The Science & Health Benefits of Deliberate Heat Exposure | Huberman Lab Podcast #69

- 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 talking about the science of heat,

and more specifically the science of heating, the verb,

meaning how our body heats up

from both the outside and the inside.

Heat is a remarkable stimulus,

meaning when we are in a hot environment,

it has a profound effect on our biology.

And heating up from the outside,

or as you'll soon learn, from the inside,

has a profound effect on many different aspects

of our health, including our metabolism,

both in the immediate and long term;

our cognition, meaning our ability to think

more or less clearly.

And if you're immediately thinking that heating up

makes you less capable of thinking, you're wrong.

Heat applied properly as a stimulus

can engage certain neurochemical systems

in your brain and body

that can allow your brain to function far better.

We will talk about those data today.

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're also going to talk about the very exciting new science

around local heating.

That is the use of heat applied

to specific areas of the body in order to heal

or improve tissues at that location that you are heating

as well as your biology and health overall.

In fact, we are going to talk about one

very recently published paper

that came out in the journal Cell.

Cell is one of the three apex journals,

meaning three of the most competitive,

most rigorous scientific journals.

Those are Nature, Science, and Cell.

This particular paper was published in Cell,

and I will go into it in more detail later,

but basically what this paper shows

is that by locally heating up skin and fat,

you can change the identity of certain fat cells

at that location and elsewhere.

We have three kinds of fat,

white fat, beige fat, and brown fat.

And as you will learn more about soon,

white fat is not very metabolically active.

It's more of a fuel reserve.

It's what we typically think of as blubbery fat.

Beige fat and brown fat are rich in mitochondria,

and those mitochondria provide a sort of furnace

or heating mechanism for your entire body

and increase your metabolism

and the burning of white fat.

So in other words,

having more beige fat and brown fat is a good thing.

And it turns out that the proper application

of heat to specific areas of your body

can increase the conversion of white fat to beige fat.

In other words, turn an innocuous fuel source

into a metabolically active tissue

that can help you burn off more white fat.

I think many people are going to be interested in this paper

and the tools that emerge from this paper.

It's a fascinating set of findings

that actually emerged from an understanding

of the biology of burn and people who receive intense burns.

And that is not what I'm going to recommend to you

as a tool, of course,

but understanding a little bit about how burns

impact our biology and health

has allowed these pioneering researchers

to develop new tools to combat

obesity and metabolic disorders,

and that you can apply for basic things like fat loss.

I'm pleased to announce that the Huberman Lab Podcast

is now partnered with Momentous Supplements.

Our motivation for partnering with Momentous

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I'm pleased to announce

that I am hosting two live events in May 2022.

The first live event will take place

in Seattle, Washington on May 17th.

The second live event will take place

in Portland, Oregon on May 18th.

Both are part of a lecture series entitled

The Brain Body Contract,

during which I will talk about science

and science-based tools,

many of which overlap with the topics

covered on the Huberman Lab Podcast,

but most of which will not

and will be completely new topics and tools

never discussed publicly before.

Both live events will also include

a question and answer period,

during which you, the audience,

can ask me questions directly

about any aspect of science or science-based tools,

and I will attempt to answer them.

Tickets for the two events, again,

Seattle on May 17th and Portland on May 18th,

are both available at hubermanlab.com/tour.

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.

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Okay, let's talk about heat,

more specifically, let's talk about

the biology of heat and heating

and the health benefits and tools

related to heat and heating.

The first question that we have to answer

is how do we heat up?

And the answer to that question is 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.

Our body has the capacity to generate more heat

or to cool down, meaning to turn off the heating process,

and it can do that in ways

that match the external environment.

The simplest way to think about this

is that we actually have two body temperatures.

People will say, "Oh, what's body temperature?

"98.6."

That's actually not true.

Body temperature varies between individuals.

It varies across time of day within individuals.

And 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.

And as you can imagine,

the temperature of your core

is always higher than the temperature at your surface.

So the important thing to know

is that you have a temperature at your shell

and a temperature at your core.

Now you don't need to know exactly

what those temperatures are in most cases,

but 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,

which makes total sense.

This is a lot like a thermostat in a room,

which is essentially paying attention

to how cold or hot it is,

and then sending signals to the heating or cooling system

to either heat up the environment

or cool down the environment,

depending on the temperature in that environment.

Your brain has neurons that send signals

to other cells in your body

and deploy the release of chemicals in your brain and body

to heat you up when you are too cold

and to cool you down when you are too hot.

So, if you can understand

that you have two body temperatures,

one at your shell, the surface,

and one at your core, inside,

and that your body and brain are always trying

to balance those two temperatures in the appropriate way,

well then you're halfway there

to understanding the biology

of thermal regulation and heating,

and you'll be a lot further along

in understanding how specific tools can be used

to improve metabolism or improve cognition, for instance.

In fact, later you will learn

that one way that you can heat up

is by cooling down the surface of your body.

That's right.

If I were to throw a cold towel, ice cold towel,

onto your torso right now and ask you,

"Well, how do you feel?"

You'd say, "Oh, that's cold, that's chilly."

However, because your brain is acting like

a bit of a thermostat as the surface,

the shell of your body felt cool,

it would make sense that that thermostat

would activate biological mechanisms

that would heat up your core.

Similarly, if I were to put you into a very hot environment,

you'd say, "Oh, wow, it's really, really warm in here,"

but your brain and your body would go

through a lot of effort to activate mechanisms

to cool you down.

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, et cetera,

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.

And as a final point about this,

if you want to develop the best tools,

leveraging heat for your biology and health and performance,

you want to understand heat as a process,

as a verb, as heating, not just heat,

because there's the temperature that you are at

before you encounter the heat stimulus,

before you get in the sauna, for instance,

during the heat stimulus, so while you're in the sauna,

and then afterward.

Everything in biology is a process.

So as you'll soon learn,

there is a specific sauna protocol that can allow you,

can allow anybody, in fact,

to increase the amount of growth hormone

released into their brain and body 16 fold.

That's right, 16 fold.

However, it involves shifting from a hot environment

to a cool environment, to a hot environment,

to a cool environment, over and over and over again,

over a very short period of time,

because it engages a switch, a process,

that compounds, it builds on itself,

to increase growth hormone further and further.

In fact, if you were to just get into a sauna

for a very long period of time and crank up the temperature

to match the exact temperature that was used in that study,

you would not experience those increases in growth hormone.

It really is the transition

between hot and cool temperatures

that engage the process of heating

and reheating over and over again.

So, today you're going to learn about the use of sauna.

You're going to learn about the use of other heat-related tools

for health and optimization,

not just for growth hormone,

but also metabolic health, for controlling cortisol,

even to impact mental health in positive ways.

And in order to do that,

you need to understand a little bit about the mechanisms

of how you heat up and how you cool down,

where the cells and circuits are in the brain and body,

how those cells and circuits work.

I promise to make the description of that

which follows very clear,

even if you don't have a background in biology.

And once you have that in hand,

along with the understanding you now have

about the fact that you got a shell and a core,

and you need to think about both the shell and the core,

well, then you will be in the best possible position

to use sauna or hot tub or other tools,

even just a hot shower,

as a powerful stimulus to optimize your biology.

Now, the science of heat and heating

and cold and cooling, for that matter,

goes back well over a hundred years.

In fact, it's kind of amusing to me

that nowadays there's a kind of renewed interest

in the use of heat and cold

and the science of heat and cold,

because this was the first topic that I studied

as an undergraduate.

And in fact, I did my graduate thesis on thermal regulation.

And at the time, thermal regulation wasn't really considered

one of the hot topics in neuroscience.

People were more focused on things

like memory and consciousness.

And of course those topics are still of vital interest

to many people in many laboratories,

but thermal regulation was considered

more a thing for the physiologists.

Nowadays, not just on social media,

not just in the landscape of biohackers and athletes,

but in the landscape of mental health, and frankly,

in the general ethos around health optimization,

people are really interested in heat and cold.

And the reason they're so interested in heat and cold

is that a lot of the science has been done

both in animal models in mice and in humans

and translates immediately to protocols that anyone can use.

Now, 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 neuron's in the central nervous system,

the brain and spinal cord,

once they're damaged they don't come back.

So hyperthermia is a serious thing to avoid.

Later I'll talk about ways

to rapidly protect against hyperthermia,

but I do want to give everybody a cautionary note up front.

Obviously, if you're pregnant, nursing,

if you're very sensitive to hot environments,

you want to stay out of saunas and things of that sort.

I'm sure there are exceptions to that.

You definitely have to talk to your doctor

if you're going to violate that rule.

And for everybody, you want to approach

any kind of tool related to heating very cautiously.

You always have the opportunity

to increase the temperature later.

So proceed with caution.

Be smart about it.

I don't just say of that to protect me.

I say that also to protect you.

So now let's talk about

what are the circuits for heating up?

How does that happen?

Many of you have probably experienced a fever.

How does that happen?

What happens when you go into a cold environment

and you're shivering,

but you put on a coat and then you feel warmer.

What's really going on there?

Well, 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.

I'm going to throw a little bit of nomenclature,

a few new words at you.

You don't need to memorize these words, except for one,

actually you need to memorize one acronym,

but it's very easy.

It's called the POA.

If you remember POA,

you'll be home free for the rest of the episode,

but I know that there are some aficionados out there

and people interested in getting

a little bit deeper mechanism.

And I do think it's important to understand the circuit,

because once you stand 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's 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 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 parabrachial area,

but it's a relay station.

The lateral parabrachial 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 that you heat up.

That's right.

If neurons in the preoptic area

receive an electrical signal

through the circuit I just described,

that goes from skin to dorsal horn of the spinal cord,

to lateral parabrachial,

they will start sending signals

out to the organs of your body and the tissues of your body

to get those organs and tissues to do things.

And believe it or not, your POA, your preoptic area,

will actually change the way

that you think and feel immediately.

For instance, if something warm contacts your skin,

or something very hot contacts your skin,

the preoptic area will send signals

out to the endothelial cells,

the blood vessels both of the brain and body

that get them to dilate,

to essentially increase their volume and their surface area

in order to cast off heat.

You will also start sweating.

That sweating response is initiated,

not by the hot day or the hot sun,

but by the preoptic area neurons

that send signals out to what's called

the periphery of your

and other chemicals are released,

things like acetylcholine, that get you to sweat.

And if you happen to be shivering,

neurons in the preoptic area

will make sure that you stop shivering.

You're probably familiar with the feeling

of being somewhat lethargic,

or spreading out your limbs on a hot day.

Well, that is the result of neurons in your preoptic area

impacting your musculature

to get you to increase your surface area

so you can sweat off or release more heat.

So there are 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 vasodilation,

the dilation of your veins in particular

and capillaries in particular.

These sorts of things.

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 the circuit

that I just described.

In fact, I just got back from a visit to a very warm place,

and it was remarkable to me how lethargic I felt

in the afternoons.

I just felt like a total slug.

I just could not move or rally to do anything,

except if I waited until the evening,

even though it was later in the day,

even though I hadn't napped,

as the temperature in my environment cooled off,

as my body temperature cooled off,

I felt like I had more energy.

I was actually waking up,

even though I had been awake for longer.

So the relationship between temperature and lethargy

is a very intimate one.

If we're warm enough, we feel active

and like we want to move around.

If we're too warm,

we feel like we need to stay put

and spread out our limbs and dump heat.

And that brings me to a quick and kind of fun point

about how we dump heat versus how other animals dump heat.

Many of you know, of course, that we dump heat by sweating.

Other mechanisms as well, some of which I described,

but that's our main way of dumping heat.

Other animals like dogs don't have the capacity to sweat,

at least not very much,

so they pant in order to dump heat.

And still other animals, like rodents,

when they get too hot they spit on their paws

and they rub that spit on the surface of their body,

which might sound kind of gross,

and probably will get you to think twice

before petting any of those animals

or holding any of those animals again,

unless that's your thing.

Now, one other key thing to understand

about this circuit related to heat

is that the preoptic area

also can send electrical signals to the amygdala,

a brain area that is often talked about

in the context of fear,

but is really just a brain area

that can activate your sympathetic nervous system.

The sympathetic nervous system

is part of your autonomic nervous system

and is the one associated with fight or flight,

or with the stress response,

or even just the excited response.

The sympathetic nervous system is also what gets activated

when you're really excited about something.

The preoptic area has the opportunity

to trigger the activation of the amygdala.

Now, it doesn't do it every time, but it can.

And it tends to do that when you are suddenly

in an environment that feels too hot,

that you feel is risky levels of hot.

If you ever have gotten into a sauna

that was very, very hot, maybe 210 degrees Fahrenheit,

you sit there for a minute.

You'll notice that your heart rate increases,

and there are reasons for that,

and we'll talk about some of the health benefits of that

in a few minutes, but it's pretty uncomfortable.

You may not feel like your skin is going to burn up,

but you often will feel the impulse to get out,

especially if you stay in there for a little while.

That impulse is the consequence of this preoptic area

communicating with your amygdala saying,

"Hey, this environment is really hot,

and I'm tryin' to cool down,

and it's not really working.

I'm dumping heat, but I'm not able to adjust

the core of my body temperature

in ways that are going to protect my neurons.

And so it's a signal that you probably

shouldn't stay in that environment too long.

Now later we'll talk about the advantage

of pushing yourself a little bit through

some of these very hot environments,

provided you can do it safely,

but the impulse to get yourself

out of a very hot environment

is the consequence of the POA

communicating with your amygdala,

and the amygdala then, in turn,

activating your adrenal glands,

which 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.

And then the preop area can kick off

a bunch of autonomic subconscious responses to heat,

which make us attempt to get cooler,

things like sweating, vasodilation, et cetera,

and it can kick off behavioral responses,

spreading out our limbs in an attempt

to dump even more heat;

feeling lethargic, so a lack of desire to run and move;

and it also has the opportunity to kick off

a mild, or maybe not so mild,

panic response to get us out of that hot environment.

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.

Next, I'd like to talk about the use

of deliberate heat exposure, including sauna,

but other tools as well,

as a way to understand how heat

and heating changes our biology.

So, you're going to learn some mechanism

and you're going to learn some tools.

But first I'd like to just emphasize

that 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,

and yes, I will provide a link to these in the show notes,

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.

And 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.

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,

'cause I do realize that a lot of people

don't have access to sauna.

First off, the temperature ranges that were used

in this and pretty much all the studies

that I'm going to talk about,

unless I say otherwise, are between 80 degrees Celsius,

meaning 176 degrees Fahrenheit,

and 100 degrees Celsius,

meaning 212 degrees Fahrenheit.

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 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 five to 20 minutes per session.

And as you'll soon learn,

very brief periods of just five minutes of heat exposure

can be a powerful stimulus

if the heat exposure is significantly great enough for you.

20 minutes can also be beneficial,

but 80 to 100 degrees Celsius,

meaning 176 degrees Fahrenheit to 212 degrees Fahrenheit

is the general range that this and most studies use.

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.

And what they saw was really remarkable.

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,

again at the temperature levels

and the duration that I talked about earlier.

And as you can imagine, the duration,

the temperature levels were related.

So if people went into very hot environments

that were really uncomfortable for them,

maybe they only went in for five minutes.

Whereas, if they were more comfortable and heat adapted

in a given environment or their tolerance for heat

was just simply higher for whatever reason,

well then they tended to stay in longer.

We can take a sort of average

of this five to 20 minute range,

and today we're mainly going to talk about exposures

between 10 and 20 minutes at temperatures between,

again, 80 degrees and 100 degrees Celsius,

176 degrees Fahrenheit, or 212 degrees Fahrenheit.

So these data point to the fact that going in the sauna

two or three times per week is really beneficial

and can lower mortality to cardiovascular events.

And in fact, the benefits were even greater

for people that we're going into the sauna

four 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.

So these are really impressive, and frankly,

encouraging studies.

Certainly they caught my eye and encouraged me

to start using deliberate heat exposure on a regular basis.

What's particularly nice about this study,

and the related study that, again,

is linked in the show notes,

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,

27% less likely to die of a cardiovascular event

for those that went in the sauna two to three times a week

and 50% less likely to die of a cardiovascular event

for those that went into the sauna four times per week,

as compared to just once a week.

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 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 for saying,

how likely are you or somebody to die

from a cardiovascular event,

but maybe be also from some other event,

some other health-related 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 week,

greatly improves,

meaning statistically significant improvements in longevity

in the sense that people are less likely

to die of cardiovascular events

and other things that kill us.

So I and many other people

who are interested not just in our own health,

but in educating about health-related tools

to the general public, find this really exciting.

But knowing what we know about how heat impacts our biology,

it probably shouldn't surprise us

that this sauna type exposure

or deliberate heat exposure has these incredible effects.

So before we get into the biological mechanisms

of how heat can have all these impressive health effects,

I want to just talk about the use of sauna as a tool

and emphasize that 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 a bit,

not too much, not too little,

but that you heat those up.

And no, you do not need to carry a thermometer around

or place a thermometer into your core.

In laboratory studies and in humans,

if you really want to know someone's core temperature,

basically you try and put the thermal probe

as close to the core as you can.

So typically that's done rectally or a mouth thermometer

or even up the nose.

You don't need to do any of that.

This isn't a laboratory study.

There are ways to create a hot environment

such that you heat up your shell and your core safely

without having to measure your core temperature all along.

If you want to do that, be my guess,

but I'm not going to provide a protocol.

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 saunas,

there are hot tubs,

and there are simply rooms that you crank up the heat.

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 you have

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.

So just to be clear, the temperature range is important.

You want to get between 80 and 100 degrees Celsius.

Now you know the conversion to Fahrenheit.

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 hoodie or a wool hat and a hoodie,

or you could do like the wrestlers do,

and you could actually buy one of these plastic suits.

They're literally called plastics

that 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.

Especially if you do it on a hot day,

but of course be careful, hydrate and don't overheat.

Don't become excessively hyperthermic,

'cause you can get heat stroke and you can potentially die.

But if you're going to use sauna,

often I get the question how hot should the sauna be?

Well now you know.

How long should you be in there?

Five to 20 minutes per session.

Although, I will talk in a minute about ways

to optimize hormone output,

in particular growth hormone output,

by doing four very brief sessions.

So maybe not a continuous session.

We'll get into that in a few minutes.

And, of course, you have to ask yourself

wet sauna, dry sauna.

You know what?

Doesn't matter.

Use what you prefer.

Many people ask me, "Well, what about infrared sauna?"

We have an entire episode all about the use of light

and low level light therapy, including infrared light.

It does have certain benefits for skin

and other organs and tissues of the body, if used properly.

My understanding, or at least my assessment,

of most infrared saunas out there

is that they don't get hot enough.

They don't get up to that 80 to 100 degrees Celsius range.

Some do, most don't.

So what you end up with is a situation

where you've got a red light,

low level light therapy stimulus,

and you've got a sauna that's not quite hot enough.

And there are a lot of ideas and claims

about how they work together

in order to get you improved benefits.

I personally am of the stance,

based on the literature that I've read,

that you want to get into those ranges

of 80 to 100 degrees Celsius

before you start considering whether or not

you're also going to include red light therapies, et cetera.

So there's nothing special about red light sauna.

It's really the temperature of the sauna

that you happen to get into.

So which tool?

Which sauna?

Which stimulus?

Do you run wearing plastics and a hoodie and a wool hat

or do you get into a sauna?

That's going to depend a lot on your circumstances,

your budget, and what you have access to on a regular basis.

This is a lot like our discussion about the use of cold.

Most of the studies have looked at immersion in cold water

up to the neck,

because that's a very controlled situation

that you can do in a laboratory.

They have not explored cold showers as much,

So there's just less data,

or walking around in a cold environment.

But we'll talk a little bit about those data,

because as you'll soon learn, when you talk about cold,

you're actually talking about heating as well.

So what kind of mechanisms are activated

in your brain and body

that allow for the various health benefits

of sauna or other forms of deliberate heating?

Well, we talked about reduced risk

of cardiovascular event related mortality

and all-cause mortality.

As you'll soon learn,

there are also tremendous benefits

in terms of increases in growth hormone,

reductions in cortisol, et cetera.

I will detail those.

So what happens when you do get into a hot environment?

What are the mechanisms

that allow for the various health effects of that?

Well, your shell, your skin, senses that.

And through the circuit that I described earlier,

activates neurons in the POA, the preoptic area,

which in turn activates mechanisms

in your autonomic nervous system, like vasodilation.

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, et cetera, et cetera.

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 or 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, this 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 five to 20 minutes,

12 minutes.

The temperature of those saunas

was 90 to 91 degrees Celsius.

So I'll just quickly do the calculation,

admittedly, not in my head.

That's 194 degrees 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 degrees, which is,

10 degrees Celsius is 50 degrees Fahrenheit.

And then they measured hormones at various times

throughout this study, before, during, and after.

They looked at testosterone,

they looked at DHEA, which is in the androgen pathway.

They looked at prolactin and they looked at cortisol.

The significant effects of the protocol

that I just described were on cortisol,

a so-called stress hormone.

So-called because when we are very stressed

for long periods of time,

cortisol levels tend to increase dramatically.

But I should point out that a increase in cortisol each day

right about the time of waking,

and specifically right about the time of waking,

is actually beneficial for our alertness and our energy.

So having some increasing cortisol every 24 hours

is a good thing, provided it happens early in the day.

Late day increases in cortisol

are associated with depression.

That's been shown by studies at Stanford and elsewhere.

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 longterm stress,

and are looking for ways to control their stress.

Controlling your cortisol is tricky.

In the episode on stress,

I talked about supplements such ashwagandha

that can be used to limit cortisol,

but you have to be careful not to use ashwagandha

for extended periods of time,

meaning for longer than two weeks,

because you can get into other issues.

I talk about breath work protocols

that can allow you to clamp or reduce

the stress response in real time.

Again, see that episode for those,

but many people are overworked.

They're overstressed.

They're, 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 12 minute exposures

to 90 degree environment,

that's again, 90 degree Celsius,

followed by a six-minute cool down break

in cool water, 50 degrees 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

that's not a completely zero cost tool,

'cause you need to heat the water

and 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 over all.

Now, I mentioned they did look at these other hormones,

and I'll just tell you

that they did not see significant shifts in testosterone,

prolactin, DHEA, et cetera, using this protocol.

As you'll soon see, there are other sauna protocols

that can impact those other hormones.

So if you're seeking to use sauna to reduce stress,

I think this is a very interesting

and potentially useful research-backed protocol.

And again, we will provide a link to the paper

if you'd like to read more about the data.

So that is one set of biological effects on cortisol

and the related protocol.

What about some of the other benefits of sauna?

Well, we'll talk about those,

but I want to talk about those in the context

of the underlying mechanisms,

because if you understand those underlying mechanisms,

you can really tailor your sauna protocols

for your particular needs.

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're 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 it's texture.

Raw meat is different than cooked meat,

to be quite blunt about it.

Heat changes the quality of proteins,

not just in terms of how they taste,

but the way in which they are configured.

It changes it right down at the molecular level.

When your body goes through changes in temperature each day,

and we'll talk about those changes,

but 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, sort of a protective mechanism,

making sure that proteins within the cells

of your brain and body don't fold in the wrong ways.

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's some interesting studies that were carried out

in animal models that really nicely

mechanistically support the role of heat shock proteins

in some of the benefits of deliberate heat exposure.

Some of these studies were done in flies,

meaning Drosophila, fruit flies,

'cause there are great model organism,

because you can delete genes or add genes easily.

Other studies have been done in mice.

And now there are also studies being carried out in humans,

and I will talk about those.

One of the more dramatic examples

that's always touted in this field

of deliberate heat exposure as it relates to longevity

is that if they expose these flies, these fruit flies

to 70 minutes of a heat stimulus that would,

obviously didn't kill them,

but activated heat shock proteins,

it could extend their life by 15%

in a heat shock dependent way.

Meaning if they made flies

that didn't have these heat shock proteins,

well then they didn't see this extension in life.

And this is one of the reasons to use model organisms.

This is not an experiment that you could do in people.

However, 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 overall, and possibly,

and I want to highlight possibly,

possibly extend life.

One such mechanism involves a genetic program

involving a molecule called FOXO3.

FOXO3 is a very interesting molecule,

because it's involved in DNA repair pathways.

DNA repair is part of the process of remaining healthy.

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 in our cells

in a modification of the genes that are being expressed,

puberty being the most dramatic example.

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, it basically is a different human being.

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.

So it's not just the sprouting

of new aspects of our biology.

It's literally the conversion of different brain centers

from one function to another.

That's puberty.

And we'll do a whole episode about puberty.

We actually did an episode on sexual development

that talks a little bit about those mechanisms.

But the point is that throughout our entire lifespan,

genes are being turned on, genes are being turned off.

Genes are being turned on.

Gene are being turned off.

And DNA, the stuff of genes, gets damaged in that process.

FOXO3 sits upstream in a pathway related to DNA repair,

and again, clearing of the senescent 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 FOXO3.

FOXO3 in turn upregulates pathways related to DNA repair

and clearing out of these senescent 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 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 FOXO3,

there are individuals out there

that have either additional copies of FOXO3

or who have versions of FOXO3 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 FOXO3,

more clearance of senescent cells,

more DNA repair, et cetera.

For the rest of us, at least to my knowledge,

I don't have one of these health-promoting FOXO3 mutations.

Remember, mutations can be beneficial

or they can be detrimental.

This, if your goal is to live longer,

is a beneficial mutation.

If you don't have these FOXO3 mutations

that allow you to be a centenarian

at 2.7 times high or likelihood than other people,

deliberate heat exposure is one way

that you can increase FOXO3 activity.

At this point in time,

meaning when looking at the research out there,

it isn't clear what the optimal sauna protocol

is going to be, specifically to increase FOXO3,

and that's probably because there isn't one.

There is no sauna protocol

designed specifically to reduce cortisol

or specifically to increase FOXO3

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 degrees Celsius

as your kind of 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 five to 20 minutes per session for the sauna

as your rough guide of how long to remain in this sauna.

Now, there was a study published just this last year

that was mainly focused on deliberate cold exposure.

I detailed this quite extensively in the episode on cold.

This is the beautiful work of Susanna Søberg.

And that study looked at deliberate cold exposure,

but also sauna exposure.

And that study found that 57,

yes, 57 minutes per week of sauna exposure

in conjunction with 11 minutes per week total

of deliberate cold exposure

was the threshold for getting improvements

in metabolism and increases in brown fat,

this very active fat tissue

that improves mitochondrial function and thermogenesis,

meaning heating of the body.

We'll talk more about brown fat later.

Why do I mention this?

Well, for those of you that are interested

in increasing metabolism,

it does seem to be most beneficial

to do that 11 minutes per week of cold exposure, again,

divided up across two or more sessions.

So it's not 11 minutes all at once,

but shorter sessions,

and to get 57 minutes minimum per week

of sauna exposure, again,

in the temperature ranges that I've talked about here.

And again, it's not 57 minutes in the sauna all at once.

That's 57 minutes total per week as the minimum threshold.

So you might divide that into three sessions of 20 minutes.

And again, I don't think 57 is the magic number.

It could be 60, it could be 64.

It probably could be 55.

Remember your biological systems

are not counting things off minute by minute,

second by second, least not in most cases.

So for those of you that are interested

in improving metabolism, check out the episode on cold,

or just take the Søberg Protocol, as I call it,

which is 11 minutes total per week of uncomfortably cold,

but safe, cold exposure.

So uncomfortably cold means

you really, really want to get out of the shower

or the ice bath or whatever environment,

but you can stay in,

11 minutes total per week divided across a couple sessions

and then 57 minutes per week, or so,

of deliberate heat exposure,

again, uncomfortably,

but uncomfortably hot, excuse me,

but safe to stay in,

probably divided up across three or more sessions.

Okay, so we've talked about the use of sauna

to decrease cortisol.

We've talked about the use of sauna

to increase heat shock proteins.

We've talked about the use of sauna

to increase FOXO3.

Now I'd like to talk about the use of sauna

to increase growth hormone.

Growth hormone is a hormone

that we all naturally secrete from our pituitary,

which also resides near the roof of our mouth.

The signal for the pituitary to release growth hormone

arrives from neurons that exist in the hypothalamus.

So growth hormone releasing hormones,

believe it or not, that's what they're called,

stimulate the release of growth hormone

from the anterior pituitary gland

into the general circulation,

and then 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 adolescents or adolescents 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 a 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 slow-wave sleep.

As we age, less growth hormone is released

during that slow wave sleep.

There are various things

that can promote the release of growth hormone,

and we will talk about some of those other things

in a moment, things like low blood sugar,

turns out, is a stimulus for growth hormone release.

And I don't mean hypoglycemia of the sort

that makes you dizzy and want to pass out.

That's bad.

I mean, not having high levels of glucose and insulin

in your bloodstream.

This is one of the reasons why many people

are drawn to intermittent fasting or even prolonged fasting,

it's because of the reported increases in growth hormone.

I'll touch on those briefly,

but if you want to learn more about those

and what their real impact is

and the extent of growth hormone,

check out the episode I did on fasting.

You can find that at hubermanlab.com.

Certain forms of exercise have also been shown

to stimulate growth hormone release.

And in a few moments,

I'll talk about how exercise and fasting can be combined

or how heat can be combined with exercise

or certain patterns of food intake

to further increase growth hormone.

But before I do that,

I want to review some of the data,

and one study in particular,

that discovered 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.

So let me describe what they did in this study.

They used an 80 degree Celsius environment,

so that's 176 degrees Fahrenheit,

and they had subjects do the sauna for 30 minutes,

four times per day.

So that's two 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.

So, two hours total in this 80 degree Celsius environment.

So that's a lot,

but what they observed was really quite significant.

So they had subjects do this protocol,

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,

cortisol, thyroid stimulating hormone,

thyroid hormone itself,

luteinizing hormone, and follicle stimulating hormone,

which are hormones that essentially drive

the production of other hormones.

We won't get into that too deeply,

but if you'd like to learn about FSH,

follicle stimulating hormone, and luteinizing hormone,

please see the episode on optimizing

testosterone and estrogen at hubermanlab.com.

They looked at prolactin and they looked at growth hormone.

I'll just cut to the chase

and tell you the effects on growth hormone.

In subjects that did this two hour a day,

80 degree Celsius protocol

experienced 16-fold increases in growth hormone.

So they measured growth hormone

before the sauna and after the sauna

and growth hormone levels went up 16 fold,

which is obviously an enormous,

and it turns out statistically significant, effect.

Now, 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 two hour a day

divided 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 two thirds.

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 threefold increase,

but not as great as the one observed on day one.

What does this mean?

And why does this happen?

Well, the reason this happens is because heat,

just like cold, is a shock or a stressor to the system.

In the context of cold,

if you get into a very cold ice bath,

for instance, a five-degree ice bath, even for 20 seconds,

it's known to increase norepinephrine 200%.

It can double the amount of norepinephrine

that you suddenly release into your brain and body,

which actually can have some positive effects.

I'll talk about those in a little bit,

but if you were to do that every day,

you would become cold adapted.

This circuit that compares the shelling core of your body

would adjust in ways that it could either predict

that cold stimulus,

or more likely to create some thermogenetic mechanisms

in preparation for that cold exposure.

This is why, for instance,

people that use deliberate cold exposure

to try and increase lipolysis, the burning of fat,

oftentimes will get results for a while,

but then if they're doing it a lot, a lot,

they stop getting those effects.

I talk a lot about avoiding cold adaptation,

if that's your goal, in the episode on cold,

but similar mechanisms are at play here.

So we have to imagine that

when the subjects got into the sauna on day one,

whatever pathways went

from measurement of temperature at the shell

to changes in temperature at the core

led to these big increases in growth hormone,

which is basically a way of just describing the result

I already told you before.

But 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 effectors

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,

provided you allow yourself to recover,

pretty soon you're running up that hill

and you're not breathing as hard.

There isn't as much burning in your muscles,

et cetera, et cetera.

Your body adapts.

So, one of the key things to understand

about the use of deliberate heat exposure

is if you're going to use it

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 are 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 deliberate heat exposure every once in a while.

An important way to frame this

is actually in the context of cold.

And while you might say, wait,

this is an episode on heat and heating, not cold,

you really can't have a conversation about heat and heating

without talking about cold.

Because, as I mentioned earlier,

if you cool the outside of your body, the shell,

you're actually heating up your body.

In fact, the circuits that control heating of the body

and that control cooling of the body,

for instance, the activation of things like shiver

or fat loss in response to cold and shiver,

those are also controlled by the preoptic area

of the hypothalamus.

So we can take a step back and start to think about

what it would take to design

the optimal protocol for deliberate heat exposure

by looking at cold,

and here's what I mean.

There have been beautiful studies

showing that if people get into a very cold body of water,

four degrees Celsius for 20 seconds.

As I mentioned earlier,

that will cause the a 200 to 300% increase

in norepinephrine.

Norepinephrine is also called noradrenaline.

And norepinephrine and other so-called catacholamines

like dopamine increased dramatically

in this very brief cold water exposure.

And those increases in norepinephrine and dopamine

are known to have long-lasting effects

that generally lead to improvements

in mood, focus, and alertness.

So they're pretty significant.

However, they aren't significant enough

to increase metabolism to a very high degree.

Whereas, other studies have shown

that if people go outside in 16 degree Celsius weather

with a proper amount,

but a fairly minimum amount of clothing,

you can experience even greater increases in norepinephrine.

But the time that's required in order

to experience those increases is six hours at,

for instance, 16 degrees Celsius.

So if you have six hours a day to be out there in the cold,

or if you can turn the air conditioning on

in an environment and make it very, very cold, fine.

But basically what I'm describing is that

you can sort of bookend the parameters that you can use.

You can use a very brief exposure to cold or to heat

in order to stimulate heat shock proteins,

growth hormone, et cetera,

or you can use longer exposure

in less intense versions of heat and cold.

You really have to find what's going to work for you

and what you can do safely.

And if you're confused about where to start,

please use the parameters that I described earlier.

First of all, check with your doctor.

As always, make sure that you're somebody

who can do deliberate cold or heat exposure safely,

but that 80 to 100 degrees Celsius,

meaning 176 degrees Fahrenheit to 212 degrees Fahrenheit,

that I keep repeating over and over,

'cause I know somebody's going to ask,

even though I repeat it over and over, which is fine,

I'm delighted to keep saying it,

and to respond if someone asks again.

Well, those parameters are going to kind of

bookend what you should do

in terms of the intensity of the heat stimulus.

How long?

Well, we heard earlier, five to 20 minutes.

Why not start with five and then ramp it up to 10 or 15?

And then if you're feeling really bold

and you really want to crank out growth hormone,

well, then you could do

that 30 minute four times in one day stimulus

every once in a while.

So you have to really figure out

what you're using heat exposure for.

This is one of the reasons why when people say,

is it better to get in a wet sauna or dry sauna?

What's the optimal temperature?

Is it better to take a hot shower

or a hot bath or a hot tub?

To be completely honest,

it depends on what you're going to be able to do regularly,

whether or not you want to do it regularly,

and what your specific goals are.

So the purpose of this episode

is really to arm you with the underlying mechanisms

and to arm you with the general parameters

that are going to allow you

to access the results that you're seeking.

For what it's worth, I personally use a protocol,

and I've been using a protocol for a long time,

that involves trying,

meaning I accomplish this most weeks, not all,

trying to get into a sauna

for three 20-minute sessions every week.

I use a dry sauna, so it's not a steam room.

If I don't have access to it,

I might take a hot bath or something of that sort.

But in general,

I just stick to doing the sauna three times a week.

And I generally will do that either after a workout,

either a cardiovascular workout or a weight workout,

or I will do it later in the evening.

Why later in the evening?

Well, it has to do with the circadian shifts in temperature

that we all experience.

Talked a lot about this in the circadian episodes

and the episodes related to sleep.

But in a nutshell, here's how it works.

Every early morning,

about two hours before your typical wake up time,

your body temperature is at its all-time lowest.

We call that your temperature minimum.

Right about waking your body temperature increases.

In fact, an increase in body temperature

is part of the reason you wake up at all,

unless, of course, you're setting an alarm.

Increases in body temperature

are going to be one of the major things

that wakes up your brain and body.

Body temperature will tend to continue

to increase through the morning.

You'll get that increase in cortisol.

That's a healthy increase in cortisol.

Body tempera will increase into the afternoon,

and then we'll start to drop in the later afternoon.

This general contour can be shifted

by whether or not you exercise, how often you eat,

because of the so-called thermogenetic effects of food.

That is, every time you eat there's a slight increase

in body temperature and metabolism,

but it's not really that significant

to throw off this general contour and rhythm,

but toward the afternoon around four or five o'clock,

most days, depending on time of year,

your body temperature will peak,

and then it will start to drop.

And as your body temperature drops by one to three degrees,

and here I'm referring to your core body temperature,

not your shell body temperature,

you will start to get sleepy

and to transition into sleep

and to maintain sleep throughout the night.

Your body temperature will remain low

until you hit that temperature minimum,

and then it'll start to come up again.

What that means is that when you decide

to do sauna, or cold exposure for that matter,

it's going to be important.

Why?

Well, as I mentioned earlier,

if you were to make the surface of your body cold,

at least in the immediate period after that,

your body temperature will increase.

So for those of you that are challenged in getting to sleep

and are still working on your sleep,

remember sleep is the foundation

of all mental and physical health and optimal performance,

you should try to get really quality sleep

of sufficient duration, at least 80% of nights.

That should be an ongoing goal throughout your lifespan

for a huge number of reasons.

Watch the master sleep episode

if you'd like to hear are more of those reasons

and the mechanisms to make sure that you do that.

But in any event,

cold exposure late in the evening

will start to increase your body temperature again.

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,

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.

However, if you have trouble sleeping,

I would recommend doing the cold exposure early in the day

to match that natural heating,

that natural increase in body temperature

that occurs across the 24-hour so-called circadian rhythm.

Similarly, if you're going to use deliberate heat exposure,

you'd be wise to do that later in the day.

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 or 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 warmish 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.

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 nights sleep,

well, then you would be wise to do your sauna

maybe once or maybe twice a week

in the evening or at nighttime,

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.

So there's a really nice study on this

that I can point you to,

is this study that was published in the journal Stress.

Literally, that's the name of the journal.

I love it when journals have these names

like Pain or Stress.

I find that somewhat amusing for reasons that escape me,

but nonetheless, amuse me.

The title of this study is "Growth Hormone Response

"to Different Consecutive Stress Stimuli in Healthy Men.

"Is There Any Difference?"

And I don't want to go into all the details of the study,

because it's pretty extensive and complicated,

but basically what they did is they had people

do sauna and then gave them a drug

or a condition of having low,

not dangerously low, but low blood sugar.

Or they had them in a condition

where they had low blood sugar and then did sauna.

Or they had them do an exercise protocol

that led them to increased growth hormone

and then had them do low blood sugar.

Basically mixing and matching the various stimuli

that could increase growth hormone.

And what they found was very straightforward.

What they found was that doing sauna once

and then waiting some period of time

and then later that day doing sauna again,

they didn't see the same increase

in growth hormone both times.

First they got a big increase in growth hormone

and then less if they did sauna again.

If they had people do exercise and then sauna,

what they found was exercise could stimulate growth hormone,

but then following it with sauna

did not allow you to get twice as much growth hormone.

In general, anytime you release growth hormone,

you reduce the likelihood

that you're going to release growth hormone again

later that day.

And this partially explains that earlier study,

where if people did this growth hormone promoting protocol

on day one, but then on day three

they didn't see quite as big an effect,

and on day seven they didn't see quite as big effect.

All it basically boils down to is that

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,

and the whole notion of what breaks a fast

is kind of an interesting conversation,

because it's contextual.

Will a sip of coffee break your fast?

Well, maybe probably not.

Will one grain of sugar break your fast?

No.

Will an entire candy bar break your fast?

Yes, it has to do with where your blood glucose is

when you ingest that particular food item.

Not so much what that food item, is per say.

But the bottom line here is if you want to crank out

the most amount of growth hormone,

wait a couple of hours after eating

before getting into the sauna,

or maybe do it before dinner and then prepare dinner...

Do the sauna before dinner, that is,

then prepare dinner, then eat dinner,

and then make sure that you wait a few hours

before going to sleep.

You're going to have to arrange your schedule accordingly.

I know most people can't arrange their schedule perfectly

just to get growth hormone increases,

nor do I think people should approach

health protocols that way.

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 out the exact conditions you need

in order to get the greatest effect

out of that sauna treatment.

These are just some additional tweaks

related to food intake

and low level hypoglycemia and exercise,

that if you wanted to leverage, you could.

So if decreases in body temperature

tend to aid the transition of sleep

and getting out of a hot sauna

tends to promote decreases in body,

it makes sense why you would want to put

your sauna exposure or other deliberate heat exposure

in the second half of your day,

and maybe even right before sleep.

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 nothing to do with cardiovascular effects,

nothing to do with growth hormone or anything of that sort,

but rather have to do with 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 longterm consequences

that people experience.

First of all, we need to ask,

how is it that deliberate heat exposure

can improve our mood and wellbeing?

Well, it turns out that it improves mood and wellbeing,

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 up regulation of pathways,

meaning chemical pathways in your brain and body

that allow you to experience pleasure in all its fullness.

So here's how this whole deliberate heat exposure,

sauna, mood thing works.

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.

So, if 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 endorphin system is activated.

Now the endorphin system is not just about feeling good,

believe it or not.

It also about feeling bad.

And there are 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.

Opioids are not just prescribed compounds

or unfortunately drugs of abuse,

which they are.

We have this opioid crisis

in the United States and elsewhere,

which is a very serious and tragic thing,

but we make endogenous opioids.

We make endorphins that naturally act as pain relievers

and that make us feel mildly euphoric.

We also make endorphins such as dynorphine,

that's D-Y-N-O-R-P-H-I-N-E, dynorphine,

that actually make us feel worse in response to stressors.

When we get into a hot sauna,

or a hot environment of any kind,

dynorphins are liberated in the brain and body.

And I should mention that dynorphins 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 dynorphine 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.

And 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 that environment,

is in part the consequence of the release of dynorphine.

It's also the consequence

of the activation of that sympathetic nervous system.

Remember, the preoptic area can communicate

with the amygdala and trigger

that kind of fight or flight mode,

I want to get out of the sauna.

This is really, really hot.

But dynorphine is also liberated

from a certain number of neurons.

Dynorphine binds to what's called the CAPA receptor.

The CAPA receptor binds dynorphine

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, dynorphine will be liberated

from these neurons, bind to the CAPA 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.

So there've been a number of studies showing

that initially deliberate heat exposure,

by sauna or otherwise,

causes the release of dynorphine.

In fact, I think it's fair to say

that every time we get

into a hot environment that's uncomfortable

or a cold environment that's uncomfortable,

dynorphine is likely released

and binding to the CAPA receptor.

But over time that binding of dynorphine

into the CAPA receptor leads to downstream changes

in the way that the feel good endorphins,

things like endorphin binding to the mu opioid receptor,

and there are still other feel good endorphins,

so to speak.

That system becomes 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.

This is not unlike the effects of caffeine

on the dopamine receptor that I've described previously.

And for those of you that aren't familiar with it,

many of you drink caffeine and love it.

Part of the reason you love it

is because of the release of certain neurochemicals,

like norepinephrine, et cetera,

the energy that it gives you.

Maybe the taste, I would hope, as well,

but caffeine ingestion also causes increases

in dopamine receptor concentration and efficacy.

In other words, it allows the receptors for dopamine

to work better so that

for a given amount of dopamine release,

you experience more pleasure and motivation.

This is a similar mechanism,

but within the endorphin pathway.

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 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.

I confess I'm very excited about the data

on deliberate heat exposure

and improvements in the chemical systems

that underlie good mood.

And just to underscore this further,

the dynorphine system is not unique to heat-induced stress.

In fact, there are beautiful studies and reviews

out there about the role of dynorphine

in stress and depression,

in stress and alcoholism,

just as a brief aside,

and in the future we will do a whole episode

on alcohol and alcoholism,

but turns out that chronic alcohol use and alcoholism

causes changes in dopamine receptors

that make it very difficult for people

to achieve pleasure through things

other than alcohol, and even alcohol.

That's kind of the really diabolical nature of addiction,

which is the thing that initially brings pleasure,

eventually is just required

to maintain baseline levels of dopamine.

And I've talked before, and Dr. Anna Lembke,

when she was a guest on this podcast,

talked about the pleasure pain balance

that exists within the dopamine system.

It is beautifully described

in her book "Dopamine Nation," by the way.

Excellent book I recommend to all people, addicts or not.

Well, in that context of pleasure and pain

it's very clear what the pleasure molecule is.

It's actually a molecule more related to motivation,

and that's dopamine.

The pain molecule, however, appears to be dynorphine.

And the fact that dynorphine is dysregulated

in stress and depression and alcoholism

and the relationship between dynorphine and dopamine

is something that we should all take very seriously.

And for that reason,

I'm very excited about the fact

that deliberate heat exposure

can leverage the dynorphine system

in a short term and an acute way

that allows mood to improve after the sauna exposure.

So, for those of you that don't like heat exposure,

keep in mind that a lot of the observed positive effects

on our biology relate to metabolism,

cardiovascular function, but also mental health.

And along those lines, there is a wonderful study,

again, published in 2018.

I don't know why.

I guess 2018 was a big year

for deliberate heat exposure studies.

The title of this study is "Sauna Bathing

"and Risk of Psychotic Disorders."

And this was a prospective cohort study.

Again, we'll provide a link to this study.

It's a really interesting study

that explored the relationship between mental health,

so people suffering from various forms of psychoses,

schizophrenia and other forms of psychoses,

and use of sauna.

So essentially what this study did

is they looked at a very large number of subjects,

more than 2,000 subjects,

who had no history of psychotic disorders.

They were classified into three groups

based on their frequency of sauna use,

either once a week, two to three to times per week,

or four to seven times per week.

This should call to mind that earlier study

on all-risk mortality and cardiovascular event risk.

And then they explored the hazard ratio

for psychosis specifically,

meaning how likely it was that people

would develop psychotic symptoms

or full blown psychotic illness,

according to their frequency of sauna session.

So, again, this isn't causal, this is correlative.

And according to the data in this study,

what they concluded is that

there was a strong and inverse independent association

between frequent sauna bathing

and the future risk of psychotic disorders

in this population.

Now, this does not mean that going

into a sauna seven times per week

is going to prevent people

from becoming schizophrenic, necessarily,

or from having a psychotic episode, necessarily.

And of course, frequent sauna use will be

related to other health-promoting activities.

But in this study, as in the previous study,

they went to great lengths in order to try

and limit those so-called confounding variables.

Now, of course, this is just one study,

and again, it's correlative, not causal,

but based on the large number of subjects they included,

plus the rigor of the statistical analysis,

we're starting to see a general picture

that using the sorts of sauna protocols

that I've described throughout this episode,

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 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.

If it's a hot bath, or if you had to resort to

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.

So up until now, I've been talking about whole body heating.

So for instance, putting your whole body into the sauna,

which of course is what most people do,

or getting into a hot tub or hot bath up to your neck,

or in the cases where we were talking

about deliberate cold exposure as a means

to increase core body temperature and metabolism,

getting into an ice bath or cold water of some sort

up to your neck or into a cold shower, et cetera.

Now I'd like to talk about deliberately heating or cooling

specific parts of the body,

meaning certain surface areas of your body

as a means to get effects on those particular areas,

as well as at the whole body level.

Numerous times throughout this episode,

I've talked about the dangers of overheating.

So what should you do if you think you or someone else

is hyperthermic, is too hot?

Well, if you understand just a little bit

about the cooling and heating systems

of your shell and core,

there are some terrific tools that you can use

in order to cool off your core quickly.

And remember the core consists of the nervous system,

the spinal cord, and the viscera,

which are really the organs you're trying to protect.

So, being able to cool off the core of your body quickly

can be very beneficial,

and in some cases, it could even save your life.

There is a way to more quickly heat or cool the body,

and that's through specific elements of your shell,

meaning particular skin surfaces.

I've talked extensively about this in the episode on cold.

It was also covered in the episode

with my guest, Dr. Craig Heller,

from the Biology Department at Stanford.

It relates to the so-called glabrous skin surfaces

on the upper half of our face,

palms of our hands, and the bottoms of our feet.

And for those of you that have heard this before

I encourage you to continue to listen nonetheless,

because today I'm going to talk about

specifically how to heat the body or cool the body

through these glabrous skin surfaces.

Very briefly, the mechanism is as follows.

The palms of our hands, the bottoms of our feet,

and the upper half of our face

overly specific types of vasculature,

meaning specific types of veins and arteries

that don't have capillaries between them,

and as a consequence,

heat and cold can move very quickly

from the palms of the hands, the bottoms of the feet,

and the upper half of our face,

and change our core body temperature.

There's a name for these particular vascular structures.

They're called AVAs or arteriovenous astemoses.

Basically veins and arteries interacting directly

without capillaries in between,

which allows cooling of blood or heating of blood

much more quickly than is possible

by applying colder heat elsewhere on the body,

where capillaries intervene between veins and arteries.

These AVAs, arteriovenous anastomoses,

can be leveraged to cool off

your core body temperature very quickly.

The key thing is to get the palms of your hands,

the bottoms of your feet, and the upper half of your face

in contact with a cold surface or fluid

that is cold enough to cool the blood

and the core of your body,

but not so cold that it constricts the veins

just below the palms of your hands,

the bottoms of your feet, or the upper half of your face.

So, not placing ice packs necessarily,

but maybe placing cool towels on the bottoms of feet,

the palms of the hands, and the upper half of the face,

and as they warm up, replacing those with other cool towels.

The exact temperature will depend

on how hot you happen to be.

I can't know that without

knowing your particular circumstances.

If you'd like to learn more about

how to cool off your core very quickly,

and some of the details and some of the technologies

that are being developed to do that,

please see the episode I did with Craig Heller

or the episode on cold.

If you don't want to go to those episodes,

here is a good procedure that you could use.

You could grab, for instance,

a package of frozen broccoli or frozen blueberries.

If someone is really, really warm,

make sure they take off their shoes and socks,

get their feet on top of those.

Ideally get some into their hands as well.

Get some cool compresses and get them onto people's face.

You could, of course,

also put a cool compress on the back of the neck,

on the top of the head.

That would be an especially good idea

if someone were hyperthermic

because of the way that cooling of the brain occurs

under conditions of hyperthermia.

But the key point here is that

just putting cold compresses or cold materials

onto somebody's torso is not going to be as efficient

as cooling those glabrous skin surfaces,

the bottoms of the feet, the palms of the hands,

and the upper half of their face.

Similarly, or I suppose to be more accurate,

I should say, conversely,

there are times when it is desirable

to heat the core of the body.

And once again,

just simply throwing a hot towel over somebody

is not going to be the most efficient way.

If someone is hypothermic, they're too cold,

it is not a problem to cover them with a blanket.

But ideally what you do is you use some warm object

or warm fluid to warm the bottoms of their feet,

their hands, and the upper half of their face.

Of course not so warm that you burn those skin surfaces.

This has actually been examined in studies

from the Heller Lab.

Turns out that, for instance,

to get people out of anesthesia,

it is beneficial to warm their core body temperature.

And of course there is fever,

which you should know is an adaptive response.

While fever is uncomfortable,

and in fact often involves a mismatch

between our perception of our shell

and a perception of our core temperature.

In other words,

there are times when our body temperature is really high,

we have a fever, and yet we're shivering and we're cold.

And that's because under conditions of fever,

the immune system liberates certain molecules

that impact, and in some ways,

intentionally disrupt the preoptic area, the POA,

and the way it normally functions

so that it can override peripheral signals

and simply try and heat the body

and kill whatever pathogen has infected the body.

So for those of you that think about fever

as always a bad thing, it's not.

Now, of course we don't want our core body temperature

to go so high that tissues of the brain and body are damage.

This is one reason why, if a fever ever goes above 103,

you need to start getting a little bit worried, 104.

There are times when you need to call an ambulance

or go to a hospital,

you really need to employ cooling methods

of the sort that I talked about before

to prevent hyperthermia.

Of course, safe ranges for body temperature

vary between infants and adults.

So you can look those up online,

depending on the person's age, what is a safe range,

what is not.

But keep in mind that if you are taking compounds,

pills to reduce your fever,

you are actually short circuiting

the protective mechanism for burning up the pathogen.

And that's because most pathogens,

bacteria and virus, don't survive well at high temperatures.

In fact, in laboratories,

if we want to preserve a virus for use,

we put it into a freezer.

If we want to kill a virus, we heat inoculate it.

So in many ways, fever is your natural form

of heat inoculation designed to kill pathogens

of various kinds.

Now last, but certainly not least,

I want to refer to the study that I described

at the very beginning of this episode,

involving what's called local hyperthermia

in order to trigger a number of biological processes

in fat tissue in order to convert white fat to beige fat,

which is the metabolically active form of fat.

Many of you, or at least some of you,

should be familiar with the fact

that deliberate cold exposure

can increase brown fat stores,

these mitochondrial dense fat stores that can, in turn,

allow a person to feel more comfortable

in cold temperatures, water, or otherwise,

and increase core metabolism.

I talked about this in the episode on cold,

but very briefly, the general protocol, again,

is to get 11 minutes total per week of uncomfortable,

yet safe deliberate cold exposure,

either through ice bath, cold shower,

cold immersion up to the neck,

or some other form of cold exposure.

That triggers increases in brown fat.

That's been beautifully shown by Dr. Susanna Søberg.

And that increase in brown fat

in turn increases core metabolism

and one's ability to feel comfortable in cool temperatures.

This was a study done in humans,

and there's now ample evidence from animal models

to support that this is a general phenomenon

that I think most people could use and benefit from.

Local hyperthermia is a distinctly different phenomenon.

It involves heating a particular surface of the body

as a way to convert the white fat at that location

to beige fat, which in turn leads to more systemic increases

in thermogenesis and increases in metabolism,

and believe it or not, in fat loss.

Now, the study that I'm referring to

is a very recent study that was published,

again, in this terrific apex journal, Cell,

Cell Press Journal.

And again, one of the three top journals,

Nature, Science, and Cell are the three top journals.

Top because they're the most competitive,

but also generally, not always,

but generally the most stringent

in terms of the review process.

Papers that make it into these three journals

generally are of very, very high quality.

And certainly enough people see them that

if they're not of high quality,

they get shot down pretty quickly in a short amount of time.

Whereas papers in other journals

can sometimes last a long time

before they're ever replicated, et cetera.

The title of this paper

is "Local Hyperthermia Therapy Induces Browning of White Fat

"and Treats Obesity."

This was a study that was performed on mice and humans

in the same study.

What this study involved was heating

of a local patch of skin to 41 degrees Celsius,

which is a 105.8 degrees Fahrenheit,

but not damaging the skin.

So the methods of heating

did not involve placing something

on the skin that would damage it.

In fact, in the study on the mice,

they used this kind of clever molecular chicanery

in order to do it.

And in humans, they used a thermocouple

that would allow them to heat the skin up

just locally in particular locations on the body

that I'll talk about in a moment.

They refer to this process as LHT, or local heat therapy.

The reason they did this is worth considering.

It's long been known from clinical data.

And in fact, from a bit of research data

that people that experience burn on a small,

or unfortunately in some circumstances,

significant portion of their body

experience overall decreases in body fat

and increases in metabolism that can last many years,

Now, of course, is not reasonable nor would one

ever want to induce burn in order to induce fat loss.

But the observed increases in metabolism and fat loss

in response to skin surface burn

couldn't be explained by reductions in activity

related to the burn, for instance.

And in fact, there are molecular pathways

related to something called UCP1,

which is uncoupling protein one.

I talked about this also in the cold episode,

but don't worry if you didn't see that episode,

or if you choose not to.

UCP1 has the ability to increase mitochondrial function

in ways that increase core body temperature overall,

in particular, in beige and brown fat,

which are these fat cells that exist

generally along our spine, and in particular,

in the upper part of our back

and around our neck and clavicles.

And they're responsible for acting as this sort of a candle,

or I should say the fuel or the fat of a candle

that can be burned up to manufacture heat in the body.

So, if you normally think about fat

and you think about blubbery fat,

you're thinking about white fat,

which again is just a storage site.

Beige fat and brown fat exist at just a few locations,

mainly internally, around our spinal cord and our clavicles,

and those fat stores are responsible

for generating heat in our body.

So they're a very metabolically active form of fat.

Small children have a lot of brown fat and beige fat,

in particular because very young children can't shiver.

A number of you probably didn't know that,

but very young children can't shiver,

so they need some way to generate heat

in order to make sure that they stay alive

if they were ever to get cold.

This is also probably the reason why little kids

can run around on a cold day outside without their shirt on

and they don't even seem to notice,

whereas adults are freezing cold.

As we get older, the amount of beige and brown fat

tends to either reduce or shrink or disappear entirely.

It's still debated which happens.

But we know that white fat can be converted

to this more metabolically active form of beige fat

by deliberate cold exposure,

according to the protocol I talked about earlier,

and now it seems, based on this new study,

that local heating of skin tissue can also induce UCP1

and the effects of UCP1 on increasing mitochondria.

And in fact, that local hyperthermia, 41 degrees Celsius,

that is 105.8 degrees Fahrenheit,

can actually induce the conversion

of white fat to beige fat.

Now that's pretty interesting,

and I can already predict the way this is probably going to go

in the kind of wellness and biohacking

and longevity communities.

I'm sure that pretty soon there are going to be

people putting heating pads

on different fat pads of theirs on their body,

trying to reduce,

or at least convert the white fat into beige fat.

And who knows, maybe that'll work.

There have not been many controlled studies of this yet.

This is the first, at least to my knowledge,

of such studies looking at this in non-burn conditions.

Nonetheless, the data are mechanistically

even more interesting than this whole business

about UCP1, and here's why.

Local hyperthermia,

using the protocol that I described before,

resulted in the increase of a promoter,

which is essentially a mechanism

by which certain genes regulate their activity.

This is a DNA binding of something called HSF1.

We don't have to go too deep into the mechanism here

or the nomenclature,

but HSF stands for heat shock factor one.

And HSF1 binding to a particular location

in the genome allowed for a different molecule

with a very long name.

I'll just tell it to you for fun,

but you can just let the numbers and letters stream by.

It's not important.

HNRNPA2B1, shortened to A2B1,

which frankly is not that short to begin with, A2B1,

is still a name that should be meaningless

to most everybody, but here's what's really cool.

A2B1 is directly involved in glucose and lipid metabolism

and regulates the genes that control

glucose and lipid metabolism.

So here we have a situation where local heating of skin

converted a metabolically sluggish or inactive cell type,

the white fat cell, into the metabolically charging,

so to speak, beige fat cell, which in turn

led to systemic, meaning body-wide increases in metabolism,

through two mechanism.

One mechanism is this increase in UCP1,

which for those of you that want to know,

UCP1 causes shifts in the way

that potential energy is pushed from the protons

through the mitochondria,

basically more mitochondrial function,

which means more ATP,

which means cells are more active,

AKA, increased metabolism,

and increases in things like heat shock factor one and A2B1,

which are involved in lipid

and glucose metabolism and regulation.

So I want to be very clear,

this study does not say that spot reduction

is possible with local heating of tissue.

I just can see it now that once this paper

gets out into the press, people are going to say,

oh, heating up a certain patch of skin

is going to burn fat or convert fat

to some other cell type at that location.

Sorry, that's not the way it works.

They did observe increases in beige fat cells

at certain locations in the body.

But those increases in beige fat

occurred where beige fat cells always reside,

around the spine, the upper neck,

the clavicles, and so on.

This is exciting because it provides

yet another potential mechanism