Huberman Lab: Dr. Susanna Søberg: How to Use Cold & Heat Exposure to Improve Your Health

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, my guest is Dr. Susanna Soberg.

Dr. Susanna Soberg completed her doctoral thesis work

at the Center of Inflammation and Metabolism

and the Center for Physical Activity Research

at the University of Copenhagen in Denmark.

Her research has focused on how deliberate cold exposure

and deliberate heat exposure

can be used to enhance human metabolism.

She is the first author of a seminal study

which discovered the minimum thresholds

for deliberate heat and deliberate cold exposure

for increasing brown fat thermogenesis,

which is essentially a mode of increasing heat production

and metabolism in the body,

and for establishing actionable protocols

that can be used outside of the laboratory

to improve metabolism and human health.

Dr. Soberg's research was published in the journal

Cell Reports Metabolism in 2021,

adding to a long and important history of research

focusing on the role of cold and the role of heat

in altering various aspects of the body's physiology,

including hormone health, metabolism,

and changes in neurotransmitters

such as dopamine and epinephrine.

In fact, today's discussion with Dr. Soberg

focuses on the role of deliberate heat

and deliberate cold exposure on metabolism,

but it also includes discussion of the effects of cold

and heat on things like neurotransmitter production,

namely dopamine and epinephrine and norepinephrine,

the so-called catecholamines,

which strongly impact mood and metabolism.

In addition, Dr. Soberg answers many common questions

about deliberate cold and deliberate heat exposure,

including, for instance, the difference between cold showers

versus cold immersion up to the neck

versus total body cold immersion,

including whether or not going back and forth

between heat and cold changes fundamentally

the way that heat and cold impact,

the metabolism, hormones, and neurotransmitter production.

And we talk about almost every single nuance and variation

on deliberate cold and deliberate heat exposure protocols

as it relates to the underlying science,

in particular, how cold receptors

at the level of the skin are impacted

versus cold reception and perception

at the level of the brain,

and how all of that impacts systems of the brain and body

relating to mental health, physical health, and performance.

Based on her scientific research

and academic training,

as well as her understanding and use of deliberate heat

and deliberate cold exposure protocols,

Dr. Soberg is considered one of the world's leading experts

on these topics.

In fact, she is the author of a recent book

entitled Winter Swimming,

which is, I have to say, a terrific book

because it breaks down chapter by chapter

the different aspects of deliberate heat and deliberate cold

into its various constituent parts,

including cold acclimation, the cold shock response,

dangers and safeties of cold water,

the impact of cold and the impact of heat

on various aspects of human health,

as well as specifics relating to sauna

versus ice versus cold swimming, showers, et cetera.

It's a very thorough read

and a very easy and accessible read

that if you are interested in deliberate cold

or deliberate heat exposure or both,

will allow you to embrace those protocols

with the greatest degree of confidence

that you're going to obtain the specific endpoints

that you're interested in and to do so safely.

Before we begin, I'd like to emphasize that this podcast

is separate from my teaching and research roles at Stanford.

It is, however, part of my desire and effort

to bring zero cost to consumer information

about science and science-related tools

to the general public.

In keeping with that theme,

I'd like to thank the sponsors of today's podcast.

Our first sponsor is Plunge.

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I've talked numerous times on this podcast

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and indeed today's episode is focused entirely

on the benefits and the science of deliberate cold exposure.

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As we will discuss during today's episode

with Dr. Susanna Soberg, deliberate cold exposure,

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I'm pleased to announce

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Both live events will include a lecture

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Once again, that's hubermanlab.com slash tour

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I hope to see you there.

And now for my discussion with Dr. Susanna Soberg.

Dr. Susanna Soberg, welcome.

Thank you.

So great to have you here.

I feel like I should give a little bit

of the backstory of how we got connected,

which was that for many years,

I've been interested in cold thermogenesis.

It was the topic of my senior thesis in college.

And I've, of course, followed the popularity of Wim Hof

and we've had Dr. Craig Heller, my colleague

from Biology Department at Stanford,

who works on cold and its impact on physiology

and sports performance.

So for a long time I'd been interested in this area,

but there's been a real lack of new,

let's say high profile quality scientific information

in terms of how, for instance, cold plunges and sauna,

how that impacts human physiology.

I know there's been some information out there,

but it's been sort of scattered.

And then a little over a year ago,

I see this paper in Cell Reports Medicine

and it was immediately struck the,

first of all, the fact that it was in Cell Reports Medicine.

I've been on the Cell Press editorial board

for a long time now.

So press journals are of course phenomenal journals.

And the title and the content of the paper

was directly in line with the sorts of practices

that people are very curious about

and then are starting to emerge things like sauna,

cold plunges, and there was your name first

on the author list.

And I reach out to you through social media

and we've done a little bit of live content there together.

And I've been tracking what you've been doing in the world

in terms of your book and talking about the results

in your manuscript and talking about the science

and impact of deliberate cold exposure and sauna.

And I have to say that it's been a wonderful

and remarkable thing to see.

And you're bringing so much quality information

about this area that for a long time,

I think was kind of niche and is now becoming

more and more mainstream.

So I'm gonna start off with a thank you for being here

and a thank you for the work that you've done.

And I'm looking forward to talking to you about it today.

So my first question to get things started is,

what is happening when we get into

an uncomfortably cold environment?

So for instance, if I'm really hot on a hot day,

jumping into a cold pool feels really good.

But if I'm already kind of at room temperature,

I'm a little bit chilly,

getting into that same temperature of water

doesn't feel so good, right?

There's a shock there.

So if you could just walk us through what happens

when we get into uncomfortably cold water,

whether or not it's by way of shower or cold plunge

at the level of our physiology.

And if you'd like our psychology,

I think that's a good place for us to start

because I think it will orient people

to their own experience if they do that.

And for those that haven't done it,

might start to peel back some of the layers

as to what the underlying mechanisms of cold are.

Yeah, thank you for that question.

It's really good to just address

what actually happens in our physiology when we get cold.

And you can get cold in many ways.

So you can just head out for the one

that gives you the most potent stressor,

which is submerging into cold water.

And, but you could also go in outside in the cold wind.

That's also gonna activate your sympathetic nervous system.

So get all these neurotransmitters going in your body

and so your catecholomines.

Let's just address that we are taking a cold plunge,

for example.

So if you are very hot, for example,

before you go into the cold water,

it's gonna feel less stressful,

but the temperature difference from your skin to the cold

is definitely gonna give you a shock,

but your core temperature is warmer

and that's gonna feel a little bit better.

So that's why when people go into a sauna, for example,

and go out into the cold water,

they can do it easily, easier

than if they were cold beforehand.

Could I just ask you a few questions?

So you mentioned the sympathetic nervous system,

which for people listening who aren't familiar with that,

is that the branch of our nervous system

that's responsible for creating accelerations

and heart rates, feelings of alertness,

it's accompanied with stress and the stress response,

but it's accompanied with waking up in the morning

for that matter.

It's not always about stress.

And then you mentioned the catecholamines,

which are dopamine epinephrine and norepinephrine.

So maybe a little bit later,

we'll talk about those individual neurotransmitters,

but you raise a really important point,

which is something I get asked about a lot

for people that are curious about

using deliberate cold exposure,

which is how cold should the water be?

And I know it's very hard to give

a straight prescription for that,

because I think it boils down to what you just said,

which is it's really the difference

between your current temperature

and really the temperature of the surface of your skin

and the temperature of the water.

So if you're very warm, getting into cold feels good.

If you're already cold,

getting into more cold feels stressful.

Is there any way that we can start to gauge

what is the best way to approach

a deliberate cold exposure protocol?

I mean, should it feel uncomfortable?

And that leads into the question of,

how do we balance the discomfort

with the amount of time that we spend in?

So for instance, if it's just a little bit uncomfortable,

we'll spending more time in the cold,

get us the same benefit as getting into

very uncomfortably cold water

for a very short period of time.

Yeah, it's really good question.

And I definitely think that this could be

future studies on this as well to really unravel

what kind of protocols are the best way

or also for which outcomes, of course.

So if the temperature is very cold

and you feel that, and you also feel very cold,

then you should stay in the water a little bit longer.

So I think it's just, you should get uncomfortable cold.

So as long as you get uncomfortable cold,

it's cold enough and you get this,

what we call the cold shock.

So the cold shock is activation

of your sympathetic nervous system

and these activation of the catecholomines,

which you just mentioned before.

Does the shock mean that I'm having trouble

controlling my breathing?

Is that a good gauge?

Yeah, you can say so because that's kind of like

how we define it.

So you hyperventilate.

So you have a faster breathing rate.

So that increases also because you activate

your gasping reflex if you are new to this.

But if you are adapted, it kind of subsides

with time, with adaptation.

So what you can do is that you can train this cold exposure

and you can kind of like get adapted to it.

So you don't have this hyperventilating response

every time you go out in the cold water.

So this is like building up your resilience,

building up your adaptation is gonna make this shock

like subside of it.

So it's always harder in the beginning,

but you should do hard things, right?

It's not something that we,

you shouldn't think about cold water

and cold water immersion as something that is comfortable.

It should be hard because that's the point of it, right?

If you enjoy it, then yeah,

then I'm thinking something is wrong, it's not right.

You should not enjoy it.

Well, this is an important point that you're making

because I think that many people shy away

from deliberate cold exposure because it's uncomfortable

in a way that at least from my experience

is very different than the discomfort of exercise.

Because with exercise, for instance,

if running fast and breathing hard is uncomfortable,

you can slow down or walk.

If lifting weights is uncomfortable,

you can remove some weight

or reduce the number of repetitions or stop.

With deliberate cold exposure,

I suppose you can be sort of halfway in,

halfway out of the water

or partially underneath the cold shower,

but it's very hard to titrate and adjust the level.

It's kind of all or none.

And I've seen, I should just, I can tell this by anecdote,

I've done some work with military special operations.

I won't say which country this was outside the U.S.

And these are very tough individuals.

They're used to going without sleep

and doing hard, high consequence, high risk kind of work.

And they were asked to do some cold water exposure training

and I was there that day.

And it was remarkable.

About a third of them just went straight in

and just kind of grinded through it.

They looked stoic anyway to me.

There were a few whimpers, no cries.

About a third talked a lot

and got really, you could tell that they were agitated

and anxious, but they made it through.

And then about a third of them

just simply would not get in past their knees or thighs.

We're just, it seemed like they were

just dreading the whole experience.

Some actually didn't actually go in completely,

which was really surprising to me

and that you couldn't tell based on their physical appearance

or anything else about them.

They're all high performers as to who would have this response.

So it seems like people vary tremendously

in terms of their ability to embrace

the discomfort of the cold.

Is that from your studies, is that your experience as well

or are there these weird mutants

who seem to just love going into the cold

for the first time?

So some people just feel better in the cold

and some people are dread the cold even more.

And you can say the more people are pushing the cold away,

they might feel the cold pain even more.

So they would definitely,

people who are maybe the soldiers you just talked about,

some of them might be already adapted to the cold.

So if they are not scared of the cold,

they go out and they embrace the cold in a better way.

It could also be that some people

have a more sensitive nervous system.

And when you are a bit sensitive to the cold,

you will of course try to get away from it, right?

And you will also have the cold pain more,

feel the cold pain more if you avoid it.

So the more you avoid the cold,

the more painful it will feel when you go into it.

So yeah.

You mentioned being outside in a T-shirt

versus cold immersion up to the neck versus shower.

I think this is something a lot of people wonder about.

What are the differences in terms of impact?

Short-term and perhaps even long-term

between cold showers, cold plunge to the neck.

So that could be in ice water or just very cold water.

Immersion with dunking one's head and then coming up

because obviously people have to come up for air

at some point.

And then simply being outside on a cold day

in shorts and a T-shirt or something of that sort.

So there are different outcomes

because they are very different exposures of the cold

to your cold receptors in your skin.

So the more you can say you cover your body in the cold,

which you would do in cold water

because they're of course covered totally

and the molecules are closer to your skin,

you will have a more potent activation

of all your cold receptors in the skin.

So that one will definitely activate

your other nervous system more and rapid

compared to going out in a T-shirt, in the cold wind,

just go for a walk.

But that is also something that's gonna activate

your sympathetic nervous system,

meaning that you will have an increase in norepinephrine

and you will activate something called the brown fat.

So this is a healthy kind of fat tissue

that we have in our body.

And when you activate that,

that's gonna increase your metabolism.

Before we talk about brown fat,

and I'm so glad you brought it up

because it's so much to talk about there.

What about cold shower?

I mean, obviously cold showers somewhere in between

being outside in the air, cold air

versus being immersed up to the neck.

If we had more studies on cold showers,

we would learn more about how does that activate our metabolism,

how does that increase our nervous transmitters

in the brain, which could also have an impact

on our mental balance.

So I think that would be interesting for the future.

But what we do know is from activating brown fat

and both from rodent studies, but also in humans,

is that as soon as we get cold on our skin,

we will activate our brown fat.

So it is kind of like our first responder in the body

to keep our temperature up.

So our muscles is like the second tissue in our body.

We have two tissues which can increase our thermogenesis.

So the brown fat, which is always like temperature

regulating our body, and then we have the muscles,

which will secondarily start to shiver

and that's gonna increase our temperature in the body.

But as soon as you go into a cold shower,

you will activate your brown fat also immediately.

So it could be good also for increasing metabolism

in theory because we haven't really any studies showing

how much does actually activate the brown fat.

So if someone out there wants to do a study on that,

that would be great.

I've thought about why there are fewer studies

of cold showers than cold immersion.

And I think the answer to my mind is that

from a methodological standpoint, it's just harder to do

because if people are getting into cold water up to the neck,

they're getting into cold water up to the neck.

Whereas if people are getting into a cold shower,

some people are larger or smaller,

some people are gonna stand under the shower

with it hitting their head,

some people the back of the neck,

you could direct people to do it,

but it's a little bit more difficult.

Also, I think for you and I are both research scientists,

there's a little bit of a methodological challenge

that might seem silly to people, but it's a real one,

which is if people are in a cold shower,

also the water is going to be,

I'm kind of pushing their clothing against their skin.

There's a certain vulnerability for most people

coming to a laboratory in the first place,

let alone being absorbed while they shower.

Whereas when you get into cold immersion,

you're getting under the water.

And some people might roll their eyes

and say, okay, really, is that the barrier?

But science exists in these real world contexts.

And this will vary by culture and things of that sort,

but we run human subjects in my lab

and I'll tell you just the process of getting people

to the laboratory and having them park and find the lab.

And it's a whole new environment with people in lab coats

and people moving around and where's the restroom?

I mean, there's a certain amount of stress

just associated with taking part in a study

for most human subjects.

So I totally agree, however,

we need more studies of cold showers.

It's just a harder environment to control in my mind.

So it sounds like any form of cold to the skin

that people register as what you call the cold shock

or uncomfortable, like this is kind of jarring,

activates the brown fat.

Do we know what the pathway is from cold receptors

on the skin to the brown fat?

I mean, how does the brown fat know that we're cold?

Yeah, really good question.

And it seems that I think that, of course,

in the future we will know much more about these pathways.

But what we do know is that the cold receptors

will send a signal to our temperature regulating center

in the brain, so hypothalamus.

And that's gonna be taking in this message.

And we have so many cold receptors in the skin.

So it's gonna be very fast as you can say,

if you immerse the body into cold water,

this is gonna be so rapid.

So it will have a rapid increase in neurotransmitters

in the brain from no adrenaline.

Adrenaline and cortisol, which is not that much,

but it's still there.

So you have this increase in no adrenaline,

which will then immediately activate the brown fat.

Because you can say the activator is the most potent one,

cold and no adrenaline,

that's gonna activate the brown fat.

There's also a direct pathway

from the cold receptors in the skin to the brown fat,

which really shows that because of these different pathways,

it shows that it could be that this tissue

to keep us warm was developed in our involvement as humans

to keep us warm and to save us

whenever the temperature on our skin varies

to just a little bit,

to keep us in that right homeostatic balance.

So we don't get hypothermic,

but also so we don't get hyperthermic,

but because it seems that the brown fat is also activated

when we get warmer on our skin.

So it's also maybe a temperature regulator in our body,

but the pathways is different.

I think it's also a third pathway

from directly from the muscles.

So the brown fat is also activated

even though the muscles are starting to shiver.

So there's an extra pathway that way

to keep our temperature up.

So muscles and brown fat are working together

to keep us warm.

So we don't suffer too much in the cold water.

It's super interesting.

And what I hear you pointing to

is the existence of three parallel pathways.

And this notion of parallel pathways

comes up over and over again in biology, as you and I know.

And I mean, I think it's important for people to know about

because as you said so eloquently,

the when something is very important to our survival

and our evolution,

the brain and body install multiple mechanisms for it,

not just one.

And so it sounds like it's cold skin,

cold on the skin triggers a response in the hypothalamus

which then activates brown fat,

cold receptors in the skin directly to the brown fat

and then shivering in the muscle to the brown fat.

I wanna talk about brown fat in depth

and learn from you more about brown fat.

Before that, however, I wanna ask about shiver.

I've heard that shiver causes the release of succinate

which then activates the brown fat.

Is it known whether or not inducing shiver is important

and when should people shiver?

I mean, I've gotten into cold plunges and shivered

while I was in there.

And then I've also had the experience of getting into

a cold plunger, a cold shower, then getting out

and even standing outside on a warm day

after swimming in a pool and then starting to shiver.

So the shiver comes later.

So how important is shiver

and does it matter when shiver happens?

Yeah, well shivering is good

because that increases your metabolism

and that was gonna burn some calories in your body.

You shouldn't be so afraid of shivering, I think,

because the shivering, as long as you don't get

too hypothermia, so if you don't sit in the cold water

for too long and what you just said by shivering

after you get up, that is because of the after drop.

Something called the after drop is when your core temperature

decreases even after you get out of the cold water.

And it always does that in your body

because as soon as you get into the cold water,

all your blood vessels is gonna constrict

because you need to keep your blood in your core

and keep your vital organs warm.

So as soon as you get up,

that those blood vessels will open again

and the warm blood would flow out and get colder

and then flow back again into the core

and that's gonna decrease the temperature

in your core, of course.

So that's the drop.

So that's the drop, yeah.

I'm so glad you explained that.

I've heard years ago, Wim Hof,

I heard him talk about the drop

and I've heard colleagues of mine talk about the drop

but that's the first time I've ever heard it explained clearly.

Let me make sure I understand this.

So I get into cold water, obviously I'm cold.

Vessels constrict to keep blood near the center of my body,

keep me alive.

I get out,

the warming up of my body allows those vessels

and capillaries to dilate again.

The blood goes out to the surface

but the surface is still cold

and so that blood is cooled

and then my core body temperature drops

and that's what you're referring to as the drop

and that's what induces shiver.

Exactly.

And then am I right in thinking

that then the shiver activates brown fat

which then warms me up again.

Yes.

Got it.

That's why you should end on the cold

so we can get back to that.

Yeah, let's talk about it.

Yes, ending on cold is,

you know, it's what I refer to as

and what has now become known as the sober principle

which is a really important principle

about the importance of ending on cold

and not doing what I do which is to get into a hot shower

or back in the sauna but we'll get back to that

in a few minutes.

So that's wonderful that you can explain that so clearly

because I think that shiver is something

that a lot of people do avoid.

People think, oh, I don't want the,

you know, the chattering of the teeth

and it feels like a loss of bodily control

which really it is, it's an autonomic response.

Yeah, but I don't think that people should avoid it that much.

It's just like seeing shivering as a way of your body

in a, like it's training.

It's training for your, for all your cells,

it's training for your muscles,

it's training of your metabolism

and that's gonna increase your,

what's called the insulin sensitivity.

So if you can like in your mind get used to the thought

of shivering is just like when you go exercising

in the training center and get that feeling of like,

oh, this is tough.

Now it hurts a little bit.

Yeah, it's gonna hurt

because that's what shivering also does

but it's just a different way of training your cells

in your body.

It's gonna create what is healthy stress.

It's called homeosis in the cells

and the more you expose your muscle cells

or your brown fat cells to these kind

of like healthy stresses, exercise, cold and heat exposure,

it's gonna make them better at like activating

and also at keeping you healthy.

So as long as the cells get exposed to this,

it's gonna keep them on its toes.

You can say because it becomes more robust

increasing these heat shock proteins

and cold shock proteins in the cells

to make you more robust for the next time.

And that is also what happens

when you go to the training center

and I keep like drawing that parallel

because people today know more about,

we know more about exercise

and what that is gonna do to your muscle cells.

But the same kind of like training is also what you do

when you go out and into the cold water

and submerge into cold water

because that is just your cold training center.

You can say that.

And also your heat training center going into the sauna

because the cells are getting stronger

with hermetic stress.

So it's the same process, just different practices.

I'm so glad that you brought up the fact

that the discomfort or the embarrassment

or both of shiver is still crucial to actually

to reach for and try and experience

the same way that with exercise,

I think a lot of people don't realize this

but when we did our series with Dr. Andy Galpin

it became clear to me

what should have already been clear to me.

And I think that most people don't realize

which is that if we were to measure heart rate,

blood pressure, stress hormones and inflammation

in a human being during exercise,

it would look as if they were ready to die.

Blood pressure would be high,

inflammation is through the roof

but all of that is setting in motion

in an adaptation or set of adaptations

that allow blood pressure to be lower at rest,

that allow inflammation markers to be lower at rest.

All the things that everybody is seeking with exercise

in addition to of course the aesthetic changes

that people are seeking with exercise.

Sounds like the exact same things

are happening with the cold.

So the redundant message here seems to be

that the more discomfort provided it's done safely,

just like with exercise,

the more shivering the more cold shock

provided it's not to the extreme

and stop somebody's heart, right?

We can talk about thresholds for that a little bit later.

It sounds like all of that is going to set in motion

some long-term changes that will make people feel better

and will improve health.

Could you just touch on a few of the longer-term changes

that are known to occur?

I mean, I'm well aware of the study

showing that I think it was European Journal of Physiology.

It was the European Journal of Physiology

showing long-lasting increases in catecholamines,

dopamine, norepinephrine and epinephrine

for many hours after deliberate cold exposure.

What are some of the other things that happen

at the level of metabolism and brown fat

in, let's say, the hours and day after a deliberate cold exposure?

As soon as you go in, of course, there's an activation,

but it seems like you're asking for the later outcomes

like blood pressure and stuff like that.

Is that what you mean?

Yeah, blood pressure, but also in terms of metabolism.

I know that in your study,

and we'll talk about brown fat in depth here in a moment,

but that there were changes to the brown fat

that equate to changes in, for instance,

people's ability to be comfortable in colder environments.

When they're not doing deliberate cold exposure.

Or in the same way that I can exercise on an exercise bike

or go out for a hard run,

but then if I go hiking with the family on Sunday

and it's a steep climb,

I could do that steep climb more easily

because I'm quote-unquote fit as a consequence of the exercise.

What are some of the fitness adaptations

of deliberate cold exposure?

Yeah, so what happens is that you get adapted a little bit

every time you go.

So you will like exercise, get a little bit stronger.

So every time you go into the cold water

for every time you will be more exposed to it,

you will feel more comfortable in the cold.

So you're gonna build your adaptation,

which happens on a metabolic level,

which is gonna be the brown fat.

So you will have more activation of your brown fat.

The mitochondria in the brown fat cells

are gonna be, you'll have more of those

and they will be more efficient at heating you up

because the body expects you to do this again.

So you are prepared in a way.

The capillaries in your skin will also become better

at like constricting.

So you will have a better shield of your body

to prepare you for the next time.

So you will become better at going into the cold water

in that way.

So the body makes these mechanisms

to changes your body in a way

so you can expose yourself to the next time, right?

And also you will have also your stress response

will also be subsided a bit.

So you will have a less increase

of your catecholamines with time.

With time also you will have because of this activation

of your brown fat or your muscles,

you will have an increase in your metabolism,

which will then make your insulin sensitivity better.

And this is shown in studies, for example,

there was this interesting study I found

just before I started my PhD,

which was from Giverstomer et al from 2016,

where they measured metabolism, not on brown fat,

but they measured insulin sensitivity

in middle-aged men and women

during one winter swimming season.

So they were not very young like they were in my study,

but they were middle-aged.

And I think this is very interesting.

So they, during these four or five months,

they were winter swimming,

they saw that they had a lower blood pressure

after the season and they had a lower heart rate.

And they also saw that they have a better insulin sensitivity.

And I think that is very interesting

because if you can have a better insulin sensitivity,

you can prevent lifestyle diseases.

So, and with lower blood pressure,

which is a very strong outcome also

for telling how much inflammation you have in the body.

And because it didn't measure a brown fat,

I figured that it could be, that was the missing link,

that was one of the explanations

to why we see this less inflammation in the body.

So the longer outcomes or the long-term outcomes

could be that you lower your blood pressure

and have a lower heart rate.

You also have a better insulin sensitivity

and a better glucose balance,

but that was shown, that is shown in my study.

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And we'll get back to the insulin sensitivity

and glucose balance.

That's an impressive list of benefits.

Blood pressure, of course, most people are aware

of blood pressure and what it is.

It's what they measure when we go to the doctor.

And it's not very sexy nowadays, you know,

blood pressure, people are like, oh, you know,

blood pressure, it's not, you know,

people want to hear about the inflammatory and the microbiome

and all of that stuff is really interesting.

But I think that blood pressure doesn't get enough attention.

And we have spoken to on this podcast to Dr. Peter Atia,

who is an expert in longevity and health span

and things of that sort.

And I was surprised to learn, again,

I shouldn't have been surprised

that the number one reason people die worldwide

is cerebral vascular disease and cardiovascular disease.

And there are basically three things on the list

of things to address.

One is not smoking or vaping, by the way, not smoking.

There are a few other things

related to blood markers, ApoB and things of that sort.

But then the big one is blood pressure.

And so it's interesting because we don't think

about blood pressure that much anymore

as the kind of people interested in health optimization

but blood pressure is so vital to control.

So it's wonderful to hear that deliberate cold exposure

is one way to control blood pressure.

I'm guessing in concert with other forms of exercise.

Let's talk about brown fat.

And if you're willing, I'd love to drill into brown fat

at a deep level.

Again, my understanding of this is far more elementary

than yours, obviously, you're the expert.

My understanding about brown fat

is that it's located in specific areas of our body,

maybe more widespread than when I learned in school.

I thought it was just at the clavicles

in the back of the neck and upper back,

but who knows, I learned that there's more of it

when we're children, maybe more distributed

throughout our body, and that it's rich in mitochondria.

But what is so special about the brown fat?

Like if we could just go into the biology

of brown fat a little bit, what does it look like?

You've measured it in human subjects.

Where is it distributed really?

Can it expand its distribution?

Can we activate and expand the amount of brown fat as adults?

And for those of you that are cringing already,

thinking we're talking about getting fatter,

it's quite the opposite.

We're talking about not subcutaneous fat,

but fat located around the organs.

But please educate me, tell me where I'm wrong

and expand my knowledge on brown fat.

Yeah, you are not wrong,

but it's true that there are more locations

of the brown fat than we previously thought.

There's this very nice study from 2017 by Leitner et al,

where they had made these Petsitees overlays

of their subjects, where you can see,

where in the body do we have brown fat?

And where can we grow more brown fat, so to say?

So the brown fat is very plastic,

so it means that it can grow and it can decrease.

And this is proven in studies where we have seen

people with a fair cryocytoma

is like a very specific cancer type.

Where from the 70s, where we can see

that if they have this specific kind of cancer type,

they have this tumor on the adrenal gland.

So they have like a huge increase in noreadrenaline.

And because of that,

they have this continuous activation of the brown fat.

And they have grown a lot of brown fat in the whole body,

abdomen or where it's located in these six different places,

but it is just like very much compared to normal people.

And what they then see,

what we learn from this study is that brown fat

can apparently grow if you have an increase

in noreadrenaline in the body.

It's not like you want that

because when that happens, you have a high blood pressure.

You don't want it chronically, right?

You just want it on like a short amount of time

and then it can grow for a bit,

but you don't want it chronically, of course not.

But because it activates also your sympathetic nervous system.

So they have also showed they had high blood pressure.

They had, they lost a lot of weight, of course,

because this is activating your metabolism.

So they found, luckily,

that when they removed this benign tumor,

that the brown fat decreases again to normal size.

And they gain weight again

and they had normal blood pressure.

So the story ends well,

but it's kind of like proof of concept

of the brown fat can actually grow.

So it's plastic in its way of like it can grow

and it can decrease again.

So that's very good.

Good studies to see what the body is capable of.

But we don't, of course, want all that brown fat.

We just want it to be,

we just want to keep it actually and keep it activated

because what we see in studies is also

that after the age of 40,

people, studies have shown that there is an association

with having less brown fat, but increase obesity.

So of course, we don't know yet

whether a brown fat decreases with ACE

and therefore we get obese or we get obese

and therefore we have less brown fat.

But as brown fat is an insulin-sensitive organ

in our body and we get obese,

just like the muscles get less insulin-sensitive,

the brown fat does as well.

And therefore it maybe decreases.

It could be a theory that I think could be

one of the reasons why we don't see

that much brown fat in elderly people.

Some have a lot, especially people working outside.

There are studies showing this.

People who do physical work outside,

farmers and interesting.

Yeah, they expose themselves to it.

So they'll just keep it in their way.

It's, and I suppose we should clarify for people

in case they don't know that insulin sensitivity

is a very good thing.

You want that.

You want yourselves to be sensitive to insulin.

Insulin insensitivity is type two diabetes

and is associated with obesity.

So just a point of clarification there.

Yeah, it's interesting to me.

I usually work out at home,

but I go to a gym once or twice a week if I can,

because it's good if I see the outside world.

And there are a few individuals at the gym

who are, they're not particularly large or muscular,

but they are incredibly lean and their posture is great,

presumably from the musculoskeletal work.

And they, they're in their 70s and 80s.

I mean, it's remarkable, right?

And I know all the telltale signs of hormone augmentation.

I'm very good at spotting that.

There are a few telltale signs.

I've talked about this on other podcasts.

And they're not, that's not why they're fit.

They're clearly of that look.

And you see this outside the gym too, of course,

for people that look like they've done a lot

of physical labor their whole life.

They're just moving a lot.

They have strong hands and features and they're,

and they're not necessarily excessively lean,

but you can tell that they've been using

their musculoskeletal system.

And I like to talk to these people and ask them like,

not what are you doing now for your workout,

but what did you grow up doing?

And I would say, and obviously I haven't run statistics

on this, but more than 75% of them respond

that they grew up on a farm,

or that they did some sort of manual labor

or were a postman or a postwoman

or doing something where they moved a lot

for their early years and throughout middle age.

And most of them are now in retirement,

but some of them are still working

and they all still moving a lot.

So the relationship between shiver and brown fat

makes sense to me.

But is it the case that as we're just moving around,

and I've heard of neat non-exercise induced thermogenesis.

So if we're just moving around

that we are activating brown fat,

or does there need to be this stressor?

Does there need to be shiver and a cold stimulus

or a heat stimulus to activate the brown fat?

In other words, is just staying active enough

or do we need to do some sort of temperature shock type thing

like deliberate cold exposure?

Yeah, I think that is a really good question

because how, also why do we have this tissue?

Then if it has to be extreme,

then you can question what do we need this tissue for?

But it seems that you can activate the brown fat

with just a little bit of exposure to cold.

So cold is the most potent stressor activator of our brown fat

because it's our temperature regulating organ in our body.

So first responder to that.

So the muscles will be a little bit too late

and therefore we have maybe these two kind of tissues.

So actually just exposing yourself or our hand actually

just to cold water.

So studies have shown that if you just put your hand in cold water,

not that you're going to gonna do that all day

or every day or anything,

it's not something you have to do,

but it just shows that you can activate your brown fat

just by getting a temperature change on your skin.

So you can go outside and tissue.

That's why also we were just talking about,

well, people who works outside or move a lot

or get in and out of it,

like changing the temperature of their body all the time.

They will have more brown fat

and activating that is gonna keep your metabolism higher

and your insulin sensitivity study have also shown this.

So the brown fat can be activated

as soon as you just change your temperature in the skin.

So going outside in a T-shirt wearing cooling vest,

also studies have shown this for 10 days.

It's gonna also grow your brown fat.

So you can get more brown fat

if you expose yourself to the cold.

You don't have to start in a cold shower.

You don't have to start in a cold plunge

if you're not really ready for that yet,

but just exposing yourself to the cold wind

has also shown to activate your brown fat.

Or if you don't wanna be like in this awake state,

then you can also just sleep in the cold

and you won't notice it that much maybe,

but studies have shown that if you sleep

in 19 degrees Celsius,

then you will activate your brown fat

and you will grow your brown fat.

So you have more of it.

So this very nice studies from Hansen et al from 2017 showed

that a group of subjects who slept in a room at 24 degrees

and then they made this PET CT scan to see

how much brown fat do they have from the beginning?

So what we call baseline.

Then they measured again after a month of sleeping in 19 degrees

and they saw, I think it's remarkable,

just one month at 19 degrees sleeping there.

They had a duvet on and they were still close on

when they're sleeping.

So they're under a cover, under a duvet?

Yeah, under a duvet.

The subjects were sleeping at 19 degrees for one month,

had increased insulin sensitivity.

The next month they stepped at 24 degrees,

they measured this again

and they had decreased actually a little bit

and then they stepped at 27 degrees.

So quite warm room actually for the fourth month

and they saw even less activation of the brown fat

and also insulin sensitivity.

So it seems that you can expose yourself

and pretty rapidly the brown fat will respond to this

because it's so sensitive to no adrenaline, right?

So if you keep exposing yourself to a little bit of cold,

you also get a little bit adapted to it

but that's because the brown fat

has grown these more mitochondria in the cells.

So these small energy fabrics

that's gonna activate the cells

and that's gonna take up glucose and fat

from the fatty acids from the bloodstream

to keep the thermogenesis up.

And that's gonna clear up some sugar

and it's gonna click in the bloodstream

and some fat as well.

So the brown fat can in that way decrease our unhealthy fat

which is the white fat.

And the white fat is what we don't want too much of

but we still need some of course.

And it's our energy storage.

So it's very important that it's there.

We just don't need a lot of it.

So on our thighs and also around our inner organs

that's where it's located.

So if we can have activation of the brown fat

just by going out in the cold

and just by sleeping in a cold room

or if you have courage for it,

you can go out and expose yourself in a cold plunge.

Cold showers is also gonna do the trick.

So you can do different variations of this

just exposing yourself to various temperatures

is gonna activate the brown fat

because it was involved to keep us in a perfect

homeostatic balance regarding temperature.

So to keep us alive.

Incredible.

I wanna just get a clarification

around this 19 degrees Celsius room that they're sleeping in.

So they're under a comforter duvet

and you mentioned they had clothes on.

The room is 19 degrees Celsius

but the temperature underneath their blanket

might not be 19 degrees Celsius.

So presumably it's the cold on their face

that's activating the increase in brown fat

that was observed.

Is that a reasonable expectation?

I think so, yeah.

Because you have so many co-receptors in your faces.

So actually it's enough.

And I think it corresponds very well

with the studies showing that you can activate the brown fat

just by putting a hand into a bucket of cold water.

And I did this experiment myself in my studies

just to see how well did they respond to cold water.

So it was four degrees Celsius cold water for four minutes.

And then I just measured blood pressure and heart rate

to see do they have like an activation of this.

I actually also measured the brown fat

during this cold exposure for four minutes

with an infrared thermography camera

to see can I see that the brown fat is activated.

And just to go back to the location of the brown fat.

So usually you cannot really see activation

of your brown fat

because it's located centrally

around your central nervous system.

And the biggest depot, as you mentioned before,

is up here under the clavicular bones.

So, and very close to the skin surface.

And because it's so close to the skin surface,

I could measure it with this very expensive camera.

And it's not very feasible for people to go home

and do this at home because it takes a lot of practice,

I can tell.

But we measured the brown fat with this.

And I could see that after a few minutes

that the activation was there

and increase in temperature arose from that activation

just four minutes.

So it's very rapid.

And I'm also measured in my study

how deep was the brown fat under your skin.

So it's very close to the surface,

which also shows that it needs to be there

to heat you up and heat your inner organs.

Well, I'm delighted to hear all of this.

And I'll tell you why.

One is by way of anecdote.

I mentioned a little bit earlier

that as an undergraduate,

I worked in a lab that studied thermogenesis

and we were doing that in animals,

but we had this room that was very cold.

The whole room was cold.

The guy who I worked for at the time,

kind of Harry Carlisle is a very accomplished physiologist.

He came from this lineage.

I don't know if this literature is still discussed much,

but it's a beautiful literature from Rothwell and stock.

They were the ones who discovered

non-exercise induced thermogenesis.

The fact that people bounce,

who bounce their legs a lot and move around a lot

and have a lot of kind of stochastic movement burn

up to 1,800 calories more per day

than people who sit more still.

Fascinating.

Incredible, just incredible.

I don't think that gets as much attention

as it deserves, publishing journals like Nature,

so very fine journals.

But in any event, one of the things that I noticed

when I started working in that laboratory

was that I was cold because the room was cold.

And Dr. Carlisle, Harry said,

well, the key is to wear a t-shirt in here

for about two or three days, and then you will cold adapt.

I thought, well, wouldn't I want to put on a hoodie

and get warm in there?

So I was comfortable.

And he said, no, actually what you want to do

is get yourself uncomfortably cold,

activate your brown fat.

And indeed, when I did that,

I think it was just two days of being

in that cold environment.

Then I could come back on the third day

and be perfectly comfortable

because the brown fat had expanded

or added mitochondria or both.

And I was perfectly comfortable in that environment.

I also got very, very lean in those days and weeks.

Now, I've never been somebody who's very lean,

nor am I somebody who carries a lot of excess adipose tissue.

I'm kind of somewhere in the middle.

I'm sure I could adjust that with feeding if I want to.

But it was striking what a powerful effect it had

on my entire system of thermal regulation.

And one of the things that I also delighted in

when Cell Reports Medicine published your study

is they had an accompanying press release

that went out to those of us that received press releases.

And it described a saying in Scandinavia,

which is essentially, I'm not going to attempt

to speak Danish, even though I have,

much of my family is in Denmark, believe it or not,

from Denmark.

We have a lot of Danes in my family.

I won't embarrass myself by trying to speak Danish

as I did before the microphones were rolling.

But that there's a saying that I think essentially

that translates to in the fall,

when you're approaching winter,

you want to actually wear fewer layers,

not bundle up when you go outside

so that you can prepare yourself for the cold of winter

and be able to heat yourself up using your brown fat.

And that in the spring, as the temperatures are warming,

rather than removing layers,

you want to wear more layers in order to be

a little bit uncomfortably warm

so that in the heat of the summer,

you're better at cooling your body.

Do I have that right?

Maybe, do you know the saying

and would you be willing to share it?

Only the Swedes and Danes will be able to understand.

Maybe the Norwegians too.

If you don't know it, that's okay.

Yeah, so I know the concept of it,

because we say it, you should wear less before winter

and more before summer.

Well, there it is in English,

so it doesn't have to be esoteric, but okay.

Yeah, and you're completely right.

And I think this is just something

that we know in the Scandinavian countries.

I think that we intuitively know this,

but if we just go back a little bit in history,

I think that around the 1950s,

the Russian government went out and said,

well, we should do something about the tuberculosis,

pandemic or epidemic, the worst at this time.

So they wanted to have the people

be more resilient to the cold

and also increase our immune system.

So in Scandinavia and actually also in Russia,

we put our babies outside to sleep in the prom.

And that is like to also to get more resistance to the cold,

but also to increase our immune system.

And we still do that in Denmark.

So we...

Do you really?

Yeah, we do.

Babies are taken out in the cold?

In the snow, in frosty rain, everything.

My two boys have been sleeping out in winter,

at least their first many three, four, five years,

because it's like very good for them.

And they get a better immune system

and get resilient to the cold.

So they will have less colds.

And also they run around in a T-shirt when it's super cold

because they have activated all their brown fat.

I didn't understand at that time, I must say.

But I kind of like intuitively also knew

because we have inherited this way of doing things

with our culture.

So, and I have heard people coming from the U.S.

saying, Danes are crazy.

They put the babies outside in proms and leave them there.

And then they go inside and drink coffee on the cafe.

Well, I don't think Danes are crazy.

I adore the Danes.

They're amazing culture and people.

I'm so fortunate to have family members from Denmark.

But I did notice, so when we were in Copenhagen,

and I know we saw you there not long ago, that was June,

the water in the harbor was cold for,

even though the Pacific is close to here,

which is very cold, felt pretty cold,

but it was summertime-ish.

So people were in summertime mode, right?

T-shirts and shorts and things of that sort.

But it did strike me that people in Copenhagen

are dramatically fitter than they are in the United States.

I mean, first of all, everyone's bicycling everywhere.

Not many people wearing sunglasses,

so trying to extract as much photon energy

from the sun as possible, which I support,

as everyone knows, I'm a big fan of getting sun.

But also, when we did see swimmers,

they were swimming in this cold water,

and like it was nothing,

and the range and age of the swimmers was remarkable.

You saw the kind of fit triathlete-looking types,

but also young kids, like really young kids,

and then people probably in their, again,

their 70s, 80s, maybe even 90s, really remarkable,

vastly different than what you see

if you go to the ocean here in Los Angeles or elsewhere.

So yeah, you Scandinavians are onto something with this.

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I'd like to talk about your study.

If you could give us a little bit of the backdrop

about what motivated that study

and then walk us through what you did,

who the subjects were, what you had them do,

what you measured, and as much detail

as you would like to share,

because I think it's such an important,

even in fair to say landmark study,

because it also explored not just cold,

but sauna and the co-use of cold and sauna

as a way to probe metabolism and brown fat

and other markers as well.

And as you do this, I'm hoping at some point

that you might tell us some of the observations

that you might have made that interested you

that perhaps were not in the paper,

because that's one of the great benefits

of sitting across from somebody

who did the work in detail.

So if you could tell us about your study

and what you did and what you discovered.

Thank you for that question, Andrew.

I'd love to also explain a little bit what did we do

because when people read this kind of paper,

they just see the numbers.

They don't see what happened before that.

And human studies are very different from my study.

My study, you can do a knockout or something

and then everything is perfectly matched and controlled.

Doing human studies is very far different from that

because people are different even in the groups.

Yeah, but when I started this research in 2016,

I did not really know what the brown fat was.

So I started reading up on all this

and I was very interested in preventive medicine.

Also the studies that I did before brown fat

was also like very much in the preventive side,

like how can we, that was about something else,

but the sweet tooth and how can we lower our sweet tooth

and stuff like that.

But after that, I wanted to do something new.

So I looked into the brown fat,

got hired in this fantastic research group

where it's a cell group.

So they mostly did cell studies

and they didn't have anyone to do a human study yet.

But they really wanted me to do that.

So I read upon a lot of research

about how does the brown fat get activated,

what have been done already.

And I mentioned the paper before with the sleeping in the cold.

I found that particular paper very fascinating.

And that was also where at that time I was like,

okay, so cold exposure as an intervention

of sleeping in the cold could be a good thing

to go out and say, well, people do this.

But on the other hand, first of all, it was already done.

That was one thing.

But the other thing was like, well,

I wanted to see if we can do some kind of activity

so we can have people move also, go and do something,

do something together or whatever.

And the cold made us think about, well,

what about winter swimming?

And it was kind of like a bit of a joke in the beginning

is like winter swimming,

yeah, it's gonna activate the brown fat, right?

But when we read the literature,

we couldn't really find anything about activation

of the brown fat with cold water

besides hand in a bucket of cold water.

That really, there was already there.

So we were just thinking, okay,

so it should be very potent activation of the brown fat

if it's cold water, but very different from cold air.

So it was kind of also a new thing we were going into

and we knew that we were gonna do like a more of a proof

of concept study at the beginning of it

because it was like winter swimmers

must in theory activate the brown fat, right?

But we kind of didn't really know

was this kind of stress too much, too little

or what will happen actually.

But we had this idea about, well,

we always say that cold water and winter swimming

will activate your metabolism,

but do we know if it does that?

No, we don't.

And while this idea was a little bit fun at the beginning,

we kind of accepted it.

It was like, okay, let's just try this out.

But because we didn't have the funding for it,

we was like, okay, let's do a proof of concept study.

Let's go with a small number,

but enough to see a difference between the groups.

So the power calculation of that study is done

on what we know from PET CT scannings of the brown fat.

So that's the main outcome of that, of course.

So, and we wanted to go a little bit small

on the numbers of participants

because we wanted to dig a little bit deeper

into the different mechanisms

and also redo some of the days.

So I really wanted to do that

to see if I can replicate also the findings.

And that's gonna take a lot of funding,

but it's also gonna take a lot of time to do it.

So the proof of concept was just going small,

but looking at different mechanisms,

we also took fat biopsies, for example,

and looked at the white fat to see

if there was any differences between the groups

before and after and stuff like that.

So that's kind of like how it started.

And the first year was like a field study for me.

So I was not a winter swimmer when I started this.

It was just...

Oh, really?

No, I wasn't at all.

And I would say I was a bit afraid of the cold myself.

Bit of a cold sissy, always cold,

having big socks on and sweaters and stuff like that.

So I was like, I am so comfortable.

I'm just like everybody else, very comfortable.

I like being completely temperature neutral.

But I started like playing with this thought,

like, well, if this is so healthy in theory,

I should not pack myself up.

I should start not doing that.

Yeah, but the first year,

observation of winter swimmers on the jetty,

they kind of joked about it.

They say, come on, you need to try this.

You cannot study this unless you have tried it.

And I was like, ha, ha, very funny.

Of course I can do that, but I couldn't.

I read the literature, I understood in theory

what happens when you go into cold water.

But I completely understood it when I first tried it.

The first few times, not so funny, it felt painful.

It was just like running too long after a long break

and your muscles hurt the day after, right?

You completely regret that you took that extra mile.

What about when you say uncomfortable,

you mean uncomfortable when you got in

and when you were in or uncomfortable afterwards?

Because I find that on rare occasions,

well, I should just, full disclosure,

I do deliberate cold exposure every morning

for about a minute to two minutes in a cold plunge.

There are days that I miss, but when I'm at home,

I do that, and when I travel, I do a cold shower.

I do finish with a warm shower.

So, and we'll talk about why that's probably

not the best idea.

But, and I've been doing it for some years now on and off,

but so just full disclosure, I'm a devotee

and I have family members that hate the cold

but have gotten into it and are starting to like it.

But they don't, and I don't necessarily

like the experience in the cold water,

but I love the way I feel when I get out.

And I'm a hundred percent on that statement

about loving it when I get out.

Occasionally, it feels good to be in there,

it feels invigorating, and I think I've learned

to control the gas reflex and the hyperventilation,

and I just have told myself what we know,

which is that the forebrain struggles to engage

for the first 20 or 30 seconds,

but if you can get past that wall,

it's far easier to push through.

But when you say that it was really uncomfortable,

do you mean the experience of getting in

or you also felt lousy afterward?

Yeah, and very important to clear that out.

I only felt very uncomfortable doing it at the moment,

but afterwards, the first time I went with a group,

and actually my husband was as well,

because I really wanted someone I knew coming alone

because it's very normal

if you haven't done this before,

you feel a little bit anxious about it.

This is Jonin's studies as well,

because blood pressure and heart rate goes up

in those who are new to this kind of activity.

So I was a little bit anxious about it.

So it was really uncomfortable just doing it,

but afterwards, as soon as I got up, I felt fantastic.

And we went into the sauna and I did three rounds

because I just loved it.

I loved the feeling afterwards

because you have all these new transmitters

going in your brain and you feel more positive,

I feel invigorated, I had so much energy,

and I could totally see why people would do this

to get energy throughout the day

because I definitely had that.

I didn't have to do three dips to get that.

I think one would be enough,

and I often do that also now today.

I do one dip, sometimes I do two or three dips

in one round, you can say in one day,

but often it's like just one or two times a week.

For me, that is enough to get that energy

and to get that positive feeling.

And I think that that is also why I put up my study

in that way.

I wanted to study the lowest dose, you can say,

the lowest amount that we can get away with,

but still see health benefits.

So what I observed there on the jetty

was that some did it a long time.

They were in the water for a very long time.

And to me, it seemed maybe a little bit extreme.

Could you give me an example of a long time?

Well, so maybe they were really swimming

and they could be 20 minutes or half an hour.

That's a long time.

That's a long time, and there was ice

and people who came up.

I mean, I just didn't really feel that this is something

that I wanted to go out and recommend to people

after my PhD.

You didn't want any of your research subjects dying either

because if you're not adapted,

I mean, people can do that.

Also a 20 minute cold shower or 20 minute cold plunge.

I know people do it, but it's probably not a good idea.

No, probably not.

It's gonna exhaust yourselves and make them age too fast.

So exactly that's, when you pass that hermetic stress,

the healthy stress level,

that's what is happening.

The quite opposite is almost chronic stress

actually in the cells.

Well, what happened then was that I found out

that if I want to have this protocol

get through ethical committee,

I really needed to go very sleek with the not too long

and make sure that they were also very healthy

and to get approval, of course, of this study.

But what I did was to recruit winter swimmers

who already have been swimming for two or three seasons.

And I just observed them.

I said, I'm not gonna do an intervention study yet.

I did that after, but I wanted to do a proof of concept

where they were already adapted to the cold

and then compare them to a matched control group

who were matched on, you can say diet.

So were they vegetarian or not?

And one of them was in each group also.

They weren't all vegetarians.

No, no, no.

Just one in each group, yeah.

I was gonna say with all the amazing fish and meat

in Denmark, I'd have a hard time being a vegetarian.

The breads are amazing, the fruits and vegetables too,

but okay, so there were a couple of vegetarians

in each group.

Yeah, one in each, yeah.

And they were matched on-

I have family members who are vegetarians,

so I'm just poking fun.

Yeah, but they were matched on different things.

So what we usually match the monitor is also BMI.

We chose one gender in this study

and we would always choose both men and women normally,

but we do see that there are different brown fat levels

depending on gender.

So women have more brown fat than men.

Really?

Hmm, interesting.

Yeah, I think it's interesting.

That deserves study.

Yeah, why actually?

I think it's interesting because women are also smaller,

so in size and mass, right?

But they also have a lower peripheral temperature,

especially on hands and ears and...

Is that right?

That's documented that women do run colder than men?

Yeah, and there's also...

Physiologically, I didn't say psychologically.

No, no, no.

We won't go to the psychological cold heat, yeah.

That's different.

That's a different podcast.

Yeah.

Another time.

So women are just colder physically,

so on hands and ears, it's measured on that,

and feet as well.

So compared to men.

And men have bigger hearts than women

and they can pump out more blood peripheral

than in a woman's body.

So that could be an explanation for the colder hands,

for example.

Thermocomfortable state is also different between genders.

So men are more comfortable at 22 degrees Celsius

and women are thermocomfortable at 24 degrees Celsius.

And this is...

So the thermostat wars of home have been now validated.

Yes.

Okay.

Two degrees Celsius.

By the way, prior to starting recording,

I made the executive decision that we were gonna go

with Celsius throughout the podcast

because the majority of the world uses Celsius.

So for those of you that think in Fahrenheit,

the internet is your friend in making those conversions.

So we're sticking with Celsius.

So men tend to be thermocomfortable

at 22 degrees Celsius, women at 24.

Okay, interesting.

Explains a lot about like, oh, so some arguments

in the homes where men are turning down the heater

and women are turning up the heater and they cannot really...

So it's really, I'm on both sides here.

I understand the men, we understand the women,

there is a difference there,

which was also one of the reasons why we had,

we in this proof of concept study chose one gender.

So it is not like only because we wanted to study men,

it was just to see, to eliminate all the confounding factors

which could have an impact on our results.

So that was one of the reasons.

But also because we, yeah,

so women have more brown fat than men,

otherwise we would have to like do four groups

or something like that and not having funding yet.

We were like, okay, we need to do like just one group,

just a control group and then a group

who were already winter swimmers.

So I recruited winter swimmers who have been swimming

for two to three seasons

because I wanted them to be already adapted

but not going too long in the water.

So they told me, I did a lot of screening here,

of course beforehand and interviews

to see, to ask them how much do you do

and how long do you stay in the water?

And I monitored how long did they then stay in the water

and recruited based on that they only did

like two to three times per week.

It seems reasonable for Denmark at least to do that.

And they stayed only in the water for one to two minutes.

So the course subsides very quickly

and you will get this activation of your

rest and digest system,

which is your parasympathetic nervous system.

So the other branch of your autonomous nervous system.

And you get that activation

because you submerge into cold water.

And when you do that,

you have an activation of your diving response

and that's gonna slow down the,

you can say the consumption of oxygen also in your body

and that's gonna slow down your heart rate.

Could I pause you on this?

Cause I've heard this before

that when we get into cold water,

shower or immersion,

we get this sympathetic autonomic response.

So increased blood pressure, increased heart rate,

release of norepinephrine

from the locus ceruleus in the brain,

release of adrenaline, dopamine,

adrenaline from the, from the adrenals,

dopamine presumably within the brain,

but that the parasympathetic response is activated

when we put our face into cold water or go underwater.

And that's a calming relaxation response.

So this brings us back to,

I don't wanna take us off track

from you describing the study,

but this brings us back to the first question,

which is if I go completely underwater for a moment

when I start my cold plunge,

does that change the physiological outcome

as compared to if I just submerge myself up to the neck?

And that, and actually nowadays there's,

it seems to be a little bit of a movement online

of people putting a bowl of ice water on their countertop

and submerging their face into it.

Did you see this?

Sorry, I was seeing more and more posts about this.

So can you just touch on what the dive reflex is

and why it perhaps activates the parasympathetic response,

this calming response?

Well, so the diving reflex is activated

when you submerge into cold water.

Even just to the neck?

Yeah.

Or I thought you had to get your face under.

I'm not arguing different.

You're the expert, I just wanna, yeah.

I haven't really, I haven't read that.

I've just seen that you can activate your diving response

as soon as you go underwater with your body.

So you don't have to do it with your face.

As far as I understand, I could be wrong though, yeah.

So when you activate your diving response,

you will slow down your oxygen consumption in your body.

And that is because the body tries to preserve oxygen,

so you will not get hypothermic too fast.

So it's kind of like a survival system in your body.

So this survival system is very important for us, of course.

So that will be activated.

And because of that, you will have to maybe one minute or so,

that can be precise on that

because maybe also varies a bit in humans.

So one to two minutes,

you will have full activation of the sympathetic nervous system

but also the parasympathetic nervous system.

And that's gonna activate, for example,

something like serotonin in your brain,

which is also good for mental balance

and people feeling in mental balance afterwards,

after they go up.

So that is measured on a questionnaires

and also measured on anecdotes.

Of course, people tell all the time

that they feel good afterwards.

We need studies on this.

So if anyone's sitting out there thinking that's interesting,

then please do some studies on that

to get more out on that.

So you observed these winter swimmers

who have done this for a few seasons.

They're coming around for a new season of winter swimming

and you've decided to recruit them as subjects.

They are getting into cold water,

climbing down a ladder or jumping into the water

up to their neck.

Okay, climbing down a ladder into the,

because this is done outdoors.

What a fun study to do.

My graduate thesis was done under fluorescent lights

with no windows in a building that,

I mean, I had a ton of fun as a PhD student.

I actually lived in the laboratory as a PhD student.

I loved it so much,

but not something required to do a PhD, by the way.

But they're climbing down the ladder,

getting in up to their neck,

staying in for one to two minutes,

and then getting out.

And how many times a week are they doing this?

So they do this two to three times per week.

And for each time they go, each day they go,

they take three rounds of,

so three dips and two sauna sessions.

So they start in the cold and they end in the cold water.

Okay, so it's get in for one to two minutes,

then get out and get into the sauna.

What is the temperature of the sauna?

About 80 degrees Celsius.

Okay, then how long are they in the sauna?

So they stayed there for 10 to 15 minutes.

So depending on if they went two times per week

or three times per week.

Okay, and then they get back into the cold

for a few minutes, two minutes.

Up to two minutes, yeah.

Okay, then back into the sauna, 15 minutes or so.

Then back into the cold for a third round,

back into the sauna, and then they're-

Ending on the cold.

And then back into the cold again,

and then ending on cold.

And we will talk about why it's important to end on cold,

the so-called sober principle.

How cold was the water in this particular,

given the average,

because I realized it's outdoor winter swimming.

So it's gonna vary depending on wind chill

and things as well.

Of course, so it's a very uncontrolled environment

to do this kind of study then.

But I wanted to do something

that was also very close to something people can do for free,

going out in nature and use that

and also have the nature-like,

it's a very healthy impact on us.

It lowers our stress level as well.

So by doing so, I also measured the temperature

every time they went.

So I have this graph,

and it's actually in the winter swimming book.

It shows the temperature in Denmark

going from October to April.

And it starts at 12 degrees.

I think it's around 12 degrees Celsius in the water.

And then it goes down to two degrees

and on average in January and then up again.

So it's within the spectrum of very cold water,

I would say from around 15 degrees Celsius and down.

But it was actually not colder

than two to four degrees on average when it was the coldest.

So it doesn't have to be that cold to be good enough

and enough to activate our metabolism.

And what time of day are the participants doing

this cold sauna alternation?

So I think they did this throughout the day.

So I didn't control whether they wanted to go

in the morning and the afternoon or in the evening.

At that time where I set up this study,

I was not controlling it in that way.

I wanted them to go whenever they had time.

And I also think that is the most important message

to give to people is when do it when you have time.

It's not, if doing it when you get home from work

and it's six o'clock in the evening

and this is the time where you can do it,

then try out if it's gonna impact your sleep or not.

If it doesn't impact your sleep, then fine.

But you have to try for yourself

and find out what works for you.

It's the same for coffee, for example, right?

Some people can drink coffee in the evening

and go to bed and they can sleep.

I can't.

Or exercise.

Or exercise, exactly.

So I can't do that.

And that's because the coffee, exercise, cold water,

immersion, it's gonna activate your sympathetic nervous system.

You have an increase in stress response in your body

and that's gonna make it really hard to fall asleep

for some people at least.

Maybe you are super exhausted anyways

and then you will just crash anyways, but yeah.

But that's the only thing.

So I just told them to do this if they can during the daytime

and that's primarily what they also did.

And then all along you're measuring brown fat

by way of this infrared camera, right?

So what did you observe in terms of changes in brown fat?

How quickly did that occur?

And then I'd like to ask also about sauna a bit more

because earlier you mentioned that you can activate

brown fat with sauna as well, with heat.

Oh, with heat, yeah.

Surface of the skin.

How long did it take before you observed

significant increases in brown fat?

And was it increased density of brown fat or distribution?

Was it showing expansion to different regions

throughout the body?

And maybe you could also touch on some of the changes

in insulin sensitivity and metabolism.

Yeah, a very good question.

And I didn't mention this before,

but besides measuring temperature

as an outcome for brown fat activity,

we also did PET MRI scanning of the brown fat.

So this is like the golden standard for measuring brown fat.

And it's not very feasible for normal people to get

and a PET CT or PET MRI scanning of the brown fat

is super expensive.

So we had both to see if we could have like a continuous measure

of brown fat in humans,

because that was already not out there.

So I wanted to see during both the experimental days,

but also during day and night,

what kind of like circadian rhythm

do we have in our brown fat activity?

So that's why I wanted to have that as well.

So the PET CT scanning or the PET MRI scanning

was to see upon code activation stimulation for some hours.

Do we have activation?

Can we see the brown fat in this subject?

And also during thermonutrality or thermocomfortable state,

how is that activated in each of the group, of course?

So you want to see how comfortable people were

away from the cold water and sauna,

just at different temperature environments.

Is that right?

Yes, I also measured that.

How comfortable are you?

I made this scale like visual analog scale

and asked them,

how comfortable do you feel with this temperature?

And throughout the study days,

during cold exposure and thermocomfortable day,

I had a whole day where I just kept them thermocomfortable,

to see do they activate the brown fat

if they're just completely thermocomfortable,

as good as we could get with that,

because we were asking people on a scale from one to 10

and five being thermocomfortable,

where are you on the scales of one would be very cold

and 10 would be super burning hot.

Yeah, and so that was a way to try to figure out

how do they actually feel also during the studies.

I also measured in electromyography of muscles

to see do they shiver during the cooling day.

Sometimes people shiver before they know

they're really shivering, so I had this.

Interesting, so it's our conscious perception

of shivering might not be the best readout of shiver.

Yeah, well, if you also get adapted to the cold water,

you will have less shivering, there will be less vigorous,

there will be very small,

so you wouldn't probably know that you are shivering

because the shivering is so small

and the mitochondria in the muscle cells will be so dense

that it doesn't need to shiver maybe that much

to get the thermogenesis going,

compared to when you're completely new,

to cold water exposure and you're not adapted,

then the body needs to create these mitochondria,

these energy fabrics to keep you warm

and that's also what the exercise is in the beginning.

But when we measured this,

we did see that the winter swimmers were shivering less

or having less vigorous shivering when they said, I'm cold.

So even though their perception of the cold

was pretty similar in the groups,

we could see that the activation of the muscles

that we measured on were different

and more vigorous in the control group.

Were the subjects incentivized to be in the study?

Were they paid or anything of that sort?

Or did they just happen to like doing cold and sauna?

And so that's why they did the study.

Well, they got paid a little bit for it, but not much

and that's how we do the studies.

Sure, I was just curious.

Yeah, I was just curious.

There might be some folks that wonder.

So what did you discover in terms of changes

in brown fat, insulin resistance,

or insulin sensitivity rather, and metabolism?

So what we saw was we had these kind of different measures

to see what's actually going on

when they are already adapted to the cold water

compared to a control group

who was matched on various parameters.

We did see that the winter swimmers

had an increased insulin sensitivity.

They produced less insulin on all the experimental days.

So besides from just cooling them

and measuring the brown fat on each of these cooling days,

there were two cooling days

and one thermocomfortable day, right?

So I wanted to measure insulin when they were just,

they were fasting, meaning that they hadn't eaten

in eight hours before the study day.

And they were completely laying still,

not moving just in a bed.

And we measured insulin during the experimental day

just to see what level are they on.

And we could see that the winter swimmer

had lower production of insulin.

And they also, when they had glucose strength,

so we give them that to see if they,

to test before we enroll them in studies,

to see if they have diabetes, for example,

and not knowing, for example,

that would ruin maybe the study.

So we test for that and see if they have a normal curve.

So what we did see in that was

the winter swimmers had faster glucose clearance

in the bloodstream.

So after two hours, we could see that they had a lower level

and the curve went down faster than in the control group.

So despite having lower insulin release,

they have better blood glucose clearance,

which is really what we all seek, right?

Excessive insulin is bad.

Insulin being a more or less a chaperone for blood glucose.

We can do all sorts of other things as well, of course,

but, and having high blood glucose, obviously,

terrible for cells, especially brain cells.

I don't think people realize how toxic high blood glucose is.

Having high glucose is sort of,

if you want to kill neurons,

you make, you make their,

put them in an environment where there's too much sugar.

Oh, yeah, very, yeah, very neurotoxic.

I mean, that's, and there are mechanisms like insulin

that buffer that, we keep, you know,

keeping blood glucose in a reasonable range

so that that doesn't happen.

I mean, I think that's why people will go

into insulinemic shock.

Hypoglycemic shock is also possible.

So that range in which neurons are happy

is not a tremendously large range.

Incidentally, the range in which neurons are happy

and surviving is much greater as one gets colder

than when you heat up.

I mean, you can basically destroy brain cells

by getting too hot for too long.

Oh, yeah, yeah.

You can definitely destroy brain cells permanently

by getting too cold for too long,

but you have to get really, really cold

for a really long time.

Yeah, yeah.

Very interesting.

Yeah, we were thinking about doing an episode

on survival of the brain after death kind of things

which actually happens.

You know, you hear about these people

who are declared dead and then come back,

and there's actually now a lot of cryopreservation type

approaches for that.

This is, anyway, we risk going into the esoteric now.

So we'll steer us back to our discussion about your study.

But so if I do the math, these subjects are in the cold.

Let's say they're doing three rounds of cold

for one to two minutes, two or three times a week.

What were the thresholds that you discovered

were important for getting these positive changes

in such as reduced blood sugar

or clearance of blood sugar being more efficient,

reduced insulin, improved brown fat distribution

and density.

How much cold exposure do people need?

How much heat exposure do people need

in order to extract these benefits?

Yeah, so when we then calculated the numbers together,

we could see that this was ended up being 11 minutes

in total per week.

So not in one session, of course,

but they had two to three visits

to the water and the sauna per week.

So when we divide that out,

it corresponds to being in cold water

one to two minutes at a time,

but also in the sauna 10 to 15 minutes at a time.

And I think this is very like,

also similar to what we see in other studies

when we look, for example, to the observational studies

from the Finnish cohort study from Laok and et al.

For example, they published this very amazing paper

in 2015, some results from this long course study

where they show that up to 30 minutes in the sauna

was healthy and you lower your risk of cardiovascular disease.

And that's like the threshold.

And if you go further than that,

then there is not more healthy benefits to gain from that.

So, and before that, it's like 19 minutes,

then you will have this dose-response relationship

up to 19 minutes,

that's really in decreasing your risk

of cardiovascular diseases.

And I think we really-

That's per week, 90 minutes per week.

90 minutes per session now.

Per session.

Yeah, per session.

If we then compare that with my study

which was 10 to 15 minutes per session,

then I think it fits very well

with what we call the hermetic stress or healthy stress

where you expose the cells to this kind of like

potent, very stressful situation

where they increase heat shock proteins in the cells

and that will repair the cells.

But if you then overdo it

and you go beyond the maybe 30 minutes in the sauna,

this observational study from Finland

with more than up to 2000 sauna bathers

where they follow these for 20 years,

they see that 30 minutes per session is like enough.

And if you go above that,

you don't get more health benefits out of it.

So I think there's a window where we can say

the healthy stress corresponds to like 10 minutes.

And I think it's like-

Per session.

Per session.

And it's not much actually.

So you don't need to,

it shows that you don't have to expose yourself

very much to the heat

or very much actually to the cold

to get this healthy benefits from going into cold,

going to heat and have healthy benefits

on your cardiovascular system.

So I think this is very important,

also message to get out

that you don't have to go extreme.

You don't have to swim for a half an hour in the cold water.

You can go in the water for one to two minutes per session

but go up to 11 minutes per week in total.

And for the sauna, my study showed 57 minutes

in total per week.

And if we also then divided out on these two to three days

and two sessions each day correspond to 10 to 15 minutes.

So it's a low stress whole,

but I think it's good to have that

to maybe we can aim for that

if people need to have something to aim for.

And I think it's really good to have that

because then you don't overdo it.

And if you overdo it, you exhaust the cells

and that will increase your risk

of cardiovascular disease also.

So.

Well, I get a lot of questions about this

and I did solicit for questions for this podcast on Twitter.

And one of the questions that I got was

as one becomes more cold adapted,

do the benefits start to wear off

or can people do too much cold exposure?

And of course the answer to that is yes,

you can become hypothermic,

but I'm sensing a different answer now,

which is if I understand correctly,

the threshold is 11 minutes total

per week of deliberate cold exposure

divided into two or three sessions

of maybe one to three minutes

depending on how long somebody stays in.

And then 57 minutes,

I want to be careful not to round up to an hour,

but divided into maybe three 20 minute sessions or so.

So one doesn't have to be perfect

as long as you get beyond that threshold.

But I wonder something which is,

is it the case that if somebody said,

oh, I'm just going to do one 11 minute session per week,

that might actually not be as beneficial as dividing it up

because what you told us earlier

is that the hermetic response

depends on having that cold shock.

You actually don't want to become too cold adapted.

I mean, once the blood pressure response drops down,

so in minute four, five, and six,

you're getting very cold and you're shivering,

but one is not getting the autonomic stimulus that they want.

I guess I could liken this to,

if exercise worked in a way

where it was only the first few minutes of exercise

that really triggered the adaptation,

of course this is not how it works,

but in fact, probably quite the opposite.

But if that were the case,

then it's not simply the total amount of exercise,

but dividing up the sessions into little bouts

where every single time it acts as a stimulus,

that seems to be the key here.

This is very important

because having watched the landscape of this on social media,

but also in books and generally,

I think you're the first person to really touch on this,

that the goal is not to get so cold adapted

that you can sit in for the full 11 minutes in one session,

where the goal isn't to be able to do an hour

of very hot sauna, if you want to,

I suppose people could do it for other reasons,

but if the goal is to improve these health metrics,

then the idea is to keep the stimulus a stimulus.

Short, exactly, yeah.

Great, well, this also,

I think there's practical feasibility as you pointed out

because getting into a cold shower or cold immersion

or natural body water for a couple of minutes

is far less challenging to most people

than finding a full morning to go spend there,

but I've never really heard it articulated

that the longer sessions might not be beneficial

and might actually be detrimental.

That's very important.

Were there any other observations that you made

that did not make it into the paper

or that were kind of in the margin notes,

in terms of psychological benefits or anything of that sort?

There was this recent study on soldiers

that talked about weight loss,

it's sort of a controversial study for a lot of reasons,

but one of the things they remarked in the paper

was that there were a lot of psychological changes,

improved buffering against anxiety.

They even, the men and women in that study reported,

one of the significant effects

was significantly improved sexual satisfaction.

They didn't tell us what that meant for these subjects,

but as we won't go there,

but a number of subjective improvements.

Was there anything that you observed or took note of

in your study that perhaps didn't make the main abstract

but that we should be aware of?

Yeah, there were some.

And today I regret that I didn't measure on sleep,

for example.

I frankly didn't really think about that

when I designed the study.

So we were very much occupied with the metabolism

and kind of had the thought,

maybe this could impact sleep quality.

And I wish I just had the thought

that why don't you just ask them in a questionnaire?

But I asked them every morning,

or everyone who's not many mornings

to just two mornings actually, we measured on,

but the winter swimmers told us before I wrote them

that they had a really good sleep quality.

The control group also had that,

but they told me on the day

where we measured brown fat on a day and a night.

So actually two days and two nights,

they told me that they had a good night's sleep,

but they also woke up.

So it's just telling me

that they also had like a quick wake up

and then they fell asleep again.

And the winter swimmers told that they have a really good sleep.

So it's like, in general,

they also say we sleep very well, I sleep very well.

So it's anecdotally general,

it corresponds to what I heard in my study,

but nothing that I measured on,

which could be fun to do in the future,

but we didn't measure on sleep quality.

That would have been a really good idea to do.

They also told me that they were very comfortable

when they were cold.

They don't mind winter swimmers,

they don't mind going out, for example,

in the cold with a T-shirt.

They were also less scared of showing their skin.

That was also one observation.

Interesting.

So kind of a reduced social anxiety.

Yeah, they were just so comfortable in the lab,

as you just mentioned before,

coats on and everybody was joining around.

It was very busy and all the other scientists

out in the hallway.

And also my supervisor had her office down the hallway

and one of the winter swimmers one day

just got out of bed after having been in the study

for eight hours, it was a long day, right?

He jumped out of the bed

and had his clothes in the bathroom

and he went out completely naked.

He didn't care.

He just went out, it was like, oh.

So that's a side effect perhaps

of getting too comfortable with the cold.

We're not recommending that.

Although in your book you dedicated some,

let me start that again,

although in your book you dedicated some pages

to naked winter swimming

or I should say naked cold water exposure

as opposed to with bathing suit.

Are there any data on this?

I'm sorry, chuckling,

but I think in most places in the United States

skinny dipping is not legal, most public beaches.

There are a few.

In fact, where my laboratory

before moving to Stanford was in San Diego

and at the Salk Institute for Biological Studies,

beautiful building, incredible science is done there.

The beach right below that is called Blacks Beach.

Okay.

And it's a known nude beach.

And so whenever tourists were heading down the stairway there,

I would sort of let them know,

especially if they had kids, I'd let them know.

And it's a nude beach of a particular genre.

So I'd give them a little warning

about what they could expect down below.

In any event, those beaches are quite rare

in the United States, maybe compared to Europe,

I don't know.

But yeah, so is there anything special

about clothes lists versus clothes exposure?

Yeah, I think in that sense we are a bit more free

with this kind of like,

but remember we also had this winter swimming culture

for hundreds of years in Denmark.

And the oldest winter swimming clubs that we have,

especially the one we have in Copenhagen

where I did my next study, which we haven't talked about,

but and it's also not published yet.

But in that winter swimming club,

it's the oldest one we have and it's huge.

And they swim naked at this facility.

Men and women.

Men and women.

And they have sauna where they can go in together.

And they also have the separate saunas.

But it's very much a Danish thing.

And I think it's good if people want that.

And I had it in my book because people want to know

if they have to swim with their bathing suit on

or if they can take it off or what's the difference?

Is there any difference in this?

And if you ask me, there is no difference.

If you have your little skinny bikini on,

it's not gonna do any difference to your cold exposure

or your adaptation.

It's not gonna do any difference.

Your benefits, of course.

But I think that it has something else.

It has something to do with how you also observe yourself,

how you observe your surroundings.

And it's some sense of freedom in skinny dipping.

So I think people in Denmark who does this is,

they do the winter swimming because they feel free

when they do this.

They come home from work.

They go to this club and they skinny dip

and they feel like in touch with nature.

And they have maybe done this their whole life.

So this is an old tradition in Denmark,

in some of the clubs,

but the newer clubs that are coming,

they don't do a skinny dip.

So everyone has bathing suit on.

I never skinny dip because there are people around,

people with phones and taking pictures all the time.

So this-

It's a different nowadays, everything's recorded.

Yeah.

And also this old tradition is also fading away

because of that.

Yeah, I use sauna and cold at home,

but when I travel, there's a banya.

So Russian banya has hot sauna and cold plunge.

There's one in San Francisco called Archimedes banya.

And that one is clothing optional.

So some people are clothed such as myself

and then other people are not.

And it's co-ed most of the time.

I think they have a female separated evenings

or something like that.

And then the other banya is Spa 88,

which is on Wall Street in New York

is an amazing banya as well.

And these are starting to crop up in different cities

or maybe they've been there for a long time

and as deliberate cold exposure in sauna gets more popular,

more people are using them.

The one in New York that that Spa 88 is always clothed.

And it's interesting because people hear naked

or skinny dipping and they might get certain ideas in mind.

It, all these places are very well lit

and they all have a tone of kind of health

that is about the kind of health and wellness.

I guess the point being that there's no requirement

to do one thing or the other.

Although in the studies that you did,

obviously people were clothed.

But I did pay attention to those pages in your book.

I thought it's interesting that you put some

dedicated passages in your book related to this.

And I think it-

My publisher wanted that.

Oh, your publisher wanted that.

Interesting.

Yeah, it was not me.

It was like my publisher really wanted

to have a little discussion about that.

So I was like, okay.

Well, I think it points to a larger theme,

which is I think for a lot of people

who already do these practices, there's no shock there.

For people that do not do deliberate cold exposure

or sauna, I think that there is this idea perhaps

that, oh, these are traditions that are kind of fringe

or that they're kind of-

And I just, I wanna cue that point

because there's so many things that are happening right now

in biomedical research and medicine.

Serious quality peer reviewed studies

published in excellent journals like your paper

on things like deliberate cold exposure, sauna,

the use of particular supplements,

natural herbs and supplements.

I mean, there's an entire branch

of the National Institutes of Health in the United States

dedicated just to the study of supplements

and behavioral interventions for health

like meditation and breath work.

Really incredible.

It's really incredible.

And psychedelics, of course, being something

that for a long time was part of a certain community

and feel and now is being, frankly,

adopted by mainstream medicine, even pharma.

So the times are changing.

And so, yes, I think it's important to know

that it's perfectly acceptable

and encouraged to wear clothing.

So-

Absolutely, absolutely, yeah.

And one other thing that I wanted to mention

going back to your questions around with,

there were any observations in the studies

which we really maybe haven't discussed yet

and maybe it's in the back of the paper

and not mentioned that much was,

one of the winter swimmers didn't have any brown fat

when we measured him.

Zero.

Zero.

And we do see this in previous studies as well

that some humans don't have any brown fat.

Did he carry a lot of white fat adipose tissue?

Was he obese?

No, he wasn't.

No, he was not obese

because that he would not have been in the study then.

Oh, right, yes, you mentioned this earlier.

Forgive me.

No, no, it's fine.

But what I did observe before I knew

that he didn't have any brown fat was that

during the cooling experiment

where I cooled him for two hours

before they go into the PET CT scanner,

he was not able to control his shivering

like the winter swimmers could.

So he got very cold very easily

compared to the others.

So, and without, I didn't know what was different about him

but we could, all of me and the three others

were working on the experiment.

We were like, okay, what's going on?

Because we turned down the temperature

but he started like shivering

and then we had to turn it up again.

And it was just all over the place, the temperature.

It's not, it wasn't that controlled like the others.

It was pretty similar protocol.

I could just do pretty much the same

because they were same size and also same gender.

So it was easier to foresee what was gonna happen

and when will they start shivering?

I quickly learned that.

But with this subject, it was just,

with this volunteer was just very much different.

And then when we scanned him

and didn't find any brown fat,

I didn't even think about it.

So when we scanned him, we didn't see anything.

I told the PET CT people who like,

oh, you put up the wrong scanning.

Blame the technology.

Yeah, the technology was like,

this scanning looked like the thermonutrile day,

the thermocomfortable day

where we also scanned them to see

if they have any brown fat.

So you have made a mistake, I was pretty sure.

And they re-analyzed this scanning

and they just concluded, well, the scanning was fine.

The experiment went well.

It was just that he didn't have any brown fat.

So he was like what we just in the paper called

the brown fat negative.

So he didn't have any.

And in my studies, it would be called a knockout.

So it didn't have any brown fat.

So the observation with him,

and I think that's interesting,

is that he both shivered very early on

and didn't regulate his temperature as well.

He also told me that then he was like a five

on the scale of how comfortable he felt with the code.

Out of.

So it was from one to 10

and five being thermocomfortable

and 10 being very cold and one very hot.

So on this like scale up and down.

And he was like more up and down on this scale

than any of the others.

It was an observation that I did.

But we did see in his blood samples also

that his blood samples looked a bit more

like the control group.

Also his insulin levels

were like the control groups

or a little bit higher than the other winter swimmers.

And he also had his blood glucose clearance

was not as fast as the other winter swimmers.

So he was like an outlier, what we call it.

And in the analysis,

we also had to take him out of the analysis

because he was an outlier.

So the results showing that the brown fat

is more efficiently activated in the winter swimmers

is without him having him in that group.

But it didn't ruin the study.

If I tried to put him in as well

and it didn't ruin the results or anything

but just to keep it more clear,

we put, we took him out of the analysis.

Yeah, so he was a mutant knocking.

Yeah, and I'm sure they're out there.

Very interesting.

So if you shiver early then perhaps

you have less brown fat to begin with,

although it's hard to conclude from one person,

that's sort of the implication there.

Or you haven't adapted to the code.

So you should build that up, yeah.

So in addition to looking at regulation of blood sugar,

brown fat, metabolism and so on,

were there any markers that you examined

in the deliberate cold exposure group

as compared to controls that revealed to you

that deliberate cold exposure

could have additional benefits,

say for immune system function

or for any function for that matter.

Yeah, so for, we looked at inflammation,

of course we measure outcome of blood pressure and so on,

but we also measured IL-6 in the study

just to see also an inflammatory and inflammatory marker.

So IL-6 went up and it also follows with IL-10.

So that is also very known in the literature.

So we measured that and I think it's very important

to think about the cold exposure and the heat exposure

as something that then lowers the inflammation in the body.

And if we can do that,

we will have an open door for preventing lifestyle diseases.

So for type two diabetes,

but actually also for some mental diseases as well.

So as known as depression and anxiety

and also Alzheimer's disease,

which are all associated in research,

also newer research showing that inflammation

increases the risk of depression and anxiety

and Alzheimer's disease with neurological diseases.

So if we can decrease inflammation in the body,

we will decrease our modern lifestyle diseases

but also these increasing mental diseases

that we see in these modern lifestyle times.

So I think it's very interesting

that we can go out in nature

and we can use these natural stressors

and I don't want to have it sound very romantic or anything.

It's just exposure to temperature actually,

just a cold or to heat

that is gonna twerk our body into a natural state again

and reset it where the homeostasis,

the balance is lost a bit.

So the body is gonna repair itself in that way

and I think it's beautiful that we can do that

just by changing the temperature of our body.

And although people are very scared of doing this

because in our times,

we have been away from cold, away from heat,

temperature for decades now

since we isolated our houses better

and we are more sedentary, we also sit more indoor,

we don't move as much.

So this very modern sedentary lifestyle

has made us more temperature comfortable, just neutral.

So no wonder, I mean, that obesity is increasing.

We don't expose ourselves to the natural stresses

that we did earlier on in our involvement

but also up until maybe the 70s, the 60s

where we started having more comfortable lifestyles, right?

And obesity increases in the 80s.

We can see that from statistics.

So I think that if we can take in cold and heat

and you mentioned other things also before

but of course exercise is very important here

and also a bit of fasting actually

because it all increases the hermetic stress in the body.

So it doesn't have to be other than natural stresses

to the body which then could keep us

in that natural balance again.

Could we talk about what I refer to as the Soberg principle

which is to end on cold?

And the reason I called it the Soberg principle

is because in reviewing, oh, by the way,

I wasn't a official reviewer of your paper

but I mean in reading and reviewing your paper

for its after published contents,

I noticed that you had people end on cold

and this has been a long standing debate

in the deliberate cold exposure community.

Should you warm up with a warm shower afterwards

or get back in the sauna?

What should you end on cold or end on heat?

And the Soberg principle says end on cold

as I understand it,

in order to force your body to heat itself back up

and thereby increase metabolism further still.

Is that right?

Yes, so when you end on the cold,

you force your body to heat up by itself

and that will require that you activate,

you keep your brown fat activated

and also your muscles which is a good thing.

It's a good collaboration to keep your thermogenesis up

and that's like an exercise

even when you go home.

So in that way,

you don't have to think about your cold exposure

or dipping in your plunge or open sea or what it is

as just an exercise that you do for one to two minutes

and then it's over.

If you end on the cold,

you have an exercise for your body going on

for hours afterwards

and that's not only on your metabolism

but it's also gonna keep your neurotransmitters

activated as well and increase that

because your body is still cold.

So you need those neurotransmitters

to activate the brown fat as well.

So that's gonna make your brown fats

that's more efficient

and also your muscle cells more efficient

so increasing mitochondria in the cells

which will then generate heat very fast.

So if you have done this for a few times,

so maybe three, four, five times being new to this

but have tried it a few times,

you will notice a switch where you like feel

that you get easily warmer

and you can keep yourself warmer.

And that is also what was shown in my study

is that the winter swimmers were physically warmer

on the skin compared to the control group.

So they-

When they are out of the cold.

When they're out of the cold, just relaxing

and we tested this in on the days

where they were sleeping in the lab.

So we could see that they had a more activation

of the brown fat, a higher temperature.

So probably because they also lose heat,

they have a higher heat loss to the body

compared to the control group

because they have a more vascular skin

because of the contrast of cold and heat.

So they lose heat faster from the body during that day

but is that a bad thing?

No, probably not

because that's gonna keep your brown fat

and your muscles a little bit activated.

So you will have to, it has to work to keep you warm.

And I would hypothesize that it also might lead

to some of the subjectively reported improvements in sleep

because in order to fall asleep,

you need your core body temperature

to drop by about one to three degrees.

So it's not just sufficient to be sleeping

in a cold room and under the blanket,

you also need your body temperature to drop.

And so what you're saying, if I understand correctly

is that by forcing, by ending on cold

and forcing oneself to heat up naturally,

that increases the brown fat stores,

which I sort of see as kind of like the oil in the candle

of the furnace, that is thermogenesis,

and that in turn leads to increased heat loss,

which people might think,

oh, I don't wanna lose heat from the body,

but there are times when we want to lose heat from the body.

Basically, it sounds like what we want

is to be a very efficient heating and cooling system.

That it's not about being cold or being hot,

it's really about keeping the system tuned well,

keeping the oil in the candle, this brown fat functioning.

Yeah.

Could I ask one question about fed or fasted?

Is there any, or rather, are there any known benefits

of doing deliberate cold exposure and or sauna fasted

versus after a meal, say within the last hour

or something of that sort?

I do my deliberate cold exposure first thing in the morning.

So in general, I'm fasted

because I don't eat until a little bit later in the day.

But what's known about that?

And was that looked at in your study?

I know you measured glucose,

but that was as a separate test away from the cold.

Away from the cold, yeah,

but I also tested glucose on the days, on the cold.

So we measured that as well on the cooling days.

Specifically on fasting and fed, I don't know.

I don't think that I have seen studies specifically on this.

Okay.

More science needed.

A number of people asked about the use

of deliberate cold exposure

to offset some of the symptoms of various diseases.

Now here we're not talking about curing disease,

we're talking about offsetting symptoms.

One question I've seen quite often

is whether or not people with Ray Nodes syndrome,

this is a syndrome,

and my high school girlfriend had this syndrome

and I'll never forget,

we went, we were at a school dance together.

And this was when we first started dating

and she had Ray Nodes,

which leads to very poor blood flow to the extremities.

And she was very cold,

so she left to go to the bathroom

and warm up her hands in the warm water.

And I was left standing there at the dance

and people came up to me and asked,

why I was there and who I was there with.

And I kept telling them who I was with

and they didn't believe me

because they couldn't believe that she would be with me.

Made total sense if you knew me at the time.

I was way out of my league with her at the time.

I like to think eventually I caught up,

but in any case,

she was in the bathroom for about an hour.

So at one point I did consider the possibility

that she had just left,

but indeed she hadn't,

she warmed her hands back up,

but people with Ray Nodes suffer from this thing

of very, very cold extremities.

Their fingertips will even turn blue

as if they were starting to get frostbitten.

It's quite dramatic.

And that question gets asked,

whether or not there's any use of cold

to try and increase the elasticity,

the plasticity of the small capillaries and vessels.

By everything you've described up until now,

it seems like that would be a logical thing to do.

And in addition to that,

whether or not people with autoimmune conditions,

people with any other types of conditions

are known to benefit from deliberate cold exposure.

I'm not aware of any studies,

but I get asked about this a lot

and there were a lot of questions about this for you

in the Twitter feed.

Yeah, thank you for those questions

and I get them as well on social media.

And I have to say that I haven't seen any studies directed

on this outcome and measuring Ray Nodes syndrome.

I do know that it's not that rare actually a problem

and I know that many women or more women than men

suffer from this,

but logically it would help them

if they exposed their hands to cold

and also heat to make it more vascular.

But, and I have heard from people saying that it had helped them

but also heard for some others saying it didn't help them.

So studies are needed on this specific topic, I think.

I hurt my hands when I go into the cold

and I don't have this syndrome at all,

but I keep my hands above the water.

You do?

Yeah.

I do that, often I take a little bit of a swim

and then of course I have to have my hands in the water,

but it helps me when I then get back to the daddy

and then take my hands off

because then I can stand there for a little bit

and get my one to two minutes exposure

and then I can go off because then otherwise

that would stop me from being in the water enough time

that I, as long as I would like to.

So people suffer from having this pain in the fingers

and it can be very intense.

So just take the hands up a bit from the water

and that's gonna help you.

Also boots, neoprene boots, it's gonna help on the feet.

Some people have the hurt, feel the pain in the feet

and on the ankles and that's gonna help them also a little bit.

Okay, so there is no problem with keeping hands out

or feet in neoprene booties

if people feel the need to do that.

If pain of the hands or feet is a barrier

for people doing deliberate cold exposure,

then it seems it would be okay to do,

to keep hands out or to keep your feet in the booties.

Yes, because then you do get the exposure,

but of course hands and feet are very potent places

in your body to get a fast activation

of your nervous system, of course.

But if you can just, you can also just dip them

and then take them up.

It's still gonna activate that,

but you have your full body is covered in co-perceptors.

You'll have a full activation anyways, so yeah.

You are providing very reassuring information to people

because I know a number of people

that do not like to put their hands in.

I find that the more of my body I get in,

the more comfortable I am,

I don't know if it's psychologically and or physiologically.

I find that if where there's an interface

between the water and the cold, it's most uncomfortable.

So I prefer to just get everything under.

I keep my head out.

Although these days I've been dunking all the way in

and then coming out and then dunking once more

with my head under before I get out after the plunge.

That raises a different question.

Now we're getting into kind of the practicalities

of deliberate cold exposure, which I think are important.

Sometimes I'll experience, and I hear from a lot of people

that they'll get a kind of back of the head headache

at the interface of the water,

when they're doing cold immersion to the neck.

I assume this has to do with blood flow,

that there's vasoconstriction right up until the neck

and in the region surrounding it,

but that maybe there's still blood flow to the head.

But do we know what the origin of these headaches is?

And again, this doesn't happen for everybody,

but some people do experience them.

Okay, yeah.

I haven't really heard about that one specifically.

So, but I would say that there are different reasons

for maybe keeping your head out of the water.

But it seems like maybe for some,

that could be a reason for like,

just getting like a quick head dunk.

Going all the way in.

That's what I've started doing to eliminate.

I wasn't getting headaches, but I could,

I noticed that interface and I wasn't in the rest

of the experience of it so much.

So I started dunking all the way in.

I noticed in some of the photos that you've put out

and in your book that you'll sometimes wear a cap

while you go in.

And well, it comes from different reasons.

So let's talk about some of the physiological reasons.

So when you submerge in cold water up to the neck,

studies have shown, and this is from Denmark,

studies from Bispepia Hospital,

that when you submerge into cold water up to the neck

at zero degrees, so zero degrees Celsius, very cold,

you will have a decreased blood flow to the brain

by around 30 to 40%.

And makes sense because you activate

the sympathetic nervous system.

And therefore you will have a less blood flow

to the brain, makes you maybe a little bit dizzyer.

Proof again that you need a heart more than a brain

because when the sympathetic nervous system gets activated,

blood flow is maintained to the heart to keep you alive,

but obviously taken away from the brain

to keep you from thinking.

That's why it's hard to think when you're stressed.

Yeah, well, the muscles and your vital organs need to,

you have to be able to run away from that tiger, right?

The rationale makes total sense.

And who am I to disagree with mother nature?

Well, but yeah, so one of the reasons being

that you should keep your head out of the water

is that you could increase that decrease

in blood flow to the brain further if you dunk the head.

So there's just a very nice paper from a research group

in Canada where they have collectively looked

at different papers where they compared heat loss

in the papers where they dunked the head

and compared to heat loss,

submerging up to the neck to see how much extra heat

do we lose from our core when we dunk the head.

So, and I think it's very interesting

that if you submerge up to the neck,

you have a heat loss of 11% from the body core.

And when you then also dunk the head,

you will increase that heat loss rate by 36%.

So that means, I'm not saying that I'm not here to say

what is right and what is wrong.

I just think that people should know the information

so they can for themselves evaluate what is best for them.

But if you increase your heat loss rate by 36% from your core,

that's gonna increase your afterdrop,

which we touched upon a little bit earlier, even further.

So that's meaning that you are closer to hypothermia

than you are if you just submerge up to the neck.

So you should really think about

whether this is like something that you want to do

or if it's just better for you

not to get that cold in your core.

The beanie is also because I have a little bit

of sensitive ears.

So it meaning that if there's wind

and because we swim in the open sea in Denmark,

we have a lot of wind.

Our wind, our conditions are just very rainy, very windy.

And when the temperature is also freezing,

you could get this, what is that called?

So very cold and lightheaded just from wind.

So if you also submerge into cold water

and you then get up,

you will get a brain freeze immediately.

So it is enough to just go up to the neck

where a beanie should just not get dizzy also

because the heat loss is increased, of course,

but also the blood flow to the brain has decreased.

So the beanie will keep you a little bit warmer

so you can stay for one to two minutes.

So it's just a way of like getting around

some of the conditions also.

So people can choose that if they feel that,

but it's quite normal to do in Scandinavia where a beanie.

I love it.

And so for those of you afraid of doing

a two minute cold shower,

what Dr. Silver just described,

let's you see how she and others are capable

of doing things far harder than that.

When the way you describe it with the cold wind

in Scandinavia and is quite striking.

Along the lines of covering the head,

there's this seemingly paradoxical thing

of people going into hot saunas and wearing wool caps.

If you go to a Banya or you go to a sauna

and there are people who are, well, from Eastern Europe

or typically are Finland or Russia or Ukraine

or elsewhere, what you'll see is that many of them

are wearing wool caps in the sauna,

which many people think is to make it hotter.

That's actually not the case.

It actually insulates you from the heat environment.

The sense of urgency to get out of the hot sauna

is a brain driven mechanism.

And so the reason that people wear wool hats in the sauna

is it actually lets you stay in the sauna longer

because it takes a lot of heat to the skin

before you feel that you have to get out.

Whereas so when you insulate the brain,

you don't get that signal.

It's pretty interesting.

I've tried this before just by putting a towel over my head

in the sauna and you can stay in there much more easily

and for much longer.

As we talk about these different stimuli

for the hermetic response, the adaptation distress,

it occurs to me that the big ones

in our evolutionary history have been light, right?

I mean, you were talking about seasonal changes.

We know there, especially as you go up to Nordic countries,

there are seasonal changes in the amount of light

by time of year, dramatic ones in fact,

less so at the equator, of course.

Light, temperature, food, movement.

And it's sort of interesting and at the same time,

perhaps it should have been obvious to us

that there are stimuli that our bodies have evolved

to adapt to in very powerful ways.

And so the idea that temperature, heat and cold

could evoke these tremendous physiological changes

that are beneficial for us,

probably shouldn't surprise us at all.

I mean, this is why, I mean, these are not esoteric mechanisms.

They're actually the foundational mechanisms

by which our bodies and the bodies of other animals adapt.

So I do have a question about the different ways

that people could approach deliberate cold exposure.

So for instance, children.

I've been to Bonyas where there are kids,

six or seven years old with their parents at the Bonyas.

And so they're in hot sauna.

I'm not suggesting people do this

if they're not adapted to it.

And talk to your parents' kids

and talk to your kids' parents, talk to your doctors.

But it is remarkable.

I mean, children doing sauna from a young age

or deliberate cold exposure, are there any date on this?

And is it safe, assuming that obviously they can swim

and they're doing this in a tub or shower?

And then I'd also like to ask you

about are there any additional male-female differences?

I know your study focused on men,

but other studies have focused on both.

And you, of course, are a woman

and can attest to your own experience with this.

So children, men, women, difference is there

in terms of protocols.

Is there anything that people should build

into the structure of their deliberate cold exposure

that's unique to that?

So yeah, so this was an uncold exposure.

So yeah, I think that starting with the question

about children, I think that it's important to think

about as children are smaller than adults.

So we cannot really completely transfer all the information

and the benefits and also protocols for how long

and stuff like that to children.

We cannot do that because they are just smaller in mass.

And one study that actually improves this is a study

where they have compared heat loss in children, boys,

who were 12 years old, compared to adults, men,

and looked at the heat loss of the core temperature

and exposed them to a one or two minutes

cold exposure, so immersion up to the neck.

And what they saw was that the boys in this study

could actually defend the core temperature

in the same way as the adults could,

but they had to use their muscles way faster.

So it means that they couldn't stay for as long

and they use more energy to defend their core temperature

compared to the adults.

But for one minute, it seems that they could actually,

but they will be colder when they then come out

because they are smaller in the mass to their ratio, right?

So it means that if the surface is so large on children

and their mass and muscles being smaller to that ratio,

it means that they can be in the water less time

before they get hypothermic.

So just think about that, they are just smaller.

They can't defend their temperature for a very long time.

But in this study, they saw that for up to,

I think it was a minute or so,

they could one minute, yeah.

I'm glad you mentioned hypothermia

and smaller-bodied people, children.

I used to do some Pacific ocean swims in the morning

without wetsuits and I adapted to it pretty quickly

and these are fairly long swims

and we brought an excellent swimmer with us

that was interning with me for a while,

is 16 years old at the time and very lean.

And he wasn't small for his age,

but he was smaller than us.

And it was all guys on the swim that day.

Sometimes women join us and he got hypothermic

and he's an excellent swimmer

and he didn't report feeling overly cold,

but fortunately we got him to shore and he did him up again.

So he lived, I don't think his mother's gonna ever

let him go swimming with us again.

He's thriving in the world.

He's a university student now and he recalls that swim.

I mean, this is why you always want to ocean swim

with a buddy, with people.

Yeah, he became hypothermic.

His teeth turned yellow, he was got slurring his words,

he wasn't making sense, we got him on the shore

and he was kind of drooling and a little semi-euphoric

and then kind of, hypothermia is no joke.

So I think, yeah, so I'm really glad that this is coming up

because the cold is a powerful stimulus

and kids are at a, and smaller-bodied people

are at a greater risk of hypothermia.

So a good reason to approach it with caution,

maybe start with cold showers,

get then cold immersion and still water.

Natural water and open bodies of water,

of course, are always going to be more dangerous

for other reasons, currents and things of that sort.

Yeah, exactly, I'm drowning.

So an important note there,

what about any additional male-female differences

or similarities that we should be aware of?

And this comes up all the time on social media.

Anytime I post anything about a study,

it's what about women,

because oftentimes there are differences.

Yeah, yeah, and we also just talked about

the difference in temperature in men and women.

So it means that if we did,

if we replicated my study in women,

it could be that they would have enough,

you can say cold exposure with just nine minutes per week.

It could be because they apparently are also just colder

and they have increased metabolism in their brown fat.

It's just they have more brown fat.

It could be, but this is just something

that I frankly don't know,

but women also do cold exposure winter swimming

with the 11 minutes protocol.

I do it myself and feel good about it.

So I would say that women also regarding activation

of the brown fat, it should be the same in theory,

but I don't know if women actually do need

to have another protocol

when it comes to this rapid cold exposure.

I think that it's another question

if we are talking about ice swimming,

when it comes to how far can you be in the cold water

without getting hypothermic,

then there will be differences in men and female,

but if you do this cold exposure

for a very brief amount of time,

which is what I try to talk about,

what we call also micro-stressing the body

to increase the hermetic stress, the healthy stress,

then this is such a short amount of exposure

that it's fairly the same.

I think women can look at this

as a fairly good protocol for them as well.

I always say that if you really dread the cold

and don't like the cold,

then you are a perfect candidate

for using deliberate cold exposure

because the sympathetic,

aka the stress response will be greater

and thereby the adaptation to that shorter

one or two minutes is going to be much greater.

For people that are perfectly comfortable in the cold,

it's harder to get an adaptation response

the same way that if somebody is very strong

and they can lift a very heavy weight

that that very heavy weight is unlikely

to evoke the same degree of adaptive responses

if somebody is not quite as strong.

So another reason to keep these exposures

relatively short and more frequent

than to do longer duration exposures frequently

however, let's say somebody only had two days a week

to do deliberate cold exposure.

Maybe they don't have access to a sauna, maybe they do.

Would you suggest that they get in for one or two minutes,

then get out, then get back in for another couple of minutes,

then get out and call that for four or five minutes

to try and get to that 11 minutes total per week

as opposed to getting in for a full five minutes

and then getting out and coming back a second time that week.

I know this is getting down into the weeds

but these are the sorts of things

that I think people really want to know

because a lot of people either don't live close

to a body of water or don't have a cold plunge

that they can do this with

although cold shower apparently works too.

So most people live close to a shower.

Yeah, so definitely I think the changes in temperature

is what is strengthening your cells in the body.

So if you can do the short amount of exposure

and then get out and get back in, that is gonna,

you can say strengthen your cells

because you are challenging them

to adapt to changing temperatures.

So during one session, you can change this, right?

You can do it if you are able to go to cold water

but also a sauna, then you just do it that automatically

you will have a change in temperature

but you could also do it with

variating the temperature in your cold plunge

if you have a plunge or if you have an open sea

or you have seasons even, we have that in Denmark

so we have four seasons

and the temperature is gonna vary with that.

So we have nature who can just change this for us

and we don't have to think about it.

But if you have a cold plunge, well,

then I would say that changing the temperature

is what is gonna create this hermetic stress

and also keep your cells on its toes, you can say

because the body will still be stressed

to try to adapt to the new temperature

as it's seen as something actually toxic to the body, right?

It's a small piece of toxicity

that you are exposing yourself to.

You don't have to swallow it

but it's enough that you touch it actually.

Yeah, great way to frame it.

That brings me back to this idea of circadian time

in your study you didn't control first.

The specific time of day

and now I'm realizing that may be a great asset

to the whole thing.

So we know for instance that our bodies go through

pretty dramatic shifts in temperature

from the time we wake up.

Our body starts heating up as we wake up

and continues to heat until the afternoon

and then starts to drop in the later afternoon

and then assuming all things are working correctly

that body temperature drops and we sleep.

So I could imagine that doing deliberate cold exposure

at different times just by way of convenience

or by way of intention could be very beneficial

because my body temperature is going to be quite a bit warmer

at one time of day versus another

and in that way keeping the system tuned.

And that's really what I keep hearing coming through

as you explain these data

and all these beautiful studies, yours and others

is that it's not really about getting cold.

It's about going from warm to cold and from cold to warm.

It's not, and I love this idea

because I probably said this a hundred times

on my podcast and a million times in my life

and I'll continue to,

which is that biology is not an event, it's a process.

Like these metabolic and thermoregulatory processes

are indeed like the turning of a knob.

It's a verb, as opposed to a noun.

And so I think if people can internalize that idea

that they're going to have a lot more flexibility,

a lot more fun and get a lot more benefit

as opposed to thinking, okay,

I need to get into X degrees of water

for X amount of time on X number of days

in a very rigid way.

And I get this question all the time, how much and how cold.

And I mean, it's just like, well,

because we also don't have studies showing exactly

if you just keep five degrees in your water

and you do that for a month, then what happens?

Maybe in the future we will know much more about this

and I'm sure it's gonna come and I really hope so.

But I just think by logically changing that temperature

up and down, up and down,

and you also do that in your water,

it doesn't really, it's not that important

what temperature you will have your water then,

then just keep changing it, going up and down.

It could be all up to 12 degrees Celsius.

You're gonna activate your brown fat anyway.

So I mean, 12, 19 degrees cold air

is enough to activate your brown fats.

So maybe we don't have to go as cold

as I think many people think.

And putting ice even all the time, you don't have to.

I don't think it's necessary to expose yourself

to that cold temperature all the time, but vary it a bit.

So keep the system off balance

and it's the way to keep it tuned.

You mentioned a study that is more recent

or an ongoing that's not published.

If you're willing, could you share maybe some of the data

from that findings from that study

with of course the cue to everybody

that these are not yet published data.

So the conclusions could change,

the data could change for that matter.

Yeah, so we haven't analyzed all the data yet.

And I know from the study that we did publish

that we would need to look more of the data.

So I don't really have any results yet that I can share

because we are still in very preliminary analysis of this.

So I wouldn't know yet what to exactly say about it.

But what we looked at was both men and women method.

So that's coming.

Oh, that's fantastic.

That answer is going to please a great number of people

and intrigue everybody.

So, well, I want to really thank you

for coming here today to talk about your work

and the incredible direction that it points to.

Because I think that, you know,

no one study is definitive,

but your study really again stands as a landmark

in the landscape of exploring deliberate cold exposure

and heat, how it can impact

and potentially impact our health.

Because frankly, there just haven't been

that many high resolution detailed modern studies of this.

There have been studies of sauna.

There have been some studies of cold.

There are a lot of groups in physiology

that work on hypothermia and very cold exposure.

But most of the temperatures used in those days

just aren't practical.

So first of all, I just want to thank you

for doing the work that you've done

and for the work that you continue to do.

I'm waiting with bated breath, as they say,

to hear the results of this study

that's ongoing on both men and women.

So we'll have to have you back to inform us about that soon.

And I want to thank you for the incredible

public education efforts that you've been doing

on social media and with respect to your book.

And we, of course, will put links

to all of those things in the show note caption

so people can learn from you

and can continue to learn from you.

We certainly need more scientists

who are both experienced with doing hardcore research,

as it's called, and who also do the practices.

I think that's a wonderful additional asset.

You're not just behind a lab coat

or bundled up in a down feather jacket

as everyone else is getting into the cold.

You do these things and that you are so open and generous

in the way that you share knowledge,

which includes coming here today

to share knowledge with me and our audience.

So thank you ever so much.

You're very welcome.

I am so pleased to be here

and thank you so much for inviting me.

And I could explain my study

and I can share some of my insights from doing that.

So I'm very grateful for being here.

Delighted and we'll have to have you back again.

Thank you for joining me for today's discussion

all about deliberate cold

and deliberate heat exposure science and protocols

with Dr. Susanna Soberg.

If you'd like to learn more about Dr. Soberg's research

or you would like to learn about the research

of her institute, the Soberg Institute,

please see the links in the show note caption.

Also in the show note caption,

you can find a link to Dr. Soberg's excellent book,

Winter Swimming.

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