AMA #7: Cold Exposure, Maximizing REM Sleep & My Next Scientific Studies

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

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

00:00:04.900 | for everyday life.

00:00:05.900 | I'm Andrew Huberman, and I'm a professor of neurobiology

00:00:12.260 | and ophthalmology at Stanford School of Medicine.

00:00:15.340 | Today is an Ask Me Anything episode or AMA.

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00:01:42.600 | Without further ado, let's get to answering your questions.

00:01:45.780 | The first question asks,

00:01:47.200 | is it possible to get a cold or to get sick

00:01:49.500 | from deliberate cold exposure?

00:01:51.180 | And I suppose a related question is,

00:01:52.820 | should you even do deliberate cold exposure

00:01:55.380 | if you have a sniffle, a cold, or a flu?

00:01:58.460 | I get that question all the time as well.

00:01:59.860 | So I'll answer both of those questions.

00:02:01.740 | And I will also touch on some of the immune enhancing effects

00:02:05.300 | of deliberate cold exposure.

00:02:07.060 | But just to make sure that we answer the specific question

00:02:09.700 | asked here right off the bat,

00:02:11.400 | is it possible to get a cold or to get sick

00:02:14.160 | from deliberate cold exposure?

00:02:16.320 | Well, assuming that you're not doing

00:02:17.700 | the deliberate cold exposure

00:02:19.460 | for more than say five or six minutes at one stretch,

00:02:24.700 | probably not directly from the deliberate cold exposure.

00:02:29.000 | I mentioned that because most people are doing

00:02:30.780 | anywhere from about a minute to three minutes,

00:02:33.060 | sometimes five or six minutes,

00:02:34.420 | and maybe for those of you that are really pushing it,

00:02:36.580 | 10 minutes of deliberate cold exposure.

00:02:38.980 | And most often after doing that deliberate cold exposure,

00:02:41.820 | people are either getting clothed

00:02:43.600 | or they're getting into a sauna

00:02:44.800 | or they're taking a hot shower and then getting clothed

00:02:47.740 | and heading off into their day or off to sleep,

00:02:50.180 | depending on what time of day or night

00:02:51.540 | you happen to do your deliberate cold exposure.

00:02:54.760 | We can safely say that if you warm up

00:02:56.580 | after a relatively brief, meaning one minute to,

00:02:59.260 | let's extend it out to 10 minutes,

00:03:01.100 | 10 minute deliberate cold exposure,

00:03:02.780 | although I really want to caution people

00:03:04.100 | to not do 10 minute deliberate cold exposure

00:03:06.100 | right off the bat.

00:03:07.020 | If you are somebody who is not accustomed to it,

00:03:09.220 | don't jump right up to that long exposure to cold water,

00:03:13.940 | start with shorter exposures.

00:03:16.120 | But if you're doing that one to 10 minute

00:03:17.900 | deliberate cold exposure,

00:03:19.220 | and then you're getting warm afterwards

00:03:20.820 | and heading about your day,

00:03:22.140 | I can't see how the deliberate cold exposure itself

00:03:25.060 | would enhance your susceptibility to getting sick.

00:03:29.740 | That said, we know from an enormous number of studies

00:03:33.280 | that have looked at cold virus transmission

00:03:35.540 | and other forms of viral and bacterial transmission,

00:03:39.060 | that the environment that you happen to be in

00:03:41.860 | does impact your susceptibility to colds

00:03:44.980 | and other types of viruses and to bacterial infections

00:03:48.460 | in the following way.

00:03:50.140 | There have been controlled studies in which people

00:03:52.420 | go into laboratories.

00:03:54.380 | Those laboratories have rooms

00:03:56.260 | in which they can very tightly control the humidity,

00:03:59.420 | so essentially the water content in the air,

00:04:01.660 | as well as the temperature in the room.

00:04:04.240 | And if you look at the total mass of those data,

00:04:07.200 | we can say a couple of specific things

00:04:09.660 | in kind of bullet point fashion.

00:04:11.140 | First off, cold, dry air does seem to increase

00:04:15.580 | our susceptibility to viral and bacterial infections

00:04:19.020 | because whether or not you're a mouth breather

00:04:21.360 | or a nose breather,

00:04:22.260 | and by the way, I suggest everyone be a nose breather

00:04:24.620 | unless you're exercising hard enough

00:04:26.500 | that you have to breathe through your mouth

00:04:27.660 | or you're talking or something of that sort.

00:04:30.020 | But if you're a nose breather or a mouth breather or both,

00:04:33.020 | viruses and bacteria enter through your nose and mouth,

00:04:38.100 | sometimes through your eyes,

00:04:39.280 | but your nose and mouth are going to be

00:04:41.020 | the main sites of entry and your main barriers

00:04:43.620 | to viral and bacterial infections.

00:04:45.180 | In fact, one of the ways you are constantly fighting off

00:04:48.120 | bacterial and viral infections

00:04:49.580 | that you're exposed to all the time

00:04:51.920 | is by way of those viruses and bacteria getting trapped

00:04:55.620 | in the mucus lining of your nose or your mouth,

00:04:59.020 | most notably in the back of your throat.

00:05:01.320 | So if you spend time in cold, dry environments,

00:05:05.100 | there is a tendency for that mucosal lining to be thinner.

00:05:08.100 | There is a tendency for that mucosal lining

00:05:10.400 | to not be as robust in general.

00:05:12.860 | When I say robust, what I mean is that

00:05:14.500 | if you're mouth breathing, for instance,

00:05:16.180 | in a cold, dry environment,

00:05:17.860 | I'm thinking from the time I spent

00:05:19.620 | in Cambridge, Massachusetts in winter at the tea station,

00:05:23.140 | you know, if you're, I'm just imagining myself

00:05:24.940 | 'cause it was so darn cold back there,

00:05:26.600 | you know, breathing through your mouth

00:05:28.580 | or having gone for a run and your mouth isn't covered,

00:05:32.200 | or even if you're deliberately nasal breathing,

00:05:34.440 | you are drying out your nasal passages

00:05:36.260 | and making them more susceptible to infections.

00:05:39.680 | Does that necessarily mean that

00:05:41.160 | every time you go out in cold, dry air

00:05:43.120 | that you're going to get an infection?

00:05:44.500 | No, of course it doesn't.

00:05:45.980 | But to relate this back to the question we had before,

00:05:49.260 | there are a lot of data pointing to the fact

00:05:51.020 | that more humid, warm environments

00:05:54.000 | are going to make your mucosal lining

00:05:56.260 | and the general upper respiratory area more,

00:06:00.300 | I don't want to say immune

00:06:01.280 | 'cause I don't want to conflate that word

00:06:02.700 | with the other meaning of immune,

00:06:03.940 | it's going to make it more robust

00:06:06.020 | against bacterial and viral infections, okay?

00:06:09.860 | So if you get into a cold shower or a cold plunge

00:06:14.820 | or a cold ocean or a cold lake,

00:06:17.140 | and then you get out and you're out there,

00:06:18.740 | you know, shivering and shaking,

00:06:19.820 | trying to boost your metabolism,

00:06:21.780 | whatever it is that you're doing it for,

00:06:24.360 | and it's cold, dry air,

00:06:26.340 | and especially if you're mouth breathing

00:06:27.740 | in that cold, dry air,

00:06:29.220 | yes, I could see how that might lead

00:06:31.460 | to a higher probability of getting a cold

00:06:34.420 | or other type of infection.

00:06:35.840 | But there's nothing specific

00:06:37.420 | about the deliberate cold exposure itself

00:06:40.500 | that can induce a cold or other type of infection,

00:06:43.980 | assuming that the water is clean, right?

00:06:45.700 | We're not talking about bacterial infections

00:06:47.220 | of cuts on the skin, et cetera.

00:06:48.680 | We're talking about colds and other forms of being sick,

00:06:52.020 | namely upper respiratory infections, okay?

00:06:54.660 | Now, with that said, I often get asked

00:06:57.900 | whether or not for people who already have a little sniffle,

00:07:01.180 | they're feeling a little rundown,

00:07:02.980 | or perhaps a lot rundown,

00:07:04.140 | should they do deliberate cold exposure?

00:07:06.660 | It's a little tricky to give a one-size-fits-all answer,

00:07:10.660 | but I think we can safely say

00:07:12.820 | that if you are feeling malaise,

00:07:14.920 | if you're feeling like you have to rest,

00:07:16.540 | you're tired, you're not feeling good because of a cold

00:07:20.900 | or because of a flu or because of a bacterial infection,

00:07:24.220 | okay, now I'm not saying just feeling not good,

00:07:26.760 | I'm saying feeling not good due to a cold

00:07:30.040 | or other form of virus or bacterial infection,

00:07:32.460 | then I would say stay out of deliberate cold exposure.

00:07:34.980 | Don't use it.

00:07:36.380 | Now, why would I say that?

00:07:37.300 | Given the data I'll talk about in a few minutes,

00:07:39.240 | showing that regular deliberate cold exposure,

00:07:42.260 | if done correctly, can in fact increase immune system markers

00:07:46.580 | and perhaps even to make you much more robust

00:07:49.180 | to combating different types of infection

00:07:50.980 | through the release of adrenaline.

00:07:52.440 | We'll talk about what all that looks like in a moment

00:07:54.700 | in terms of protocols and some of the science,

00:07:56.540 | but to just be very clear and very direct,

00:08:00.060 | if you're sick, stay out of deliberate cold exposure.

00:08:03.140 | There, I would instead recommend warmer hot baths,

00:08:06.280 | warmer hot showers, the sauna, et cetera,

00:08:09.300 | but I also would caution that if you are getting

00:08:12.580 | into saunas that are too hot,

00:08:14.380 | saunas that are so hot that it's stressful for you,

00:08:17.180 | and again, a lot of people use deliberate heat exposure

00:08:19.220 | because of the stress it induces.

00:08:20.680 | They're doing some heat-induced,

00:08:22.980 | for instance, heat shock proteins

00:08:24.880 | and different ways of increasing heart rate.

00:08:26.940 | That's a different sort of thing.

00:08:28.540 | That's hard, stressful in order to generate an adaptation.

00:08:33.140 | I don't recommend doing that.

00:08:34.760 | In fact, I don't recommend doing deliberate cold exposure,

00:08:37.460 | exercise or deliberate heat exposure

00:08:39.020 | if you're feeling really not well.

00:08:41.900 | Now, if you're feeling just a little bit not well,

00:08:43.920 | you're feeling a little bit rundown,

00:08:45.260 | a little bit of sniffle, a little bit of malaise,

00:08:48.500 | well, then it's kind of an edge case

00:08:50.180 | where we could say, all right, you know what?

00:08:52.040 | Just take a hot shower and go to sleep.

00:08:53.740 | That's probably the best advice, right?

00:08:55.660 | That good old-fashioned advice.

00:08:57.540 | But if you are determined to do

00:08:59.340 | your deliberate cold exposure anyway,

00:09:02.020 | then I would say definitely get warm

00:09:03.700 | or take a hot shower afterwards, hot bath or a hot sauna,

00:09:07.100 | but not too hot that it's stressful, of course.

00:09:09.580 | And keep in mind that one of the variables

00:09:11.080 | that's been measured quite a lot in laboratory studies

00:09:13.460 | of deliberate cold exposure

00:09:14.940 | is the increase in immune system markers.

00:09:16.980 | So I'll provide a few links to some of these studies,

00:09:20.140 | although nowadays there are many, many of them,

00:09:23.380 | but it's very clear that deliberate cold exposure

00:09:27.140 | can increase the release and the production

00:09:31.520 | of different immune molecules and immune cells.

00:09:34.260 | One slightly older study, but nonetheless,

00:09:37.100 | a good study that has relevance here

00:09:38.940 | is entitled "Immune System of Cold Exposed

00:09:41.120 | and Cold Adapted Humans."

00:09:43.300 | Keep in mind that this study is a little bit extreme,

00:09:46.400 | and there are reasons for that,

00:09:48.140 | I guess to make a long story short.

00:09:50.340 | Oftentimes in order to "see an effect" in a study,

00:09:53.740 | scientists will use conditions that are pretty extreme

00:09:57.300 | compared to control group.

00:09:58.880 | Oftentimes you'll see a dose response too,

00:10:00.620 | but it's a little bit trickier to do

00:10:02.160 | with human studies of deliberate cold exposure.

00:10:04.600 | It can be done, but not too common.

00:10:06.020 | But here they used a pretty,

00:10:07.640 | what I would call extreme stimulus.

00:10:09.260 | It was exposing people to 14 degrees Celsius water.

00:10:13.000 | So that's 57.2 degrees Fahrenheit, which isn't that cold.

00:10:17.120 | It's kind of like cool, I would say very cool water,

00:10:19.880 | but not what you might consider cold,

00:10:21.860 | depending on how well you tolerate cold,

00:10:23.520 | and that will vary of course.

00:10:24.920 | But they had people exposed to that for an hour,

00:10:27.740 | which is a pretty long time.

00:10:29.640 | Most people, as I mentioned, are using colder temperatures

00:10:32.380 | of deliberate cold exposure.

00:10:33.420 | So even, you know, high 30s, low 40s,

00:10:37.280 | maybe upper 40s for anywhere from one to 10 minutes,

00:10:40.300 | depending on how conditioned they are.

00:10:42.540 | And again, don't just jump into 10 minutes

00:10:45.020 | of deliberate cold exposure,

00:10:46.180 | please at, you know, 35 degrees or 40 degrees

00:10:49.700 | or even 45 degrees.

00:10:50.820 | If you aren't familiar with deliberate cold exposure,

00:10:52.780 | you have to ease into these sorts of things over time.

00:10:55.140 | And if you're interested in protocols

00:10:56.640 | for deliberate cold exposure,

00:10:57.640 | we have a zero cost newsletter at hubermanlab.com,

00:11:00.580 | go to the menu, go newsletter, and you can find that.

00:11:02.860 | We've done several episodes on deliberate cold exposure.

00:11:06.340 | In any event, this study,

00:11:08.620 | Immune System of Cold Exposing Cold Adapted Humans,

00:11:11.000 | as I mentioned, had people in 14 degrees Celsius water

00:11:13.920 | for one hour.

00:11:15.140 | And basically what they found is that one exposure to cold

00:11:17.960 | did not change immune system function

00:11:20.020 | in any kind of significant way.

00:11:21.900 | However, what they found was

00:11:24.220 | if people did deliberate cold exposure repeatedly

00:11:26.760 | over a period of about six weeks,

00:11:29.100 | and by repeatedly, I mean three times per week,

00:11:32.060 | what they found were trends.

00:11:33.980 | And again, trends are not statistically significant,

00:11:37.200 | but trends towards increases in plasma concentrations

00:11:40.820 | of things like IL-6, interleukin-6,

00:11:43.200 | or total numbers of T lymphocytes and T helper cells

00:11:46.180 | and T suppressor cells and activated T and B lymphocytes.

00:11:49.720 | These are all immune cells and immune molecules

00:11:52.900 | that roughly correspond to an increase

00:11:55.620 | in immune system function.

00:11:56.660 | If you'd like to learn more about the immune system,

00:11:58.240 | I did an episode on immune system function.

00:12:00.160 | Again, you can find that at hubermanlab.com,

00:12:02.020 | and it spells out the basic cell types

00:12:03.900 | of what's called the innate and the adaptive immune system.

00:12:06.740 | This study, which we will link to in the show note captions,

00:12:08.900 | is but one study of several other studies showing

00:12:11.980 | that deliberate cold exposure

00:12:13.100 | can increase immune system markers,

00:12:14.600 | especially when deliberate cold exposure

00:12:16.660 | is done repeatedly over time.

00:12:18.460 | So in this case, three times a week

00:12:19.700 | over a period of six weeks.

00:12:21.100 | But again, I want to highlight,

00:12:22.240 | these aren't highly significant effects.

00:12:23.860 | These are trends in the direction

00:12:25.660 | of increased numbers of immune cells and immune markers.

00:12:28.440 | Now, what's impossible to know

00:12:30.500 | is how those trends translate to actual resistance

00:12:34.820 | to specific concentrations of say cold virus or flu virus

00:12:37.940 | or any other virus or bacteria.

00:12:39.720 | That would be great,

00:12:40.560 | but that's a very difficult study to do,

00:12:42.540 | especially in the context

00:12:43.580 | of deliberate cold exposure as well.

00:12:45.500 | Now, we can all be scientists about this and say,

00:12:49.440 | what is it about deliberate cold exposure

00:12:51.180 | that would increase immune system function?

00:12:54.140 | And there, we can confidently say

00:12:56.260 | the molecules epinephrine and norepinephrine,

00:12:58.740 | which are released in both brain and body

00:13:00.780 | in response to cold water exposure,

00:13:03.340 | as well as things like deliberate hyperventilation.

00:13:07.060 | The release of norepinephrine and epinephrine

00:13:08.980 | into the brain and body is known

00:13:10.900 | to have a number of different effects

00:13:12.840 | related to the immune system.

00:13:14.220 | It can be pro-immune, at least in the short term,

00:13:17.980 | and in the long term,

00:13:19.580 | meaning if noradrenaline and adrenaline,

00:13:22.120 | again, those are just different names

00:13:23.420 | for norepinephrine and epinephrine.

00:13:24.900 | I'm sorry, those are the same thing,

00:13:26.040 | but that's why I use them interchangeably

00:13:27.860 | so that you don't get confused.

00:13:28.920 | If you see noradrenaline or norepinephrine,

00:13:31.960 | that's the same thing.

00:13:32.800 | You hear epinephrine or adrenaline, same thing.

00:13:35.300 | Deliberate cold exposure or deliberate hyperventilation

00:13:38.700 | will increase those molecules,

00:13:41.540 | norepinephrine and epinephrine,

00:13:43.420 | and their increase is pro-immune.

00:13:46.500 | It can trigger the activation of immune cells

00:13:50.100 | and immune molecules that can make you more resistant

00:13:53.020 | to certain forms of infection.

00:13:54.840 | However, if norepinephrine and epinephrine

00:13:57.020 | are elevated chronically,

00:13:59.080 | and especially if they are elevated late in the day,

00:14:02.160 | repeatedly over many, many days,

00:14:04.340 | that can cause reductions in the number and efficiency

00:14:08.360 | of immune cells in combating infections.

00:14:10.740 | So getting cold in this context of whether or not

00:14:13.260 | you can get sick from it should really be considered more

00:14:15.560 | as what happens when you spike your adrenaline

00:14:17.900 | and norepinephrine.

00:14:19.580 | And there's one other study that we can look to,

00:14:21.820 | which is now really a famous study published

00:14:23.900 | in "Proceedings of the National Academy of Sciences"

00:14:26.180 | looking at so-called Wim Hof breathing,

00:14:28.540 | but really that just translates

00:14:29.980 | to cyclic hyperventilation.

00:14:31.700 | So this is inhaling through the nose,

00:14:33.180 | exhaling through the mouth repeatedly 25 times or so.

00:14:35.900 | [inhaling and exhaling]

00:14:38.980 | If you do that, you notice you feel quite warm.

00:14:41.220 | Has to do with some things related to vasodilation,

00:14:43.900 | has some things to do with release

00:14:45.420 | of norepinephrine and epinephrine.

00:14:46.620 | We know that pattern of deliberate hyperventilation,

00:14:48.780 | much like deliberate cold exposure,

00:14:51.000 | deploys or releases noradrenaline and adrenaline

00:14:54.160 | into your brain and body.

00:14:55.440 | And we know from this study entitled "Voluntary Activation

00:14:58.260 | "of the Sympathetic Nervous System

00:14:59.460 | "and Attenuation of the Nate Immune Response in Humans"

00:15:02.460 | showed really nicely, I think,

00:15:04.620 | that if people are injected with E. coli, right, a bacteria,

00:15:09.620 | it's actually, they did this through endotoxin injections,

00:15:12.560 | people got really sick.

00:15:13.940 | They'd get, you know, feel like they had the flu,

00:15:16.220 | they vomit, diarrhea, get a fever, et cetera.

00:15:19.140 | However, if they did the sorts of breathing

00:15:21.120 | that I talked about just a moment ago,

00:15:23.880 | prior to that, they were able to ward off

00:15:26.260 | a lot of the symptoms associated

00:15:29.240 | with the endotoxin infection.

00:15:31.040 | And you would say, okay, wow,

00:15:32.160 | their immune system just fired up

00:15:33.640 | and they were able to fight it off.

00:15:34.940 | But it's trickier than that, actually.

00:15:36.500 | What happened was the release of epinephrine

00:15:38.980 | and norepinephrine from cyclic hyperventilation,

00:15:41.680 | which is really what [inhaling and exhaling]

00:15:43.800 | really is cyclic hyperventilation,

00:15:46.380 | also called Wim Hof breathing,

00:15:47.500 | also called Tummo breathing, et cetera,

00:15:49.820 | that actually had a suppressive action

00:15:52.340 | on certain arms of the immune system

00:15:55.560 | in a way that allowed people to avoid symptomology,

00:15:59.080 | such as fever, nausea, et cetera.

00:16:02.140 | And we would imagine the same thing would occur

00:16:04.080 | with deliberate cold exposure

00:16:06.180 | done prior to bacterial infection or viral exposure.

00:16:10.620 | So if you're sensing that I'm saying two things at once,

00:16:13.580 | I am.

00:16:14.500 | I'm saying deliberate cold exposure

00:16:16.220 | and cyclic hyperventilation can both cause deployment

00:16:19.200 | of molecules such as epinephrine and norepinephrine

00:16:23.420 | that lead to enhanced immune system function

00:16:25.220 | if done repeatedly.

00:16:26.420 | I'm also saying that increasing norepinephrine

00:16:29.020 | and epinephrine too much can suppress your immune system.

00:16:33.640 | In this study, the PNAS study that I mentioned a moment ago,

00:16:36.420 | that suppression of the immune response

00:16:38.020 | was actually one of the reasons people avoided symptomology,

00:16:40.700 | but they were still injected with endotoxin,

00:16:42.780 | so they just weren't fighting off the endotoxin with fever.

00:16:45.100 | Remember, fever is an adaptation to fight infection.

00:16:48.300 | It's designed essentially to heat up the infection

00:16:51.120 | and kill it.

00:16:52.140 | So what are we to take away from this?

00:16:54.660 | Here are what I think are the key takeaways.

00:16:57.500 | One, if you are feeling good to great,

00:17:00.620 | do your deliberate cold exposure.

00:17:02.340 | And perhaps don't worry so much

00:17:03.860 | about using your body's natural metabolism

00:17:06.780 | and thermogenic abilities to heat back up afterwards.

00:17:10.580 | But I don't suggest anyone ever allow themselves

00:17:13.540 | to stay really cold after deliberate cold exposure

00:17:17.060 | for more than 10, 15 minutes or maybe half an hour, right?

00:17:20.580 | Get bundled back up or put on clothes.

00:17:22.500 | If it's a nice hot sunny day,

00:17:23.880 | get out in the sun and warm up.

00:17:25.640 | Again, temperatures and conditions will vary

00:17:27.800 | for different people, different locations, et cetera.

00:17:30.460 | If you are not feeling great,

00:17:33.460 | you're feeling a little rundown

00:17:34.720 | and you really want to do your deliberate cold exposure,

00:17:37.140 | do it, but then warm up really well afterwards.

00:17:39.700 | Maybe even drink some hot tea

00:17:41.260 | or other fluid afterwards as well.

00:17:44.040 | And if you are not feeling good,

00:17:45.740 | you're feeling malaise, you're feeling rundown,

00:17:48.740 | despite what you read about deliberate cold exposure

00:17:52.580 | or cyclic hyperventilation,

00:17:54.440 | allowing for the deployment of immune molecules

00:17:57.200 | or increasing the number of immune cells that you're making,

00:18:00.460 | avoid anything that's stressful or challenging,

00:18:04.900 | whether or not it's a cold challenge, a heat challenge,

00:18:07.740 | or an exercise challenge when you're feeling rundown,

00:18:09.960 | because under those conditions,

00:18:11.180 | what you really want to do is slow your circulation down,

00:18:13.940 | probably find it take little walks or something,

00:18:15.660 | provided you're not doubled over in bed

00:18:17.200 | and vomiting and things like that.

00:18:18.980 | A little bit of movement,

00:18:19.860 | probably good to circulate your blood.

00:18:21.700 | But in general, the advice that you get to rest

00:18:24.460 | when you're sick and not push yourself,

00:18:27.220 | that's really good advice

00:18:28.420 | because you want all of your body's resources to be devoted

00:18:31.920 | to getting over that infection.

00:18:33.980 | And if you're interested in sickness and sickness behavior

00:18:37.160 | and the sorts of behaviors that can combat infection,

00:18:39.580 | check out the episode I did on the immune system.

00:18:41.580 | We'll link to it in the show note captions

00:18:43.020 | because it talks about how when we have a viral

00:18:44.940 | or bacterial infection,

00:18:46.620 | a whole set of brain circuits get activated

00:18:48.920 | that kind of encourage us to be more in the fetal position,

00:18:52.160 | to move less, to be eyes down, to kind of slump down.

00:18:55.900 | That's not a coincidence.

00:18:57.580 | That's because of the activation

00:18:58.960 | of these so-called sickness circuits

00:19:00.660 | that are really designed to help you heal yourself.

00:19:03.140 | So I both apologize and what do the kids say?

00:19:06.960 | Sorry, not sorry.

00:19:08.080 | Don't apologize for the somewhat nuanced answer here

00:19:12.500 | because a lot of information out there says,

00:19:14.340 | "Oh, you know, cold boosts your immune system."

00:19:16.660 | And yeah, that's true under certain conditions.

00:19:18.540 | It can also deplete your immune system

00:19:20.960 | and limit your ability to fight off infections

00:19:23.320 | under other conditions.

00:19:24.900 | And perhaps the last thing to say about this

00:19:27.280 | is that I am a big believer in using nasal breathing

00:19:30.940 | whenever you don't have to breathe through your mouth.

00:19:33.480 | So if you're exercising hard,

00:19:34.640 | by all means, breathe through your mouth.

00:19:36.000 | If you're doing martial arts

00:19:36.900 | and it requires that you breathe through your mouth,

00:19:38.940 | go ahead and do that.

00:19:40.140 | But if you're doing say zone two cardio, low level cardio,

00:19:43.160 | or you're just walking along,

00:19:44.180 | it's very clear based on a growing amount of data

00:19:46.780 | that being a nasal breather

00:19:47.760 | is better than being a mouth breather.

00:19:49.220 | And there are a number of different reasons for that.

00:19:50.820 | We've talked about on the podcast and elsewhere,

00:19:53.080 | but one of the additional reasons is

00:19:55.760 | a main site of entry for infections is through the mouth.

00:19:58.780 | So keep that mouth shut unless you need to talk.

00:20:02.080 | Thank you for joining

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AMA #7: Cold Exposure, Maximizing REM Sleep & My Next Scientific Studies

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