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

ANDREW HUBERMAN: Welcome to the Huberman Lab podcast

where we discuss science and science-based tools

for everyday life.

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I'm Andrew Huberman, and I'm a professor

of neurobiology and ophthalmology

at Stanford School of Medicine.

Today is an ask me anything episode, or AMA.

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Without further ado, let's get to answering your questions.

The first question asks, is it possible to get a cold

or to get sick from deliberate cold exposure?

And I suppose a related question is, should you even

do deliberate, cold exposure if you have

a sniffle, a cold, or a flu?

I get that question all the time as well.

So answer both of those questions.

And I will also touch on some of the immune enhancing effects

of deliberate cold exposure.

But just to make sure that we answer

the specific question asked here right off the bat,

is it possible to get a cold or to get sick from deliberate

cold exposure?

Well, assuming that you're not doing

the deliberate cold exposure for more than,

say five or six minutes at one stretch,

probably not directly from the deliberate cold exposure.

I mention that because most people

are doing anywhere from about a minute

to three minutes, sometimes five or six minutes.

And maybe for those of you that are really

pushing it, 10 minutes of deliberate cold exposure.

And most often after doing that deliberate cold exposure,

people are either getting clothed,

or they're getting into a sauna, or they're taking a hot shower,

and then getting clothed and heading off into their day

or off to sleep depending on what time of day or night

you happen to do your deliberate cold exposure.

We can safely say that if you warm up

after a relatively brief, meaning one minute to,

let's extend out to 10 minutes, 10-minute deliberate

cold exposure, although, I really

want to caution people to not do 10-minute deliberate

cold exposure right off the bat.

If you are somebody who is not accustomed to it,

don't jump right up to that long exposure to cold water.

Start with shorter exposures.

But if you're doing that one-to-10-minute deliberate,

cold exposure, and then you're getting warm afterwards

and heading about your day, I can't see how the deliberate

cold exposure itself would enhance your susceptibility

to getting sick.

That said, we know from an enormous number

of studies that have looked at cold virus transmission

and other forms of viral and bacterial transmission

that the environment that you happen to be in

does impact your susceptibility to colds

and other types of viruses and to bacterial infections

in the following way.

There have been controlled studies in which people

go into laboratories.

Those laboratories have rooms, which they can very tightly

control the humidity, so essentially,

the water content in the air, as well

as the temperature in the room.

And if you look at the total mass of those data,

we can say a couple of specific things

in kind of bullet point fashion.

First off, cold, dry air does seem

to increase our susceptibility to

viral and bacterial infections.

Because whether or not you're a mouth breather or a nose

breather, and by the way, I suggest everyone be a nose

breather unless you're exercising hard enough that you

have to breathe through your mouth,

or you're talking or something of that sort.

But if you're a nose breather or a mouth breather or both,

viruses and bacteria enter through your nose and mouth,

sometimes through your eyes, but your nose and mouth

are going to be the main sites of entry

and your main barriers to viral and bacterial infections.

In fact, one of the ways you are constantly fighting off

bacterial and viral infections that you're

exposed to all the time is by way

of those viruses and bacteria getting

trapped in the mucous lining of your nose

or your mouth, most notably in the back of your throat.

So if you spend time in cold, dry environments,

there is a tendency for that mucosal lining to be thinner.

There is a tendency for that mucosal lining

to not be as robust in general.

And when I say robust, what I mean

is that if your mouth breathing, for instance

in a cold, dry environment, I'm thinking from the time

I spent in Cambridge, Massachusetts in winter

at the T station.

If you're I'm just imagining myself

because it was so darn cold back there breathing

through your mouth or having gone for a run,

and your mouth isn't covered, or even if you're deliberately

nasal breathing, you are drying out your nasal passages

and making them more susceptible to infections.

Does that necessarily mean that every time you

go out in cold, dry air that you're

going to get an infection?

No, of course it doesn't.

But to relate this back to the question we have before,

there are a lot of data pointing to the fact that more humid,

warm environments are going to make your mucosal lining

and the general upper respiratory area more,

I don't want to say immune because I

don't want to conflate that word with the other meaning

of immune.

It's going to make it more robust against

bacterial and viral infections.

So if you get into a cold shower or a cold plunge

or a cold ocean or a cold lake, and then you get out,

and you're out there shivering and shaking, trying

to boost your metabolism or whatever

it is that you're doing it for, and it's

cold, dry air, and especially if your mouth

breathing in that cold, dry air, yes, I

could see how that might lead to a higher

probability of getting a cold or other type of infection.

But there's nothing specific about the deliberate, cold

exposure itself that can induce a cold or other type

of infection assuming that the water is clean, right?

We're not talking about bacterial infections

of cuts on the skin, et cetera.

We're talking about colds and other forms of being sick,

namely upper respiratory infections.

OK, now with that said, I often get asked whether or not

for people who already have a little sniffle,

they're feeling a little run down or perhaps a lot run down,

should they do deliberate cold exposure?

And what's a little tricky to give a one size fits all

answer, , but I think we can safely say that if you are

feeling malaise, if you're feeling like you have to rest

you're tired, you're not feeling good because of a cold

or because of a flu or because of a bacterial infection, now,

I'm not saying just feeling not good,

I'm saying feeling not good due to a cold or other form

of virus or bacterial infection, then I would say stay out

of deliberate, cold exposure.

Don't use it.

Now, why would I say that?

Given the data I'll talk about in a few minutes showing

that regular deliberate cold exposure if done correctly,

can in fact increase immune system markers

and perhaps even make you much more robust to combating

different types of infection through the release

of adrenaline.

We'll talk about what all that looks like

in a moment in terms of protocols

and some of the science.

But to just be very clear and very direct, if you're sick,

stay out of deliberate cold exposure.

There, I, would instead recommend

warmer hot baths warmer hot showers, the sauna, et cetera.

But I also would caution that if you are getting into saunas

that are too hot, saunas they're so

hot that it's stressful for you, and again, a lot of people

use deliberate heat exposure because of the stress

it induces, they're doing some heat induced,

for instance, heat shock proteins and different ways

of increasing heart rate.

That's a different sort of thing.

That's hard, stressful in order to generate an adaptation.

I don't recommend doing that.

In fact, I don't recommend doing deliberate cold exposure,

exercise, or deliberate heat exposure if you're

feeling really not well.

Now, if you're feeling just a little bit not well,

you're feeling a little bit rundown, a little bit

of sniffle, a little bit of malaise, well then,

it's kind of an edge case where we could

say, all right you know what?

Just take a hot shower and go to sleep.

That's probably the best advice, that good old-fashioned advice.

But if you are determined to do your deliberate cold exposure

anyway, then I would say definitely get warm

or take a hot shower afterwards, hot bath, or hot sauna,

but, not too hot that it's stressful, of course.

And keep in mind that one of the variables that's

been measured quite a lot in laboratory

studies of deliberate cold exposure

is the increase in immune system markers.

So I'll provide a few links to some of these studies.

Although, nowadays there are many, many of them.

But it's very clear that deliberate cold exposure

can increase the release and the production

of different immune molecules and immune cells.

One slightly older study, but nonetheless a good study

that has relevance here is entitled

"Immune system of cold exposed and cold adapted humans."

Keep in mind that this study is a little bit extreme.

And there are reasons for that.

I guess to make a long story short, oftentimes,

in order to quote unquote "see an effect in a study,"

scientists will use conditions that are pretty extreme

compared to control group.

Oftentimes, you'll see a dose response to,

but it's a little bit trickier to do with human studies

of deliberate, cold exposure.

It can be done, but not too common.

But here, they used a pretty what

I would call extreme stimulus.

It was exposing people to 14 degrees Celsius water,

so that's 57.2 degrees Fahrenheit,

which isn't that cold.

It's like cool, I would say very cool water,

but not what you might consider cold depending

on how well you tolerate cold.

And that will vary, of course.

But they had people exposed to that for an hour, which

is a pretty long time.

Most people, as I mentioned, are using colder temperatures

of deliberate cold exposure, so even high 30s,

low 40s, maybe upper 40s for anywhere

from one to 10 minutes, depending

on how conditioned they are.

And again, don't just jump into 10 minutes of deliberate, cold

exposure, please at 35 degrees or 40 degrees

or even 45 degrees if you aren't familiar with deliberate cold

exposure.

You have to ease into these sorts of things over time.

And if you're interested in protocols

for deliberate cold exposure, we have a zero-cost newsletter

at hubermanlab.com.

Go to the Menu, go to Newsletter,

and you can find that.

We've done several episodes on deliberate cold exposure.

In any event, this study, "Immune system of cold exposing

cold adapted humans," as I mentioned,

had people in 14 degrees Celsius water for one hour.

And basically what they found is that one exposure to cold

did not change immune system function

in any kind of significant way.

However, what they found was if people did deliver

cold exposure repeatedly over a period of about six weeks,

and by repeatedly, I mean three times per week, what they found

were trends.

And again, trends are not statistically significant,

but trends towards increases in plasma concentrations of things

like IL 6, interleukin 6 or total numbers of T lymphocytes

and T helper cells and T suppressor cells

and activated T and B lymphocytes,

these are all immune cells and immune molecules

that roughly correspond to an increase in immune system

function.

If you'd like to learn more about the immune system,

I did an episode on immune system function.

Again, you can find that at hubermanlab.com.

And it spells out the basic cell types

of what's called the innate and the adaptive immune system.

This study, which we will link to in the show note captions

is but one study of several other studies showing

that deliberate cold exposure can increase immune system

markers, especially when deliberate cold exposure is

done repeatedly over time, so in this case, three times

a week over a period of six weeks.

But again, I want to highlight these aren't

highly significant effects.

These are trends in the direction

of increased numbers of immune cells and immune markers.

Now, what's impossible to know is

how those trends translate to actual resistance

to specific concentrations of, say cold virus or flu virus

or any other virus or bacteria.

That would be great, but that's a very difficult study

to do, especially in the context of deliberate cold exposure

as well.

Now, we can all be scientists about this and say, what is it

about deliberate cold exposure that would increase

immune system function?

And there, we can confidently say the molecules

epinephrine and norepinephrine, which

are released in both brain and body in response to cold water

exposure, as well as things like deliberate hyperventilation,

the release of norepinephrine and epinephrine into the brain

and body is known to have a number of different effects

related to the immune system.

It can be pro-immune, at least in the short term.

And in the long term, meaning if noradrenaline and adrenaline,

again those are just different names for norepinephrine

and epinephrine.

I'm sorry, those are the same thing,

but that's why I use them interchangeably so

that you don't get confused.

If you see noradrenaline or norepinephrine,

that's the same thing you hear, epinephrine or adrenaline,

same thing.

Deliberate cold exposure or deliberate hyperventilation

will increase those molecules, norepinephrine and epinephrine.

And their increase is pro-immune.

It can trigger the activation of immune cells

and immune molecules that can make

you more resistant to certain forms of infection.

However, if norepinephrine and epinephrine

are elevated chronically, and especially

if they are elevated late in the day repeatedly

over many, many days, that can cause reductions

in the number and efficiency of immune cells

in combating infections.

So getting cold in this context of

whether or not you can get sick from it

should really be considered more as

what happens when you spike your adrenaline and norepinephrine?

And there's one other study that we can look to,

which is now really a famous study published in proceedings

of the National Academy of Sciences

looking at so-called Wim Hof breathing.

But really, that just translates to cyclic hyperventilation.

So this is inhaling through nose,

exhaling through the mouth repeatedly 25 times or so.

[BREATHING]

If you do that, you notice you feel quite warm,

lots to do with some things relate to vasodilation,

has some things to do with release of norepinephrine.

And epinephrine, we know that pattern

of deliberate hyperventilation, much like deliberate

cold exposure, deploys or releases

noradrenaline and adrenaline into your brain and body.

And we know from this study entitled

"Voluntary activation of the sympathetic nervous system

and attenuation of the innate immune response in humans"

showed really nicely, I think.

That if people are injected with E. coli, a bacteria

it's actually an end-- they did this

through endotoxin injections.

People got really sick.

They'd get feel like they had the flu,

they vomit, diarrhea, get a fever, et cetera.

However if they did the sorts of breathing

that I talked about just a moment ago, prior to that,

they were able to ward off a lot of the symptoms associated

with the endotoxin infection.

And you would say, OK wow, their immune system just fired up,

and they were able to fight it off.

But it's trickier than that, actually.

What happened was the release of epinephrine

and norepinephrine from cyclic hyperventilation, which

is really what [BREATHING] really

is, cyclic hyperventilation, also called Wim Hof breathing,

also called tummo breathing, et cetera, that actually had

a suppressive action on certain arms of the immune system

in a way that allowed people to avoid symptomology

such as fever, nausea, et cetera.

And we would imagine the same thing would

occur with deliberate cold exposure done

prior to bacterial infection or viral exposure.

So if you're sensing that I'm saying two things at once,

I am.

I'm saying deliberate cold exposure,

and cyclic hyperventilation can both cause deployment

of molecules such as epinephrine and norepinephrine

that lead to enhanced immune system

function if done repeatedly.

I'm also saying that increasing norepinephrine and epinephrine

too much can suppress your immune system.

In this study, the PNAS study that I mentioned a moment ago,

that suppression of the immune response

was actually one of the reasons people avoided symptomology.

But they were still injected with endotoxin,

so they just weren't fighting off the endotoxin with fever.

Remember, fever is an adaptation to fight infection.

It's designed essentially to heat up the infection

and kill it.

So what are we to take away from this?

Here are what I think are the key takeaways.

One, if you are feeling good to great,

do your deliberate cold exposure.

And perhaps don't worry so much about using your body's

natural metabolism and thermogenic abilities

to heat back up afterwards.

But I don't suggest anyone ever allow themselves

to stay really cold after deliberate

cold exposure for more than 10, 15 minutes or maybe

half an hour, right?

Get bundled back up, or put on clothes.

If it's a nice hot, sunny day, get out in the sun and warm up.

Again, temperatures and conditions

will vary for different people, different locations, et cetera.

If you are not feeling great, you're

feeling a little rundown, and you really

want to do your deliberate cold exposure,

do it, but then warm up really well afterwards.

Maybe even drink some hot tea or other fluid afterwards as well.

And if you are not feeling good, you're feeling malaise,

you're feeling run down.

Despite what you read about deliberate,

cold exposure or cyclic hyperventilation,

allowing for the deployment of immune molecules

or increasing the number of immune cells

that you're making, avoid anything

that's stressful or challenging whether or not

it's a cold challenge, a heat challenge, or an exercise

challenge when you're feeling run down.

Because under those conditions, what you really want to do

is slow your circulation down, probably

find and take a little walks or something

provided you're not doubled over in bed and vomiting,

and things like that.

A little bit of movement, probably

good to circulate your blood.

But in general, the advice that you

get to rest when you're sick and not push yourself,

that's really good advice because you

want all of your body's resources

to be devoted to getting over that infection.

And if you're interested in sickness and sickness

behavior and the sorts of behaviors

that can combat infection, check out the episode

I did on the immune system.

We'll link to it in the show note captions.

Because it talks about how when we

have a viral or bacterial infection,

a whole set of brain circuits get

activated that encourage us to be more in the fetal position,

to move less, to be eyes down, to kind of slump down.

That's not a coincidence.

That's because of the activation of these so-called sickness

circuits that are really designed

to help you heal yourself.

So I both apologize, and what do the kids say?

Sorry, not sorry.

Don't apologize for the somewhat nuanced answer here.

Because a lot of information out there says,

oh, cold boosts your immune system.

And yeah, that's true under certain conditions.

It can also deplete your immune system

and limit your ability to fight off infections

under other conditions.

And perhaps the last thing to say about this

is that I am a big believer in using nasal breathing whenever

you don't have to breathe through your mouth.

So if you're exercising hard, by all means breathe

through your mouth.

If you're doing martial arts, and it

requires that you breathe through your mouth,

go ahead and do that.

But if you're doing, say a zone two cardio, low level

cardio, or you're just walking along,

it's very clear based on a growing amount of data

that being a nasal breather is better

than being a mouth breather.

And there are a number of different reasons

for that we've talked about on the podcast and elsewhere.

But one of the additional reasons is a main site of entry

for infections is through the mouth.

So keep that mouth shut unless you need to talk.

Thank you for joining for the beginning of this

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