do is unless it's the long bout of cardiovascular training that I do once a week and long for me means 60 to 90 minutes and sometimes longer if it's a hike, which certainly doesn't require that much intensity, I suggest warming up for about five to 10 minutes and then limiting your total workout duration to about 50 minutes, maybe 60 minutes if that's what's required to complete what you need to do in order to keep with your exercise goals.

But to be very careful about exceeding 75 minutes of exercise in any one single exercise bout. And if you remember back to the beginning of the episode, when I said that I track what I do on a day-to-day basis, and I don't do it in a very detailed way, but I do take note of when I've gotten a bad flu or cold, I can tell you that in almost every single case where I've gotten a bad flu or cold, there are two things that have proceeded that bad flu or cold.

One is sleep deprivation. Typically it would be nights where I got two hours of sleep or less for more than one night, okay? The second thing is any time that I really pushed it with exercise and went all out and I went for 75 minutes and then I continued to 90 minutes and then maybe later that day, because somebody invited me on a run or something like that, I also did that second run or that second workout of some kind, could be running in the morning and weight training in the afternoon.

Some people can do that kind of training on a regular basis even and not get sick. I am not such a person. I've managed to maintain fairly consistent fitness output, meaning the three cardiovascular and the three weight training sessions per week for more than several decades now. And part of the reason I think I've been able to do that is because I don't ever push too hard for too long within a given workout.

So this is really a call for moderation in terms of the duration and intensity of the exercise that you're doing, but we're not talking about really being laid back. We're not talking about easy workouts. What we're talking about is an hour or less of moderate intensity to high intensity exercise, depending on the duration of that exercise, and keeping in mind that when you're doing that, you are activating that innate immune system.

You're literally creating an immune response. You're increasing inflammation. You're increasing those cytokines. You're increasing stress hormones. We have to start to think about exercise for what it is, which is a form of stress that induces adaptations. Dr. Andy Galpin talked a lot about this in the series that he did on exercise physiology.

It's an excellent series that covers everything from strength to hypertrophy to speed to endurance, nutrition, supplementation. You can find all that at HubermanLab.com very easily. Exercise is a very potent tool. We know that, we know that in the context of changing aesthetics, like body mass composition, increasing muscle, reducing fat.

We know that in the context of reducing resting heart rate, reducing resting blood pressure. We know that in the context of all these other health metrics. Here, we're talking about using exercise as a very potent tool to increase the function of the innate immune system to keep you healthy, not just through the winter months, but around the year, and especially if you're getting less sleep.

If you're interacting with kids or adults that are carrying infections home from school or work on a regular basis, or maybe you even work in an environment like a hospital or a clinic where you're regularly interacting with patients that have these issues. One thing that I often get asked is, if I am sleep deprived, should I exercise?

And that's a little bit of a tricky one. My initial response for many years was, no, no. If you're sleep deprived, you're better off not exercising. However, I now need to qualify that answer because there are data showing that if you're sleep deprived and you exercise, especially if you exercise early in the day and it doesn't disrupt your sleep schedule, so it's not making you go to sleep even later the next night, that it actually can cause some adjustments in the function of your immune system and in the way that you regulate your blood sugar that offset some of the negative effects of sleep deprivation.

That said, you should never ever compromise the amount of sleep you could get in order to get exercise such that you run yourself down. So what I'm really saying here is if you get one bad night's sleep, should you skip your workout and you feel like, ah, you know, I'm not feeling sick and should I work out or should I go back to sleep?

Probably going back to sleep's the better idea, but if you don't have the option to go back to sleep for whatever reason, you can't fall back to sleep, then you would be wise to do a bout of exercise, but I would suggest reducing the intensity and duration of that exercise by about 25%, maybe even 50%.

And that should allow you to offset any of the negative effects of sleep deprivation for that one night. Keep in mind, exercise is not a replacement for sleep. And then to allow you to get to sleep at the appropriate time later that night and back onto a regular schedule, keeping your innate immune system tuned up and ready to combat any colds or flus.

Now, one more point about exercise, and here we're also going to dovetail in an important point about nutrition. In the review that I mentioned a few moments ago, they cover some of the data from studies exploring the post-exercise stress response. So this is the post-exercise induced increase in things like cortisol, those natural killer cells, the production of white blood cells, and so on.

It's very clear that if you are in a state of chronic stress because you're exercising a lot and or because you're not sleeping enough, or for whatever reason, maybe you have a lot of life stress, it's very clear that ingesting carbohydrates after exercise can help attenuate some of the inflammation that exercise induces.

When we talk about carbohydrates, we're talking about rice, oatmeal, pasta, those sorts of things, so-called complex carbohydrates. And fruit post-exercise has been shown to attenuate, to reduce some of the markers of inflammation by about 30 to 40%, when contrasted with water only intake, especially if you're training fasted. So for those of you like me that like to wake up in the morning and just drink fluids, for me, it's water, yerba mate, coffee.

And by the way, I've said before that people should delay their caffeine intake 90 minutes if and only if they're experiencing an afternoon crash, but that if you are exercising first thing in the morning, it's perfectly fine to ingest your caffeine right away. So that gives you an increase in energy for that exercise.

That's certainly what I do on days that I exercise. But if you fast and then you're drinking caffeine and then you're exercising, and that exercise goes longer than 60 minutes, certainly if it goes longer than 75 minutes, you would do well to ingest some complex carbohydrates, maybe also some fruit, perhaps not immediately after exercise, but within the 45 minutes or so or hour or so after exercise so that you're not ramping up those inflammatory molecules and leaving them ramped up for many hours into the morning and throughout the day.

Because of course this episode is not about exercise and nutrition, but here we're talking about the role that exercise and nutrition play in helping us combat colds and flus by increasing the function of that innate immune system. And the reasons why carbohydrates can have this effect on cortisol, et cetera, is an interesting and important discussion into itself.

We'll leave it for another episode, but keep that in mind. Also, I don't know about you, but a nice bowl of oatmeal, some fruit, and a protein drink or some eggs after an hour or so of exercise in the morning when I haven't eaten anything since the night before, it tastes really, really good.

So continuing with the theme of things that we can do at the level of behaviors to improve the function of our innate immune system and combat colds and flus, perhaps even prevent us from getting colds and flus at all, but certainly help combat them if they've initially made their way into our system, but we haven't developed full-blown symptoms and we want to prevent those full-blown symptoms, is the use of deliberate heat exposure, in particular, sauna.

There's a nice study on this that was published very recently, 2023. The title of the study is The Effects of a Single and Series of Finnish Sauna Sessions on the Immune System Response and Heat Shock Protein 70 Levels in Trained and Untrained Men. It's a very interesting study. They compared athletically trained and non-athletically trained men.

As most of you probably know, when you get into a hot sauna, heart rate increases, there's vasodilation, there's the increase in the release of heat shock proteins, there's the increase in things like dynorphin, which if it's sufficiently hot, are increased to levels that make us feel kind of agitated and not so good.

We have to actively calm ourselves in the sauna, so we're not talking about an easy cruise at 150 degrees Fahrenheit. We're talking about getting up into the 180 degree Fahrenheit or 210 degree Fahrenheit range, maybe even higher if you're heat adapted. And the dynorphin makes you feel lousy in the short term, but that it upregulates a bunch of different biological mechanisms that give you kind of low level euphoria and actually the capacity to experience more feelings of wellbeing from the endorphins that you make after you get out of the sauna.

This is oh so important to understand whether or not we're talking about exercise or deliberate cold exposure, deliberate heat exposure. What happens during the heat exposure, cold exposure exercise is more often than not, just the trigger for the long-term adaptation that we're seeking. Just like exercise increases your heart rate and blood pressure, but then leads to reductions in resting heart rate and blood pressure and so on and so forth.

This study is interesting and there are a lot of different takeaways from this study because they compare these two different populations. I'll just give you the top contour of what the protocol entailed. There were 10 sauna sessions. Each of those sauna sessions were three rounds of 15 minutes of sauna.

So one session meant going into the sauna. The sauna was of a given temperature, but I think for most people, what's going to work in terms of what parallels this study is going to be somewhere between 176 and 210 degrees Fahrenheit, depending on how heat adapted you are. Always be safe, don't do this if you're pregnant, don't do this if you're a child, et cetera.

So they're doing three rounds of 15 minutes each separated by two minutes. During that two minutes, they take a cool shower where they cool off in some way. They're not going into a cold plunge, but they're cooling off with a cool shower. And they're doing that three times, that's one session.

They do 10 sessions. Those sauna sessions were spaced apart by at least a few days and the entire experiment, meaning all 10 sessions were completed within a three week period. And then a bunch of things were measured, like the amount of white blood cells and immune cells that were deployed after the first session versus the third versus the eighth versus the 10th and so on, as well as the levels of cortisol and inflammatory markers.

There are a lot of different things measured in this study. Here's what we know. Sauna baths, as they're calling them, resulted in a statistically significant increase in cortisol concentration after the first and the 10th sauna session, okay? So every time you go into the sauna, you're getting an increase in cortisol.

We know that because the heat is a stressor. Again, don't think about heat as, oh, you're just kind of relaxing in the sauna, it's so nice. You're getting a cortisol response. Cortisol is a glucocorticoid stress hormone, as it's sometimes called, which can be a good thing if it sets in motion a number of other things, such as the increase in the activity of the innate immune system.

And indeed that is what they observed. After, and here I'm paraphrasing, after the first and 10th sauna baths, they witnessed an increase in leukocyte count. Leukocytes are a particular type of cell of the innate immune system. However, only after the last sauna session did this change reach statistical significance in the trained group.

So what they observed was that athletes who are trained are used to being in high heat conditions because of their athletic training. People who are not trained in athletics are not used to that. There are a lot of different ways to look at these data, but the simplest takeaway is that if you are already very heat adapted because you do sauna regularly or you exercise regularly, well then it's going to take a stronger stimulus or more sauna, either longer or hotter or more frequent to get the sorts of increases in innate immune response as compared to someone who's never done sauna, who's not exercising regularly.

And that just makes sense. If something isn't stressful to you, you're not going to get the stimulation of that innate immune response. And the overall takeaway from this study was that I do believe that if you're feeling run down a little bit or if you're just trying to keep colds and flus at bay, having some regular-ish practice of getting into the sauna for three rounds of 15 minutes separated by two minute cool off, you don't necessarily have to do a cold shower or a cold plunge in between, although I don't see why you couldn't or wouldn't, but you could also just get out of the sauna and be in the cool air and then get back in.

Or perhaps you do something more akin to what's been shown in other studies that explore the relationship between heat exposure and immune response, which is to do two rounds of 20 minutes or one round of 30 minutes in the sauna, whatever you can do safely and comfortably. Keep in mind, safety is key.

Don't harm yourself. I say that not to protect me, but to protect you. That sauna is an effective way of increasing the activity of the innate immune system. It increases leukocyte levels. Yes, it increases cortisol levels, but in a way that promote the activity of the innate immune system.

However, and here we are back to exactly the same thing we said about exercise. If you're already feeling really run down, feeling kind of heaviness in the body, you don't feel well, you're starting to get some sniffles, don't get in a very hot sauna. But for sake of keeping colds and flus at bay, sure.

Do three rounds of 15 minutes in the sauna between 176 degrees, 210 degrees, whatever you can safely tolerate. Take those two minute breaks in between, maybe do a cold shower or coolish shower, maybe just stand outside the sauna in between. If you're feeling really strong, do a cold plunge for a minute or two minutes in between.

You don't have to, but you certainly could. And then get back in and then repeat. Or just do one 20 minute session or 30 minute session, all of which have been shown to promote the activity of the innate immune system. However, and I realized I said this before, but I feel like I need to say it again, especially for you hardcore exercisers or people that really feel like, oh, I can push through.

If you're already sick and you have the symptoms of a cold or flu, you want to limit the amount of stress to your body. You want to get into bed and sleep. If you can't sleep, you want to relax. You do not want to exercise. You should not exercise.

Not only do you stand to get other people ill by going places where you exercise, but even if you exercise at home or in total isolation, you're going to prolong the duration of that illness. Because there are many, many reasons why being still, slowing your circulation, and allowing your innate, and then in that case, your adaptive immune system to kick in and combat those infections is going to get you back into a regular exercise and work regimen, much, much faster than would be the case if you were to push through.

Okay, so now we get to the portion of the discussion that I think probably many people are anticipating, which is what can you take to reduce the probability of getting a cold or flu or shorten the duration of a cold or flu? And I actually put out a call on social media.

I asked the question on Instagram and on X, formerly called Twitter, you know, what do you do for a cold or flu? And what are you curious about in terms of what one can take for cold or flu? And I got thousands upon thousands of answers. However, many of those answers converged on some common things.

Things like taking garlic. I heard, for instance, that some people are chewing a raw clove of garlic every day during the winter. I heard about people who take fermented garlic. Some people swear by echinacea. Some people swear by echinacea, vitamin C, and zinc. Now, there are far too many compounds that exist in the wellness and indeed in the medical literature to cover all of them.

So I'm going to highlight a few that I think are especially interesting and that have been shown in peer-reviewed science to be potentially useful. Some of these you've heard of before, and some of them I think are going to be surprising or at least new to you. First, let's consider what most people believe to be a very effective way to hasten colds or flus, that is to make them last shorter duration of time than they would otherwise, maybe even prevent colds or flus.

The big one there is vitamin C. We hear all the time, vitamin C, antioxidant. I grew up in an area where the Nobel prize-winning chemist, Linus Pauling, who was a fanatic about vitamin C, he took many, many grams of vitamin C each day, used to tout the benefits of vitamin C.

Here's the deal. There is some evidence, and it's not great, frankly, that points to the fact that taking six to eight grams, grams, so that's 6,000 to 8,000 milligrams of vitamin C per day. That is a lot of vitamin C. Each day can perhaps delay the onset of a cold or shorten the duration of a cold.

So here we're talking about very high doses and not a very robust effect. I should mention that for most people who aren't accustomed to taking much vitamin C, if you were to take six to eight grams of vitamin C in capsule or powder or pill form, chances are you're going to experience some significant gastric distress.

Some people can build up to that level or take it with food in a way that doesn't cause that gastric distress, but many people will experience gastric distress. There's been a lot said about vitamin C and its other potential roles in our physiology, and I don't want to touch on those now because it may have some interesting roles in other aspects of our physiology, but I have to say that in scouring the literature on vitamin C, I encountered a recent paper, so this was published in 2023, and the title of this paper is "Retraction." Extra dose of vitamin C based on a daily supplementation shortens the common cold, a meta-analysis of nine randomized controlled trials.

What is this paper that was recently published? Why is retraction the first word in the title? Well, it turns out that the meta-analysis of nine randomized controlled trials showing a small but significant improvement in the outcomes for colds and flus or reduction in probability of getting colds and flus, that study was retracted, and it was retracted on the basis of multiple instances of an error in which the placebo groups had been double-counted in trials more than the two intervention arms, so there were some serious data analysis flaws in that meta-analysis.

Now, that is not to say that vitamin C is of zero benefit for reducing the probability of colds and flus, but I must say, provided that you're getting sufficient amounts of vitamin C from your food intake, maybe you also get a little bit in your vitamin mineral supplement, or if you take a foundational supplement like AG1 or something similar, almost certainly you're getting enough vitamin C, it does not seem that taking high doses of vitamin C, and I would place six to eight grams of vitamin C in the high dose range, is going to be effective for treating or preventing colds and flus.

So more data may arrive in the near future, but vitamin C is probably not a very good investment if you're taking it solely for the purpose of enhancing your immune system function and staving off colds and flus. Now, what about vitamin D? We hear a lot these days about the importance of having sufficient vitamin D levels, and ideally everyone would get their vitamin D levels measured by regular blood tests.

I do get my blood work done every six months, I find it be incredibly informative, tells me what's going on below the hood in ways that I never could be aware of were I not to get that test, but I realized that there's a cost to those tests and not everyone can afford them.

I think most physicians would agree that supplementing with anywhere from 1,000 to 2,000 IU of vitamin D per day is probably safe for most people and will buffer that level of vitamin D in their system, such that they're unlikely to be deficient and unlikely to far exceed what's safe in the body.

However, there are people who need higher levels of vitamin D supplementation in order to achieve sufficient amounts of vitamin D for their mental health and physical health. I mean, vitamin D is involved in a lot of different processes in the brain and body. Now, it is clear that people who are vitamin D deficient, so these are people whose vitamin D levels have been measured, oftentimes have diminished immune system function and are more prone to acute respiratory tract infections.

There's a very lengthy and very interesting review entitled "Vitamin D Supplementation to Prevent Acute Respiratory Tract Infections, Systematic Review and Meta-analysis of Individual Participant Data." This is a beast of a thing. I did read it all. Very, very interesting. Many, many studies. The exact takeaways from a large review like this of 25 randomized control trials is a little bit tricky.

I mean, they did conclude that vitamin D supplementation did reduce the risk of acute respiratory tract infection among all the participants. However, the degree of prevention was small to moderate in some cases. They did point out, however, that just because people with low levels of vitamin D tend to get colds and flus more often than people that don't, does not necessarily mean that vitamin D deficiencies are the reason for that.

For instance, we know that people that get regular sunlight exposure, and as everyone knows, I'm a big, big proponent of getting sunlight in your eyes as early as possible in the day after waking up. And if it's cloudy out to get even more time outside, if you can, and if you can't get access to sunlight for whatever reason, to perhaps invest in a 10,000 lux light tablet, you can find these online at reasonable cost, you know, $100 to $200 in some cases.

Getting sunlight sets in motion a huge number of different things, including increasing the amount of vitamin D in your system, but a bunch of other things as well. Increases in cortisol, increases in dopamine, increases in serotonin that cascade toward and relate to improved immune system function. So what is the takeaway here?

I think that for most people supplementing with 1,000 to 2,000 international units of vitamin D is probably safe. However, if you need more vitamin D, you won't know that unless you take a vitamin D test, that is you measure the amount of vitamin D in your bloodstream. And some people indeed need 5,000 to 10,000 IU of vitamin D per day, but you don't want to overdose yourself on vitamin D.

That is if you already have sufficiently high levels of vitamin D in your system, you're getting sufficient sunlight, well then taking 10,000 or more international units of vitamin D could possibly be detrimental. I think it's fair to say based on the meta analysis and review that I mentioned a moment ago, the other papers that I was able to glean that vitamin D itself is unlikely to be the sole protectant against colds and flus, but it's probably a good thing to include in your general kit of nutrition and supplementation tools if your goal is to keep your innate immune system fighting off colds and flus sufficiently.

Other things that could perhaps support the innate immune system are going to be, as I mentioned earlier, the things that support the gut microbiome. So those low sugar fermented foods, maybe a prebiotic probiotic capsule, maybe something like Athletic Greens AG1, although certainly you could achieve sufficient microbiome support from foods if you're careful and intentional about the foods that you select.

Now the other compound or substance that we often hear about in the context of colds or flus is echinacea. Echinacea is a compound that has been proposed to improve immune system function. Now, when you go into the data and you explore what does taking echinacea tinctures or other forms of echinacea really do to avoid colds and flus?

The answer that comes back is not much, if anything. Now, is taking echinacea dangerous? Probably not. However, it has been shown in a few studies that people that take echinacea regularly at high doses can potentially impede the function of their innate immune system. That is reductions in white blood cell count, reductions in those natural killer cells.

So my suggestion would be, if you absolutely love echinacea for whatever reason, you're convinced that it helps you, that you reserve to taking it when you're starting to feel a little bit run down or perhaps just in the winter month, not months, plural, but month, when you're most prone to those cold and flu infections, but then not taking it continuously throughout the year and certainly not for more than four weeks at a time.

But again, if you're doing that, just know that there aren't really any strong scientific data to support the use of echinacea. By contrast, there are pretty darn good data that support supplementing with zinc as a way to combat colds and flus, in particular, colds. Now, here, the dosages really matter.

It's been shown that if you take less than 75 milligrams of zinc in supplement form to try and impact the probability of getting or shortening a common cold, it's not going to work. You need to take 100 milligrams or more. And now 100 milligrams or more of zinc, for some people, is going to cause some gastric distress if you take it on an empty stomach.

I've actually made the mistake of taking, I think it was 50 milligrams of zinc on an empty stomach, and I felt really nauseous, did not feel well. So don't take zinc on an empty stomach. And if you're trying to shorten a cold or flu that you think you've already contracted, or you're trying to keep a cold or flu at bay 'cause you were around people with colds or flus, or you're just worried about it, taking 100 milligrams of zinc, perhaps divide it up into two doses of 50 milligrams each, or maybe 100 milligrams all at once, but making sure that you take that with at least a moderately sized or full meal certainly could be advantageous.

Keep in mind that people that are older than 65 are perhaps the ones that need to supplement zinc the most. Also keep in mind that children, meaning people younger than 15, should probably not supplement with too much zinc. It can be problematic. And certainly pregnant women should talk to their doctor before supplementing with zinc.

Indeed, anytime you're going to take anything, whether or not you're young, old, pregnant or not, you should consult your physician before you take anything or remove anything from your health protocols. One of the more interesting aspects of supplementing with zinc that I was able to find in the literature is a three times faster recovery rate for people that already contracted a cold.

So in this study, people weren't taking 100 milligrams, but the dosage came pretty close. They were taking 90 milligrams per day of zinc acetate, and they experienced a three times faster recovery rate from that cold compared to people who were not taking the zinc. Now, of course, there could be other factors as well, but the study was fairly convincing.

So given that zinc is fairly low cost, given that it's generally safe for most people, and the fact that if you take it with food, it doesn't cause any discomfort, supplementing with zinc at a level of anywhere from 90 to 100 milligrams per day, probably no more than 120 per day, seems like a logical way to stave off colds and flus and reduce the duration of a cold or flu should you contract one.

Now, I want to be very clear that I've been talking about colds and flus kind of in concert, kind of treating them more or less as the same thing. Some of that is for sake of time and simplicity. Most all of the studies showing a benefit of zinc are studies showing the benefit of zinc for the treatment or the hastening of colds, not for flus specifically.

However, I consulted with a few physicians and one of whom is expert in this area, and he said, "I didn't see any reason why you wouldn't take zinc if you had a flu." There's no reason to think that it would introduce any kind of increased risk, but again, consult with your physician before taking or removing anything from your supplement regimen.

Now, a lot of the compounds that we're discussing are sort of conventional in the sense that I think most people have probably heard of them already. Perhaps the most esoteric sounding one thus far is echinacea, which we established probably not very helpful for colds or flus, but we've been talking about vitamin C, we've been talking about zinc, vitamin D, making sure you're getting your sunlight, supporting your microbiome, and so on and so on.

One compound that I'm guessing most people perhaps have not heard of, but that is very interesting that in fact I've taken before and that I stock in my supplement cabinet in case I feel like I'm coming down with something, is N-acetylcysteine or NAC. What is NAC? NAC is a precursor to glutathione.

What is glutathione? Glutathione is the master antioxidant. It's involved in reducing what are called reactive oxygen species, which build up in cells that are very metabolically active. Reactive oxygen species build up even more in cells that are under stress or a body that's under stress. And it also has the property of reducing reactive nitrogen species.

Reactive oxygen and reactive nitrogen species significantly increase under conditions of infection and having sufficient levels of glutathione is a good thing. Now, N-acetylcysteine is used in certain clinics overseas and in the US as a way to treat cystic fibrosis because it's also a mucolytic. And cystic fibrosis is the buildup of fluid in the lungs and a mucolytic substance is something that loosens up the mucus and allows it to flow more readily out of different cavities of the body, including the lungs, the nasal passages and sinuses.

And indeed last winter, I did unfortunately get a cold. I told you about once every 18 to 24 months, I get a cold and it was a pretty nasty one. I was feeling super congested. At first, I thought it was an ear infection. Pretty quickly, I realized I had a cold and I was feeling so congested, I wasn't sleeping well.

And it was suggested to me to take N-acetylcysteine. I ended up doing that at a dosage of anywhere from 600 to 900 milligrams, three times per day. So it was a 600 to 900 milligram capsule, depending on which brand I purchased. A lot of different versions of this out there on the market.

I took it morning, late morning and afternoon. And indeed it is a powerful mucolytic. The mucus just starts flowing out. You better have an extra box of tissues handy. And that greatly relieved the pressure in my sinuses. And the reason I liked using NAC is because I've actively avoided using decongestants that one can purchase over the counter.

Most decongestants are of the alpha-1 agonist variety. What's an alpha-1 agonist? It causes vasoconstriction. That vasoconstriction can be beneficial in preventing some of the intense congestion that one gets when you have a sinus infection or a cold or a flu. But then when those decongestants wear off, one tends to get a rebound increase in congestion and it's really painful, headache, et cetera.

In addition, some over the counter decongestants can be habit forming. Not necessarily addictive, but habit forming. And they don't seem to have any other positive health benefits. So I prefer not to take decongestants if I can avoid it. I had a very good experience with NAC. And the use of NAC, N-acetylcysteine, as a decongestant and also as a way to prevent getting colds and flus is not an entirely new idea.

In fact, there's a paper dating back to 1997 entitled "Attenuation of Influenza-like Symptomology "and Improvement of Cell-Mediated Immunity "with Long-Term N-acetylcysteine Treatment." Now, in this study, they looked at people who were taking 600 milligrams of N-acetylcysteine twice per day for six months. And what they observed is that the people who took N-acetylcysteine had a significantly lower probability of contracting influenza.

Now, this is but one study. There've been a few other studies and unfortunately there isn't a large body of research looking at NAC as a preventive for colds and flus. But the data in this paper are interesting enough and I was compelled by them enough to seek out a physician who I noticed was answering my prompts on social media about what do you use for colds and flus?

And when I put that out there, as I mentioned, I got thousands of responses on both Twitter X and on Instagram. And one particular physician who happens to have a YouTube account, his name is Dr. Schwelt. He's a medical doctor. He works in an intensive care unit and he deals with a lot of patients who have different strains of flu.

In fact, he was the one that cued me to the fact that this year, there seems to be a fair number of H1N1 flu virus going around. And remember the H1N1 flu virus, while it's not deadly to everyone, it can be quite severe in some people. So we do want to be on the lookout for and trying to avoid getting H1N1 if we can.

I spoke to Dr. Schwelt. He was very generous with his knowledge about N-acetylcysteine. He did acknowledge, and I'll acknowledge again here, that it would be great to get more randomized control trial data on N-acetylcysteine. But we did talk about this paper, this 1997 paper. And he did mention that he and other clinicians that are forced to be in the hospital dealing with patients all through the winter and all year long, they're getting bombarded with cold and flu exposure all the time, that they, meaning he and some of his colleagues, deliberately take N-acetylcysteine as a preventative to try and reduce the probability of getting colds and flus.

And while we don't want to make too much of any one study or anecdotal data, which is what we're describing when I tell you about a physician who told me this or what I did and experienced that, I think it is worth paraphrasing the study that I mentioned before.

NAC prevented the symptomatic forms caused by, here they're talking about the A, H1N1 influenza virus quite efficiently. Since the large majority of infected subjects in the placebo group, 79%, developed clinically apparent disease versus only 25% in the NAT group. In other words, approximately 80% of people in the study who did not take N-acetylcysteine got influenza, whereas only 25% of the people who were taking N-acetylcysteine contracted influenza.

So that's a fairly dramatic difference. And certainly the fact that N-acetylcysteine has been shown to increase glutathione, that's its primary mechanism of action as far as we know, and the fact that increases in glutathione are generally healthy and good for us, and the fact that N-acetylcysteine is still available legally over the counter in the US, at least currently it is, some years back, as you may have heard, the FDA called for removal of N-acetylcysteine from over the counter sales.

That I should point out was based on the fact that certain supplement companies were making claims about N-acetylcysteine as a treatment for hangover and making a bunch of other claims for which there was no real data, but either because the FDA was effective in getting those companies to cease those claims and/or because of advocacy groups, which worked very hard to try and keep N-acetylcysteine available for over the counter sales.

As far as I know, at least right up until prior to recording this episode, N-acetylcysteine is available for sale over the counter. So whether or not you decide to use N-acetylcysteine as a preventative, and there again, the dosage is about 1200 milligrams per day divided into two different dosages of 600 milligrams each, or if you decide to take N-acetylcysteine in the manner that I did, which was not as a preventative, but once I had a cold, couldn't fight it off, apparently got the cold, decided to take 900 milligrams three times per day, avoiding that intake close to sleep because it did disrupt my sleep if I took it too close to sleep because of the way that the mucus would flow so readily.

You know, essentially, I know it sounds gross, but I felt like it was filling up the back of my throat, so-called post-nasal drip, but it felt like post-nasal waterfall. And I decided to restrict my intake of N-acetylcysteine to earlier in the day only. And of course, there's the third option, which is that you opt to not take N-acetylcysteine until more randomized control trials are published, or not take N-acetylcysteine at all because you're of the sort that thinks, okay, with some sleep, a hot shower, a good meal, some chicken soup, maybe a little garlic, who knows?

Maybe you have some other tools and techniques that you like, you like that ginger tea, lemon, et cetera. Maybe that's all you need. And if that's all you need and that's all you want in order to deal with a cold or flu, be my guest. I certainly am not here to convince anyone that you have to take a certain supplement, but I did feel like I would be remiss if I didn't cover what are generally referred to as the so-called preventatives and treatments for colds and flus, things like zinc, vitamin D, vitamin C.

We now know that unfortunately, vitamin C gets a, probably a D- or an F at least as the data stand now, but there are these other things like zinc and potentially N-acetylcysteine that can be beneficial in shortening the duration of colds or flus and perhaps even helping us avoid getting colds or flus all together.

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