Welcome to Huberman Lab Essentials,

where we revisit past episodes for the

most potent and actionable science-based

tools for mental health, physical

health, and performance.

I'm Andrew Huberman and I'm a professor

of neurobiology and opthalmology at

Stanford School of Medicine. Today we

are talking about the science of heat.

Heat is a remarkable stimulus, meaning

when we are in a hot environment, it has

a profound effect on our biology. So

we're going to talk about the science of

heat and heating both in terms of their

mechanisms and as I know many of you are

interested in the tools related to the

use of heat things like sauna, how often

to do sauna, how long to be in the

sauna, how hot to be in the sauna for

particular goals and outcomes. We heat

up two ways. We heat up from the

outside, meaning the things that we come

into contact with, the clothing that we

put on our body, whether or not there's

heat in the room or whether or not it's

cold outside or cold in a room. And we

heat up from the inside. At every point

across your entire lifespan, you have

two distinct temperatures. One is the

temperature on your skin, what

scientists call your shell, and the

temperature of your core, your viscera,

meaning your organs, your nervous

system, and your spinal cord. It is

vitally important to understand that you

have those two temperatures, and that

your brain is constantly sending out

signals to your body as to whether or

not it should heat up or cool down

depending on the temperature of the

shell. So, anytime we're talking about

heat, meaning deliberate heat exposure,

things like sauna, it's very important

to understand not just the stimulus, how

hot something is, how long you're in a

sauna, etc., but the effect that has on

your shell and on your core. If you can

understand that, you can design

protocols that are literally perfect for

your goals. A brief warning now and

another brief warning later. Anytime

you're talking about heating up your

body, you need to be very cautious

because unlike cooling down where you

have a fairly broad range of cold

temperatures that you can go into before

it's damaging to tissue, well, you don't

get to heat up the brain and body very

much before you start getting into the

realm of neuron damage. And neurons in

the central nervous system, the brain

and spinal cord, once they're damaged,

they don't come back. So, hypothermia is

a serious thing to avoid. There's a very

basic circuit, meaning neurons that

exist in the skin, in the brain, and in

the body that communicate with one

another that allow you to heat up if you

need to and cool down if you need to.

Once you understand this circuit and the

way it's structured, then you are going

to be in a great position to use the

tools related to heating. So, here's how

this circuit is structured. You have

this shell, which is basically skin. And

within the skin, you have neurons, nerve

cells. Those nerve cells have channels

or receptors on them. They're called

trip channels. There are some other ones

as well, which basically sense changes

in heat. So, if I were to put a hot

object on your hand or your arm, or for

instance, if I were to put a hot object

on your hand or arm and then remove that

hot object, those neurons would respond

to that. They would send electrical

signals into your spinal cord. And

that's where the next station of the

circuit resides. In your spinal cord,

you've got a little cluster of neurons

that exists at the top part of your

spinal cord called the dorsal horn. The

name again doesn't matter. And those

neurons specifically relay heat

information up to another area of your

brain. Now, here's where we get into

some fancy names. It's the lateral

parabrachial area. You don't need to

know lateral parrachial area, but it's a

relay station. The lateral parabra area

sends electrical signals to the POA. And

I would like you to know POA. The POA

stands for preoptic area. Neurons in the

preoptic area basically reside over the

roof of your mouth. These are neurons

within the hypothalamus.

And neurons in the preoptic area have

the ability to send signals out to the

rest of your brain and body to get you

to heat up and actually to change your

behavior. So there all these different

mechanisms by which we dump heat. Some

of those are purely physiological

below our conscious control. Things like

sweating, which you can't just make

yourself sweat on demand. Maybe you can

through a set of stressful thoughts, but

you can't just make yourself sweat. That

is autonomic. It's below your conscious

control. Things like vasoddilation, the

dilation of your veins in particular and

capillaries in particular. And of course

there are these behavioral somewhat

voluntary aspects of dumping heat and

the lethargy the kind of tiredness that

we feel on a really hot day that's also

controlled by this circuit that I just

described. The impulse to get yourself

out of a very hot environment is the

consequence of the POA communicating

with your amydala and the amydala then

in turn activating your adrenal glands

which are sit right above your kidneys.

the release of adrenaline and this

feeling of agitation like you want to

move. Usually you want to move out of

whatever hot environment you happen to

be in. So now you know the circuit.

Again, it's simple. It goes from skin to

spinal cord, one brain area to another

brain area. That's the key one in this

discussion, which is the POA, the

preoptic area. If you can conceptualize

that circuit or if you can even just

understand what I just said even at a

top contour level, you're going to be in

a great position to understand the rest

of the information and the tools that

follow. The use of deliberate heat

exposure can be a very powerful way to

improve health and longevity. There's a

wonderful study on this that was

published in 2018 that includes a lot of

data from a lot of participants in a lot

of different conditions. For instance,

people that only did sauna once versus

two to three times a week versus four to

seven times a week and so on and

compares all those. The title of the

study is sauna bathing is associated

with reduced cardiovascular mortality

and improves risk prediction in men and

women, a prospective cohort study. This

is one of several papers that clearly

demonstrate that regular use of sauna or

other forms of deliberate heat exposure

can reduce mortality to cardiovascular

events, but also to other events, things

like stroke and other things that

basically can kill us. What I like so

much about this and the related studies

is that they involve a lot of

participants. So for instance, in this

particular paper which was published in

BMC medicine, they looked at a sample of

1,688

participants who had a mean age of 63,

but there was a range of ages around 63

and of whom 51.4% were women, the rest

were men. So it's a pretty nicely varied

study in terms of the populations that

they looked at. Basically, what they

found was the more often that people do

sauna, the better their health is and

the lower the likelihood they will die

from some sort of cardiovascular event.

Now, what do we mean by sauna? We need

to define some of the parameters around

sauna. And I promise to provide you some

alternative ways to access some of the

health benefits that were observed in

this and related studies without the

need to have a sauna because I do

realize that a lot of people don't have

access to sauna. First off, the

temperature ranges that were used in

this study and pretty much all the

studies that I'm going to talk about,

unless I say otherwise, are between 80

degrees Celsius, meaning 176° F, and

100° C, meaning 212°

F. So, somewhere in that range. How hot

should you make the sauna or the

environment that you get into should you

decide to use these tools? Well, that

will depend on your tolerance for heat.

How heat adapted you are. Yes, some

people are better at sweating than

others. And over time, we all get better

at sweating. Meaning, if you go into the

sauna more frequently, you become a

better sweater. Not a sweater you wear,

but the verb sweater. You get better at

sweating, at dumping heat through the

loss of water. So, it's going to depend.

I recommend starting on the lower end of

the temperature scale. And if that's too

hot for you, that you even lower the

temperature further. Now, how long were

people exposing themselves to these hot

environments? Anywhere from 5 to 20

minutes per session. In this particular

study, they compared the effects of

people that did sauna once a week, two

or three times per week, or four to

seven times per week. What they observed

was that people who went into the sauna

two or three times per week were 27%

less likely to die of a cardiovascular

event than people that went into the

sauna just once a week. And today we're

mainly going to talk about exposures

between 10 and 20 minutes at

temperatures between again 80° and 100°

C, 176° Fahrenheit or 212° F. And in

fact, the benefits were even greater for

people that were going into the sauna 4

to seven times per week. Those people

were 50% less likely to die of a

cardiovascular event compared to people

that went into the sauna just once a

week. What's particularly nice about

this study and the related study is that

they looked at a number of potentially

confounding variables. Things like

whether or not people smoked, things

like whether or not people were

overweight, whether or not they tended

to exercise or not exercise, and they

were able to separate out those

variables. So the percentages that I

described earlier, those effects really

do seem to be the consequence of the

sauna exposure and not some other effect

that's correlated with sauna exposure

like going to the gym where people are

working out seven times a week and then

also happen to get into the sauna or

quitting smoking right about the same

time they adopt a a sauna protocol.

these sorts of things. And now there

have been additional analyses of the use

of sauna for improving health or I

should say for offsetting mortality that

have found that it's not just reductions

in cardiovascular events but so-called

all cause mortality. This is kind of

medical geek speak. We're saying how

likely are you or somebody to die from a

cardiovascular event but maybe also from

some other event, some other health

rellated event like cancer or something

of that sort. And in every case, regular

exposure to sauna starting at about two

or three times per week all the way up

to seven times per weekly improves,

meaning statistically significant

improvements in longevity in the sense

that they people are less likely to die

of cardiovascular events and other

things that kill us. You don't have to

use a sauna in order to get these

benefits. It is simply a matter of

making sure that your shell and your

core heat up properly. Not too much, not

too little, but that you heat those up.

So, the question is, how are you heating

up your environment? And I realize that

there are dry saunas, there are steam

saunas, there are infrared sauna, there

are hot tubs, and there are simply rooms

that you crank up the heat. Okay? There

are also ways in which you can increase

your shell and your core temperature by

moving around a lot and doing that

wearing a lot of clothing.

There's nothing special about any one of

these approaches or protocols. It just

so happens that sauna is one of the more

convenient ways to do this. And

certainly for the studies that I've

talked about, not just the ones I

referenced before, but all the studies

that I researched looking at this

episode, it makes sense why they would

use sauna because it's very hard, for

instance, to create conditions where if

you have, you know, five people go out

jogging, wearing heavy sweaters and

hats, wool hats on the middle of summer.

It's very hard to set up those

conditions in a way that's controlled

for everybody. Whereas, it's pretty

straightforward to have a sauna where

you have one or several people just get

into that one uniformly hot environment.

That's a much easier study to run. You

could, however, immerse yourself in a

hot tub or hot water bath up to your

neck. That's another way to approach it.

If you didn't have access to either of

those, you could also

put on a a hoodie or a wool hat and a

hoodie. Or you could do like the

wrestlers do. And you could actually buy

one of these uh plastic suits. They're

literally called plastics that uh

wrestlers or other athletes that wish to

drop water weight will wear and then go

jogging in that. All of those will

increase your shell and your core body

temperature, right? Especially if you do

it on a hot day. But of course, be

careful, hydrate, and don't overheat.

Don't become excessively hypothermic

because you can get heat stroke and you

can potentially die. So, what happens

when you get into a hot environment?

What are the mechanisms that allow for

the various health effects of that? So,

blood flow increases, plasma volume of

your blood increases, and stroke volume,

the volume of blood that is mobilized

with each beat of your heart also

increases. and your heart rate increases

to anywhere between 100 to 150 beats per

minute. That general constellation of

effects looks a lot like cardiovascular

exercise. And in fact, for all intents

and purposes, it really is

cardiovascular exercise except that

there isn't the mobilization and the

loading of joints and limbs and things

of that sort. And of course there are

additional benefits of cardiovascular

exercise that relate to impact on the

ground, improvements in bone density etc

etc. But basically your heart starts

beating more blood starts circulating

your vasculature changes shape literally

to accommodate those increases in heart

rate and blood volume and you're

basically getting a cardiovascular

workout in that hot environment even if

you're just sitting down. Another set of

positive effects related to being in

these hot environments

are hormone effects. Shifts in the

output of hormones both from your

adrenals and possibly from the testes

and ovaries and even within the brain.

One of the more striking examples of

that comes from a study that was

published in 2021. The title of the

study is endocrine effects of repeated

hot thermal stress and cold water

immersion in young adult men. And

indeed, the study was in this case just

done on men. I'll just briefly describe

the protocol they used. They had these

men attend four sauna sessions of 12

minutes each. So again, well within that

range of 5 to 20 minutes, 12 minutes.

The temperature of those saunas was 90

to 91° C. That's 194° Fahrenheit. And

they did that four times. Afterwards,

they had a six-minute cool down break

during which they did get into some cool

water or cold water of about 10°, which

is 10 degrees C is 50° F. And then they

measured hormones at various times

throughout this study, before, during,

and after. The major effect of this

study is a significant decrease in

cortisol output in these subjects.

I think this is really interesting and

important because many people suffer

from acute, meaning immediate and

long-term stress and are looking for

ways to control their stress.

Controlling your cortisol is tricky.

Many people are overworked. They're

overstressed for one reason or another.

They're subjected to many too many

stressors or their level of stress

resilience isn't high enough to keep

their cortisol levels clamped at a

healthy level. So the protocol I

described of 12minute exposures to

90°ree environment that's again 90° C

followed by a 6 minute cool down break

in cool water 50° or so that's pretty

cold I can imagine that you could also

just take a cool shower or a cold shower

afterwards that had a very significant

effect on lowering cortisol so there you

have a tool it's not a completely

zero-cost tool because you need to heat

the water you need to have access to hot

and cold water at least hot and cold

contrast of some sort, but it's fairly

minimal cost for most people. Especially

if you start getting creative about

maybe taking a 12-minute jog, wearing a

lot of clothing if it's hot out, then

getting into a cool shower. You might

not get the same extreme or significant

reduction in cortisol that was observed

here with these very specific protocols,

but it's likely that you would get a

similar result overall. So, if you're

seeking to use sauna to reduce stress, I

think this is a very interesting and

potentially useful researchbacked

protocol. And again, we will provide a

link to the paper uh if you'd like to

read more about the data. One of the

more dramatic and important effects of

going into a hot environment for some

period of time is the activation of

so-called heat shock proteins or HSPS.

Heat shock proteins are a protective

mechanism in your brain and body to

rescue proteins that would otherwise

misfold. What do I mean by this? Well,

most of you are familiar with the fact

that if you have protein in the kitchen,

like a steak or a piece of chicken or a

piece of fish, and you heat it up, it

changes its texture, right? Raw meat is

different than cooked meat. Heat changes

the quality of proteins, not just in

terms of how they taste, but the way in

which they are configured. Changes it

right down at the molecular level. When

your body goes through changes in

temperature in response to hot

environments or cold environments, heat

shock proteins are deployed to go and

rescue and prevent the changes in

proteins that would be detrimental to

your health. So at least in the short

term, activating heat shock proteins is

a good thing. You don't want heat shock

proteins to be activated for long

periods of time because that gets to be

problematic for other reasons. But these

heat shock proteins, of which there are

many varieties, basically have the job

of traveling in your brain and body and

making sure that cells that contain

proteins that are misfolding because

they got heated up too much don't

misfold and they also serve a protective

mechanism making sure that proteins

within the cells of your brain and body

don't fold in the wrong ways. Um, again,

I'm describing this in very general

terms, but it's well established in

animal models and in humans that sauna

exposure of the sort that I described

earlier activates these heat shock

proteins. There have been interesting

studies done in humans examining some of

the downstream molecular pathways of

deliberate heat exposure that point to

the mechanisms by which deliberate heat

exposure can help protect against

different forms of mortality, improve

health overall and possibly and I want

to highlight possibly possibly extend

life.

One such mechanism involves a genetic

program involving a molecule called FOX

03. Fox3 is a very interesting molecule

because it's involved in DNA repair

pathways. DNA repair is part of the

process of remaining healthy. You know,

we'd all like to think that we're born

and based on the genes we have, we are

healthy, healthy, healthy. Then

eventually we age and then we die. But

from the time we're born until the time

we die, there's a constant repair of our

proteins and our cells and a

modification of the genes that are being

expressed. You know, puberty being the

most dramatic example, right? You see a

kid before puberty and after puberty

looks like a different kid, sounds like

a different kid, thinks like a different

kid. In fact, basically is a different

human being, right? It's not just the

hormones, it's that hormones themselves

have the capacity to turn on and turn

off certain genes, literally converting

certain tissues and cells in the brain

and body to do entirely different

things. And DNA, the stuff of genes,

gets damaged in that process. Fox3

sits upstream in a pathway related to

DNA repair and again clearing of these

senent cells. Sauna exposure

in particular sauna exposure two to

three times or ideally four to seven

times per week in that 80 to 100 degree

Celsius range has been shown to

upregulate levels of FOX3.

FOX3 in turn upregulates pathways

related to DNA repair and clearing out

of these senocent or dead cells which is

known to be important for various

aspects of maintaining cognition and

other aspects of maintaining health. So

these are the likely biological

mechanisms for the improvements in

lifespan or I rather I should say these

are the biological mechanisms that

apparently offset some of the

cardiovascular risk and other forms of

mortality that were described earlier.

One especially interesting thing about

FOX3,

there are individuals out there that

have either additional copies of FOX3 or

who have versions of FOX3 that are

hyperactive,

so to speak. Those people tend to be 2.7

times more likely to live to 100 years

of age or longer. So these are people

that were just naturally and fortunately

for them endowed with more FOX3, more

clearance of senocin cells, more DNA

repair etc. Deliberate heat exposure is

one way that you can increase FOX3

activity. There is no sauna protocol

designed specifically to reduce cortisol

or specifically to increase FOX3 or

specifically to activate heat shock

proteins. Any deliberate heat exposure

is likely to impact all of those

mechanisms. Again, I encourage you to

use this guide of 80 to 100° Celsius as

your kind of uh bookends for what you

can tolerate and where you want to start

and eventually transition to in terms of

deliberate heat exposure. And I would

encourage you to use that 5 to 20

minutes per session for the sauna as

your rough guide of how long to remain

in the sauna. Now, I'd like to talk

about the use of sauna to increase

growth hormone. Growth hormone impacts

metabolism and growth of cells and

tissues of the body. It is responsible

for tissue repair as well. And the

growth spurt that everyone experiences

during puberty is the consequence of

growth hormone. What I'm about to

describe is a study that found dramatic

really dramatic I should say increases

in growth hormone. But I also want to

emphasize that these increases in growth

hormone were not of the sort that are

observed in puberty or in infants

becoming adolescence or adolescence

growing into teenagers. Those levels of

growth hormone that are associated with

those massive transformations, excuse

me, of body morphology of shape are far

greater than the sorts that I'm talking

about here. And yet, as all of us age,

when we go from adolescence to our

teenage years and then into young

adulthood, but then starting in our

early 30s or so, the amount of growth

hormone that we secrete is greatly

diminished.

Normally, we would release growth

hormone every night after we go to

sleep, in particular, in the early part

of the night when our sleep is comprised

mostly of slowwave sleep. As we age,

less growth hormone is released during

that slowwave sleep. Certain forms of

deliberate heat exposure using sauna can

stimulate very large increases in growth

hormone output which for people in their

30s, 40s and beyond could be very useful

and may also be useful for people who

are just trying to stimulate the release

of more growth hormone in order to for

instance recover from exercise or

stimulate fat loss or muscle growth or

repair of a particular injury. The title

of this paper is endocrine effects of

repeated sauna bathing. And this is a

paper that was published in 1986, which

is some years ago, but nonetheless

serves as a basis for a lot of other

studies that followed. They used an 80°

C environment. So that's 176 degrees

Fahrenheit. They had subjects do this

sauna for 30 minutes four times per day.

So that's 2 hours total in one day. 30

minutes in the sauna, a period of cool

down rest, 30 minutes in the sauna,

again, cool down, rest a third and a

fourth time. Okay, so two hours total in

this 80° C environment. So that's a lot,

but what they observed was really quite

significant. And I should mention they

had both male and female subjects in

this study. And the entire study lasted

a week. They did this two hours of sauna

exposure on day one, day three, and day

seven of that week. And they measured a

lot of different hormones. I'll just cut

to the chase and tell you the effects on

growth hormone in subjects that did this

2hour a day 80°ree Celsius protocol

experienced 16fold increases in growth

hormone. So they measured growth hormone

before the sauna and after the sauna and

growth hormone levels went up 16fold

which is obviously an enormous and it

turns out statistically significant

effect. One important caveat here.

Remember earlier when I talked about

people who did sauna once a week versus

two to three times a week versus four to

seven times a week. And the more often

people did sauna, the less likely they

were to die of cardiovascular events or

other things of that sort. Well, in this

case, the effects of sauna exposure on

growth hormone actually went down the

more often that people did this

deliberate heat exposure. So, as I

mentioned, they did this 2-hour a day

divide into 30-minute sessions protocol

on day one, day three, and day seven of

a week. And what they found was on day

one, there was a 16-fold increase in

growth hormone. On day three, however,

there was still a significant effect on

growth hormone as compared to before

sauna, but that effect was basically cut

by 2/3. Okay? So now instead of getting

a 16-fold increase, it was more like a

three or four-fold increase, which is

still a huge increase, but not as great

as the increase observed on day one. And

then on day seven, there tended to be a

two maybe a three-fold increase, but not

as great as the one observed on day one.

The fact that that result diminished

over time either means that the circuit

was not as efficient in communicating

that shift in temperature or that that

shift in temperature was of less impact

because the downstream aectors were not

engaged to the same extent because it

wasn't as much of a shock. And I think

the latter explanation is far more

likely. This is very much akin to weight

training or cardiovascular exercise

where if you run up a hill very fast for

instance and your lungs are burning and

you're heaving and breathing hard on the

first day that's a very painful thing.

But if you do it every day or every

other day provide you allow yourself to

recover pretty soon you're running up

that hill and you're not breathing as

hard. There isn't much burning in your

muscles etc etc. Your body adapts. So,

if you're going to use deliberate heat

exposure in order to try and trigger

massive increases in growth hormone,

you're going to need to be careful about

not doing it more than, let's say, once

a week. Now, I'm extrapolating from this

study, maybe once every 10 days would be

even better. But if you start getting

heat adapted, it's very unlikely that

you're going to get these massive

increases in growth hormone. So, I don't

mean to be discouraging of using

deliberate heat exposure to access

growth hormone increases, but if that's

your specific goal or your main goal,

then I think it's reasonable to say that

you don't want to do deliberate heat

exposure, at least not of the sort that

I described here, more than once a week

or maybe even once every 10 days. and

that you would want to time that to

other events in your life, maybe hard

workouts or if you're trying to push

through a fat loss barrier or simply in

order to access growth hormone at peak

levels, maybe three times per month or

four times per month. If you start doing

deliberate heat exposure more often,

you'll still get increases in growth

hormone, but they are not going to be

nearly as large as the increases in

growth hormone that you're going to

experience if you shock your system with

deliber deliberate heat exposure every

once in a while. When you decide to do

sauna or cold exposure for that matter

is going to be important. Why? Well, if

you were to make the surface of your

body cold, at least in the immediate

period after that, your body temperature

will increase and that can make it hard

for some people to fall asleep. Now, if

you're very very tired because you've

been working hard or training hard or

both throughout the day, it might not

throw off your sleep so much. I've gone

through bouts where I'm just so so busy

from morning till night that the only

time I can get into the ice bath or the

cold shower is late in the evening and I

have no trouble sleeping after that. If

you're going to use deliberate heat

exposure, you'd be wise to do it later

in the day because when you get into a

warm environment, sure, the surface of

your body, the shell heats up, the core

of your body heats up, but then it also

activates cooling mechanisms through the

preoptic area, and when you get out of

that hot environment, sauna, otherwise,

your body will continue to cool down.

And so many people find that if they do

sauna in the later half of the day or

even just before sleep and then take a

warmest shower afterwards, then they

find it easier to fall asleep. And that

makes sense because their body

temperature is dropping. And in fact, if

your goal is to really promote the

maximum amount of growth hormone

release, that's also going to be the

best time of day to do it, especially if

you haven't eaten in the two hours

before sleep. Okay? Okay, so if you're

really going for growth hormone release,

you're really trying to optimize sleep.

And the two things are actually linked

because of the release of growth hormone

that happens from the pituitary in the

early night sleep, well then you would

be wise to do your sauna maybe once or

maybe twice a week in the evening or at

night time. Then taking a warm or cool

shower, just briefly, just enough to

kind of rinse off all the sweat from the

sauna and then get ready for sleep. And

to do that, not necessarily fasted, but

to try and keep your levels of glucose

and insulin somewhat low in your

bloodstream. The reason I say that is

that having elevated blood glucose and

or insulin tends to blunt or reduce

growth hormone release. And that's true

for any number of different stimuli,

including exercise and including sauna.

If you really want to crank out the most

amount of growth hormone in response to

sauna, do it fasted or at least not

having ingested any food in the two or

three hours before. You don't have to be

deep into a fast. I think for 90% of

people, 90% of the time, just getting

into the sauna once or twice or three

times a week is going to be beneficial

for the number of reasons that I

described earlier. And you don't want to

obsess too much about the exact

conditions you need in order to get the

greatest effect out of that sauna

treatment. Now, regardless of what time

of day you do sauna or how frequently

you do it, you're going to want to

hydrate after going in the sauna. When

you go in the sauna, you lose water. And

when you lose water, you need to replace

it. Why? Well, you need water for all

your cells, but you also need

electrolytes. So, make sure that you're

replacing the water that you lose in the

sauna. Now, there's no exact formula of

how much water to drink and whether or

not you need electrolytes in that water

or not. It's going to depend on how much

you sweat, meaning how heat adapted you

are. It's going to depend on how much

salt you tend to excrete in your sweat.

Huge amount of variation. But in

general, one way to approach this would

be to make sure that you drink at least

16 ounces of water for every 10 minutes

that you happen to be in the sauna. You

could do that before and during and

after. You could do it during and after

or you could do it after. Now, there are

other reasons to do deliberate heat

exposure that have improvements in mood

and mental health. In fact, the data

related to sauna and other forms of

deliberate heat exposure improving mood

are very impressive both at the

mechanistic level and in terms of the

long-term consequences that people

experience. First of all, we need to

ask, how is it that deliberate heat

exposure can improve our mood and

well-being? Well, it turns out that it

improves mood and well-being, but it

also improves our capacity to feel good

in response to things that would

ordinarily make us feel somewhat good.

Now, this is not a situation where

you're going to be walking around

grinning ear to ear in response to

nothing at all simply because you went

in a sauna. What I'm talking about is

the upregulation of pathways, meaning

chemical pathways in your brain and body

that allow you to experience pleasure in

all its fullness. Many of you have

probably heard of endorphins. Endorphins

are a category of molecules that are

made naturally in your brain and body

and that are released in response to

different forms of stressors. That's

right, in response to stressors. of ever

you've gone out on a long run and at

some point in that run you feel like

you're aching and your joints hurt or

maybe you have shin splints and you push

through that

part of the reason that you experience a

lack of pain at some point usually or

you experience a euphoria during or

after that exercise is the exercise

induced effects on endorphin release or

rather to be more specific I should say

the exercise induced consequences on the

stress system which in turn trigger the

release of endorphin. In other words,

when we experience short-term or acute

stress, the endorphine system is

activated. Now, the endorphine system is

not just about feeling good, believe it

or not. It's also about feeling bad. And

there two general categories of

endorphins. The first are the ones that

you normally hear about, endorphins,

things that bind, for instance, to

receptors like the mu opioid receptor.

We make endorphins that naturally act as

pain relievers and that make us feel

mildly euphoric. We also make endorphins

such as dinorphine. That's d y n o r p h

i n. Dorphine

that actually make us feel worse in

response to stressors.

When we get into a hot sauna or a hot

environment of any kind, dinorphins are

liberated in the brain and body. And I

should mention that dinorphins are made

by many neurons in many different areas

of the brain. So you might think, well,

why would I want that? Why would I want

to release dinorphine into my brain and

body? Well, first of all, when you get

into an uncomfortably hot situation,

uncomfortably hot scenario, oh gosh,

this is sounding terrible. A

deliberately hot environment that you

are using to try and trigger some sort

of biological or psychological benefit.

I should say the discomfort that you

feel the desire to get out of the that

environment is in part the consequence

of the release of dinorphine.

It's also the consequence of the

activation of that sympathetic nervous

system. Remember the preoptic area can

communicate with the amydala and trigger

that kind of fight orflight mode. I want

to get out of the sauna. This is really

really hot. But dinorphine is also

liberated from a certain number of

neurons. Dinorphine binds to what's

called the kappa receptor. The kappa

receptor binds dinorphine and triggers

pathways in the brain and body that lead

to agitation to stress and believe it or

not to a general sense of pain. This is

why you want to get out of the hot

sauna. And remember, if it's unsafe

levels of hot, then you should get out

of that sauna or other hot environment.

But if you're working in a range or

you're exposing yourself to a range of

heat that's uncomfortable but safe to be

in, dinorphine will be liberated from

these neurons bind to the kappa

receptor. And as a downstream

consequence of that, there will be an

increase in the receptors that bind the

other endorphins, the endorphins that

make you feel soothed, that make you

feel happy, and that make you feel mild

euphoria. It's fair to say that every

time we get into a hot environment

that's uncomfortable or a cold

environment that's uncomfortable,

dinorphine is likely released and

binding to the kappa receptor.

But over time, that binding of

dinorphine to the cappa receptor leads

to downstream changes in the way that

the feel-good endorphins, things like

endorphin binding to the muopioid

receptor, and there are still other

feel-good endorphins, so to speak. That

system becomes much much more efficient

such that people feel an elevation in

their baseline level of mood. And when a

good or happy event comes along, they

feel a heightened level of happiness or

joy or awe or improved mood in response

to that. So what does it mean? It means

that a little bit of discomfort as a

consequence of deliberate heat exposure

while in the short term doesn't feel

good by definition. It is activating

pathways that are allowing the feel-good

molecules and neural circuitries that

exist in your brain and body to increase

their efficiency, placing you in a

better position to be joyful in response

to the events of life. We're starting to

see a general picture that using the

sorts of sauna protocols that I've

described throughout this episode,

right? five to 20 minutes or so done one

to seven times per week is associated

with a general improvement in

cardiovascular health, a general

improvement in mental health. And it

really points to the fact that yes,

sauna done acutely for three or four

times a day, 30 minutes each session,

separated by a cooling, maybe getting

into cold bath, sure that can potently

increase growth hormone, but done on a

more regular basis can reduce cortisol,

improve heart health, improve mental

health, and for that reason and the fact

that for most people it is conceivable

to come up with a way that you could get

into deliberate heat exposure for a

minimum of cost, right? if it's a hot

bath or if you had to resort to, you

know, bundling up and going for a jog,

this sort of thing. Or if you have

access to it, a sauna of some sort that

we're really talking about a stimulus to

initiate a large number of different

biological cascades that wick out to

improve multiple aspects of brain and

body health. Each protocol that I've

talked about today, whether or not it's

five minutes or 20 minutes or four times

in a day or three times per week or

seven times per week, is tickling or

pushing or stomping, if you will, on a

given pathway and really activating it

to a milder to severe degree. What I've

tried to do today is to illustrate the

general mechanisms by which heat in

particular can activate certain

biological pathways so that you can

devise protocols that are going to be

optimal for you and your needs. So, just

to briefly recap,

if you want to get the greatest growth

hormone increases, do sauna or other

deliberate heat exposure fairly seldom,

probably no more than once per week,

maybe even less, and do it a lot that

day. Just make sure that you break it up

into multiple sessions. In the study I

described earlier, they did four

sessions, 30 minutes each, but that was

just once a week. If you're interested

in the cardiovascular benefits and the

potential longevity benefits of sauna,

well then it's clear that doing it three

to four, maybe even seven times per week

is going to be more beneficial than

doing it just one or three times per

week. And again, that range of 80 to

100° C is going to be your guide. And in

terms of the mental health benefits, it

seems that getting a little bit

uncomfortable in that heat environment,

sauna or otherwise, provided it's safe,

is going to be the best way to access

those mental health effects by way of

increasing dinorphine, which as you

recall, will then increase the ability

of endorphin to have its positive

effects on mood after you get out of the

sauna or other deliberate heat exposure.

And in terms of timing, after a workout

of any kind, morning or afternoon or if

you're not doing it after a workout,

certainly in the later part of the day

is going to be most beneficial as it

relates to sleep. But of course, there's

a caveat there, which I will mention

again, which is that for those of you

that have no trouble sleeping because

you're exhausted or you're just one of

these phenomenal sleepers, well, then do

it any time of day or night. But for

most people, doing it later in the day

is going to be more beneficial because

of the post sauna cooling effect and the

relationship between cooling by a degree

or more as a way to enter sleep. Thank

you for joining me today for my

discussion about the science of heat and

heating for health. And last, but

certainly not least, thank you for your

interest in science.