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

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 sober'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 impact of heat on

various aspects of human health as well

as specifics relating to sauna versus

Ice versus cold swimming showers Etc

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

and 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

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first box I'm pleased to announce that I

will be hosting two live events in

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12th the second live event will take

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Live Events will include a lecture and a

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no overlap with content covered

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please go to hubermanlab.com tour and

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access to tickets once again that's

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huberman to access tickets 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 back story of how we got connected

which was that for many years I've been

interested in cold thermogenesis it was

the topic of my seniors 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've been

interested in this area

but there's been a real uh 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 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 reached 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

going to 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 yeah and for those that

haven't done it might start to peel back

some of the 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 going to activate

your

um your sympathetic nervous system so

get all these neurotransmitter going in

your body and so your your

catecholamines

um let's just address that we are taking

a cold plunge for example so if you are

very hot for example

um before you go into the cold water

it's going to feel less it's going to

feel less stressful but the the

temperature difference from your skin to

the cold is definitely it's going to

give you a shock but your core

temperature is warmer and that's going

to feel a little bit better so that's

why when people go into a sauna for

example and go out in into the cold

water they they they can do it easily

easier them if they were called

beforehand could I just um ask you a few

questions so you you mentioned the

sympathetic nervous system which for um

people listening who aren't familiar

with that is that the branch of our

nervous system that's responsible for

creating accelerations and heart rate

um 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

so it's not always about stress and then

you mentioned the catecholamines which

um 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

um 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 uh what

kind of Protocols are the are the best

way or also for which outcomes of course

so if the temperature is very cold and

you feel that 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 code shark so the code stock is

activation of your sympathetic nervous

system and these activation of the the

catecholamines which you just mentioned

before does the shock mean that I'm

having trouble controlling my breathing

is that a good gauge uh yeah you can say

so because that's kind of like how we

Define it so you hyperventilate so you

have a faster

um breathing rate

um so that increases also because you

activate your gasping reflex if you are

new to this

um but if you are adapted it it kind of

subsides with time with the 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 hypertension ventilating response

every time you go out in the cold water

so this is like building up your

resilience building building up your

adaptation is gonna make this short like

subside a bit so it's 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 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

um if running hard you know running fast

and breathing hard is uncomfortable you

can slow down or walk if um you know

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 um 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

um and these are very tough individuals

they're used to going without sleep and

doing hard high consequence higher 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 you know

like they looked stoic anyway to me

um there were a few whimpers no cries

about a third

um

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 someone

actually didn't actually go in

completely

um 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 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

uh dread the code even more and you can

say the more people are pushing the cold

away they might feel the co-pain even

more so they they they would definitely

people who are maybe the soldiers you

just talked about they some of them

might be already adapted to the gold

cold so if they are not scared of the

cold they go out and they embrace the

COPE 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

also have the co-pain more um feel the

co-pay more if they're if if you avoid

it so the more you avoid the cold the

the more pain 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 um 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

it comes because they're they are very

different exposures of the cold to your

co-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 there are of course covered

totally and then and the molecules are

closer to your skin you have a more

potent

um activation of all your code receptors

in the skin so that one will definitely

activate your other enormous nervous

system more and Rapid compared to going

out in a t-shirt in the cold wind just

go for a walk

um but that is also something that's

going to activate your sympathetic

nervous system meaning then that you

have an increase in norepinephrine and

you will activate something called the

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

um because it's so much to talk about

there uh what about cold shower I mean

obviously cold showers somewhere in

between yeah

um being out outside in the Air Cold Air

versus uh being immersed up to the neck

it if we had more studies on on cold

showers we would learn more about how

does that activate our metabolism how

does that increase our neurotransmitters

in the brain which could also have an

impact our on our mental balance so I

think that would be interesting for the

future

um but what we do know is from from 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 in

the body to keep our

um 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

like always like temperature regulating

our body and then we have uh the the

muscles which will secondarily start to

shiver and that's going to increase our

um temperature in the body but as soon

as you go into a cold shower you

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 this

actually activate the brown fat so if

someone out there wants to do a study I

think 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 going to stand under the shower with

it hitting their head some people the

back of the neck you could direct people

to do it yeah but it's a little bit um

more difficult also I think uh for you

and I are both research scientists

there's a little bit of a um

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 and

for most people coming to a laboratory

in the first place let alone being

observed while they shower whereas when

you get into cold immersion cold

immersion you're getting under the water

and you know some people might roll

their eyes and say okay really is that

the barrier but you know 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 um the process of

getting people to the laboratory and

having them Park and find the lab and

you know it's a whole new environment

government with people in lab coats and

people moving around and Where's the

restroom I mean there's there's a

certain amount of stress just associated

with taking part in a study for most

human subjects so

um I uh totally agree however we need

more studies of cold showers it's just a

harder environment to control in my 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 oh

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 this seems that

I I think that of course in the future

we will know much more about these

Pathways but what we do know is that the

co-receptors will send a signal to our

temperature regulating Center in in the

brain so hypothalamus

um and that's gonna be

um taking in this message and we have so

many Coke receptors in the skin so it's

going to be very fast as you can say if

you immerse the body into cold water

this is going to be so rapid so it will

have a rapid increase in

neurotransmitters in the brain so no

adrenaline adrenaline and cortisol and

which is not that much but it's but it's

still there so you have this increase in

no adrenaline which will then

immediately activate the the brown fat

because the you can say the activator is

the most potent one cold and no

adrenaline and that's going to activate

the brow fat but there's also a direct

pathway from the cold receptors in the

skin to the to the brown fat which

really shows that if because of these

different Pathways it shows that that it

could be that this tissue to keep us

warm was was

developed in in our evolvement as humans

to keep us warm and to save us whenever

the temperature now on our skin berries

just a little bit to keep us in that

right homeostatic balance so we don't

get hypothermic

um 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 um maybe a

temperature regulator in our 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 at

um even though the muscles are starting

to shiver so there's an extra pathway

that way to keep our our temperature up

so muscles and brown fat are working

together to to keep us warm so we don't

suffer too much in the in the cold water

it's super interesting and what I here

are 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

um as you uh said so so eloquently the

when something is very important to our

survival or and or evolution

the brain and body uh install multiple

mechanisms for it not just one and um

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

um I want to talk about Brown fat in

depth and learn from you more about

Brown fat

um before that however I want to ask

about shiver

um I've heard that shiver

causes the release of succinate

um which then activates the brown fat is

it known whether or not inducing shiver

is important and when should P 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 coal plunger a cold

shower then getting out or 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 it was shivering is good because

that increases your metabolism and

that's going to 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 hypothermic

so if you don't if you don't sit in the

cold water for too long

um 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

um your body because it as soon as you

get into the cold water all the your

blood vessels is gonna constrict because

you need to keep your blood in your core

and and keep your vital organ swarm so

as soon as you get up that those blood

vessels will open again and the warm

blood will flow out and get colder and

then flow back again into the core and

that's going to 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

go 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 um 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 right and then am

I right in thinking that then the shiver

activates Brown fat which then warms me

up again yes that's why you should end

on the cold but we can get back to that

yeah let's talk about yes ending on cold

is um you know it's what I refer to as

and what has now become known as the

soberg principle which is um a really

important principle about the importance

of ending on cold

um and not doing what I do which is to

get into a hot shower or back in the

sunroom we'll get back to that in a few

minutes so

um that's wonderful

um 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 to you know the

chattering of the teeth and um and it

feels like a loss of bodily control

which really it is it's it's an

autonomic response yeah but I don't

think that people should should avoid it

that much it's just like seeing

shivering as a way of your body in in a

like it's training it's training for

your for all yourselves it's training

for your muscles it's training up your

metabolism and that's going to 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 and

your body it's going to create what is

healthy stress it's called homiesis in

the cells and the more you expose your

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

activate trading and also um at keeping

you healthy so as long as the cells get

exposed to this it's going to keep them

on its toes you can say because it

becomes more robust and increasing these

heat shock proteins and kosher 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 is going to do to your

muscle cells and and but the same kind

of like training is also what you do

when you go out and and into the cold

water and submerge into cold water

because that is just your code training

center you can say that and 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 uh

actually to reach for and try and

experience the same way that with

exercise

um 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 and

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 um 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 uh I think it was European

Journal physiology it was uh the

European Journal 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 no

you're asking for the 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 you know in your study you

should 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 um exercise on an

exercise bike or go for a hard run but

then if I go hiking uh 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 of the exercise what are what are

some of the fitness adaptations of

deliberate cold exposure

yeah so what happens is that you 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 you feel

more comfortable in the code so you're

gonna you're gonna build your adaptation

which happens on a metabolic level which

is going to be the brown fat so you'll

have more activation of your brown fat

the mitochondria in the the brown fat

cells are going to be

um you have more of those and they will

be more efficient at heating you up

because it expects the body expects you

to to do this again so you are prepared

in a way the capillaries in your skin is

also it 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 be become

better at going into the cold water in

that way so the body makes this

mechanism and changes your body in a way

so you can expose yourself to the next

time right and and also you will have um

also um your um stress response will

also be subside a bit so you have a less

increase of your catecholamines

um with time

with time also you have because of this

activation of your brown fat or your

muscles you have an increase in them in

in your metabolism which will then make

your insulin sensitivity better and this

is shown in in studies for example um

there's this interesting study I found

just before I I started my PhD which was

from um keeper stoma

um at L from 2016 where they measured um

metabolism

and not in 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 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 so 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 selling how much

inflammation you have in the body and

because it didn't measure Brown fat I

figured that it could be that was the

missing link that was the one of the

explanations to why we see this um less

inflammation in the body

so um the longer outcomes the long-term

outcomes could be that you lower your

blood pressure and have a lower heart

rate and you also

um have a better insulin sensitivity and

better glucose balance but that was

shown it that is shown in my study I'd

like to take a quick break and

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we'll get back to the insulin

sensitivity and glucose balance that's a

in an impressive list of benefits

um you know 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 oh you know blood

pressure it's not you know people want

to hear about the inflammatorium and the

microbiome and all of that stuff is

really interesting but

um I think that blood pressure doesn't

get enough

attention

and we have spoken to on this podcast to

Dr Peter attia who um is an expert in

longevity and health span and things of

that sort and 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

uh not to get 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 it's

interesting because we don't think about

blood pressure that much anymore

um as a as the kind of people interested

in health optimization and health 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 yeah um

let's talk about Brown fat and um if you

if you're willing I'd love to drill into

Brown fat at a deep level

um again my understanding of this is 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

uh maybe more widespread than when I

learned in school I thought it was I was

taught 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 um 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 the organs but please educate

me um tell me where I'm wrong and expand

my knowledge on Brown fat

okay yeah you're not wrong but um it's

definitely it's true that there are more

locations of the brown fat than we

previously thought

um there's this very nice study from

2017 by Leitner L where they had made

these opacities uh overlays of um their

subjects but you can see where in the

body do we have brown fat and where can

we grow more Brown fat

um so to say um so the brown fat is is

very plastic so it means that it can it

can grow and they can decrease and this

is proven in in studies where we have

seen um

um people with a fair cryocytoma it's

like a very specific cancer type where

people where from the 70s where we can

see that if they have this specific kind

of a cancer type

um they have a they have this tumor on

the adrenal gland so they have like a

huge increase in NOAA adrenaline and

because of that you don't have this

continuous activation of the brown fat

and they have grown a lot of brown fat

in the whole body or abdominal where

it's located in these six different

places but it is just like very much

compared to like normal people

um and what they then see what we

learned from this study is that brown

fat can apparently grow if you have an

increase in no adrenaline 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 it

activates also your sympathetic nervous

system so they have also showed they

have high blood pressure they had

they lost a lot of weight of course

because this is activating your

metabolism so they they found luckily

that when they removed this benign a

tumor uh that uh the brown fat

um 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 in its way

of like it can grow and it can decrease

again so that's very good good studies

to to see what what the body is capable

of but we don't of course want all that

brown fat we just want it to be um 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

and people

um Studies have shown that there is an

association with having less brown fat

but increased obesity so of course we we

don't know yet whether a brown fat

decreases with A's and therefore before

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 sensitive 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 in elderly people some have

a lot especially people working outside

there are studies showing this who

people who work outside do physical work

outside farmers and

um yeah interesting yeah yeah thanks

post themselves to it so they'll just

keep it in that way it's

um and I suppose we should um clarify

for people in case they don't know that

insulin sensitivity is a very good thing

you want that you want your cells to be

sensitive to insulin insulin

insensitivity is type 2 diabetes and is

associated with obesity

um so just a point of clarification

there

uh yeah it's interesting to me I I 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 uh the

outside world

um and there are a few individuals at

the the gym who are they're not

particularly large or muscular

um but they are incredibly

um lean and their posture is great

presumably from the musculoskeletal work

um and they they're in their 70s and 80s

I mean it's remarkable right and um 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

they're they're they're

um they're fit they're they're clearly

of that look and you see this written

outside the gym too of course for people

that look like they've done a lot of

physical labor their whole life yeah

they're just moving a lot they have

strong hands and features and they're

um and they're not necessarily except

aggressively 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

what did you grow up doing you know and

I would say and obviously I haven't run

statistics on this but

more than 75 percent 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 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 uh

shock type thing like deliberate cold

exposure yeah I think that is a really

good question because how how also why

do we have this tissue then if it's if

it has to be extreme then you can

question what 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 to cold so

cold is the most potent stress or

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 a hand actually

just to cold water so Studies have shown

um that if you just put your hand in

cold water not that you're going to

going to do that all day or or every day

or anything it's not it's 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

t-shirts that's why also we were just

talking about well people who works

outside or move a lot or get out in and

out of it like changing the temperature

of the body all the time they will have

more Brown fat and activating that is

going to keep your metabolism higher and

your insulin sensitivity is that it has

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

vests also Studies have shown this for

10 days it's gonna also grow your 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 a wind has

also shown to activate your brown fat or

if you don't want to 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 and

then you will activate your brown fat

and you will grow your ground fat so you

have more of it so this is in very nice

studies

um

from Hansen Adele from 2017 showed that

a group of subjects who slept in a room

at 24 degrees and then they made this

Pet City scannings 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 duet on and

they were still had clothes on when they

were sleeping so they're under a

covered yeah yeah the subjects were

sleeping

one month had increased is insulin

sensitivity the next month they stepped

at 24 degrees they measured this again

and then they had decreased actually a

little bit and then they slept at 27

degrees so quite warm room actually for

for the fourth month um and they saw a

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 coal you

also get a little bit adapted to it but

that's because the brown fat

um has grown these more mitochondria in

the cells so these small energy Fabrics

that's going to activate the cells and

that's going to take up glucose and fat

from the fatty acids from the

bloodstream to keep the thermogenesis up

and that's going to clear up some sugar

and it's going to click so in the in the

bloodstream and some 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 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 are

have courage for it you can go out and

expose yourself in a coat plunge

um cold showers is also going to do the

trick so you can do different variations

of this just exposing yourself to

various temperatures it's going to

activate the brown fat because it was

involved to keep us in a perfect

homeostatic balance regarding

temperature so to Keep Us Alive

incredible uh I want to just get a

clarification around this 19 degrees

Celsius room that they're sleeping in so

they're under a comforter a duvet and um

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 uh the the increase in

brown fat that was observed is that is

that a reasonable expectation I I think

so yeah because it's you have so many

co-receptors in your face so it's

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 in my studies just to see how

well did they respond to cold water so

it was a four degrees Celsius cold water

for four minutes and then I just met

your blood pressure on 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 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 in your around your central

nervous system

um and and the biggest Depot as you

mentioned before is up here under the

clavicular bones so

um 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 here and it's not

very feasible for people to go home and

do this don't because it takes a lot of

practice I can tell

um but we measured the brown fat with

this um and and I could see that after a

few minutes that the activation was

there an 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 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

called the guy who I worked for at the

time and I'm Harry Carlyle is a very

accomplished physiologist he came from

this lineage I don't know if this

literature is still um discussed much

but it's a beautiful literature

um from Rothwell and stock they were the

ones who discovered um 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 um stochastic movement

um burn up to 18

00 calories more per day than people who

sit more still fascinating incredible

and just incredible

um I don't think that work does gets as

much attention as it deserves publishing

journals like nature so very uh fine

journals but in any event

uh 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 um Dr Carlisle Harry

um 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 yeah because the brown fat

had expanded

um or or added mitochondria or both and

I was perfectly comfortable in that

environment I also got very very lean in

those um 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 it was striking uh what a

powerful effect it had on my entire

system of thermal regulation and one of

the things that I uh also delighted in

when cell reports

um medicine published your study is they

had in an accompanying um press release

that went out to to those of us that

received press releases and it described

a um a saying in Scandinavia which is um

essentially I'm not going to attempt to

uh speak uh Danish even though I have

much of my family is in Denmark I

believe or not from Denmark

um we have a lot of Danes in my family

um I won't embarrass myself by trying to

speak Danish as I did before the the

microphones were rolling but

um that there's a saying that I think

essentially translates to in the fall

when 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

and maybe do you know the saying and

would you be willing to share it only

the swedes and um uh and Danes will be

able to understand

um maybe the Norwegians too if you don't

know it that's okay yeah so I know that

I know the the concept of it because we

say it you should you should wear a less

before winter and and more before summer

so there it is in English so it doesn't

have to be esoteric but okay yeah and

and you're completely right and I think

this is the this is just something that

we know in the Scandinavian countries I

think that we we

intuitively know this but if we just go

back a little bit in history I think

that um around the 1950s the the Russian

government went out and said well we

should do something about the

tuberculosis pandemic or epidemic make

the worse at the this time so that they

wanted to have the the people

um

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 uh also to

to get more resistance to the coal but

also to increase our immune system and

we still do that in Denmark so we we

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 or at least the

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 cool because

they have activated all the brown fat I

didn't understand at that time I must 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 things are crazy they put the

babies outside and problems and leave

them there and then they go inside and

drink coffee on the cafe

well I don't think Danes are crazy I I I

I Adore the date they're amazing uh

culture and people I'm so fortunate to

have family members uh from Denmark but

I did notice so when when we were in

Copenhagen and I know um we we saw you

there uh not long ago that was June

um the water in the harbor was was cold

for even though the Pacific is close to

here which is very cold I was felt

pretty cold but I it was summertime ish

um so people were in summertime mode

right t-shirts and shorts and things

that 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 yeah

um not many people wearing sunglasses so

trying to extract as much Photon energy

from the Sun as possible which I support

uh as everyone knows that's I'm a big

fan of getting Sun but also

um when we did see swimmers

um they were swimming in this cold water

and like it was nothing and their the

range in age of the swimmers was what

was remarkable you saw the kind of fit

triathlete looking types but also young

kids like really young kids and then

people probably in there again they're

they're 70s 80s maybe even 90s really uh

remarkable uh vastly different than what

you see if you go to the ocean here in

Los Angeles or or elsewhere so

um yeah you Scandinavians are on to

something with this I'd like to take a

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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 um and then walk us through

what you did you know who the subjects

were

um what you had them do what you

measured

um in as much detail as you would like

to share because I think it's such an

important you know even fair to say

landmark study because it also explored

not just cold but sauna and the 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 uh

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 who

did the work in detail so um yeah if you

could tell us about your study um and uh

what you did and what you discovered

thank you for the question Andrew I I'd

love to like 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 what

happened before that and human studies

are very different from from my study my

studies you can do a knockout of

something and then everything is like

perfectly matched and controlled doing

humans studies is very far different

from that because people are different

even in the groups so yeah but what we

um

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 and 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 so but

after that I wanted to to do something

new so I looked into the brown fat got

hired in this fantastic research group

where they it's a cell group so they

mostly did cell studies and they didn't

have anyone to do a human study yet

um and um but they really wanted me to

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 sleeping in the cold I found that

particular paper very fascinating and

that was also where

um at that time I was like okay so cold

exposure sure 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 is first of

all it was already done that was one

thing but the other thing was like well

I wanted to to see if we can do it like

some kind of activity so we can have

people move also go and do something do

something together or whatever and and

the code made us think about well what

about winter swimming and it was kind of

like a bit of a joke in the beginning

it's like winter swimming yeah it's

going to activate the brown fat right

but 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 that was already there

so we were just thinking okay so it

should be very potent

um 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 going to do like a more of a proof

of concept study at the beginning of it

because it was like winter swimmers

um most in theory activate the brown fat

right but we kind of didn't really know

with was this kind of stressor 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 but do we know if it does that no

we don't so

um and while this idea was a little bit

fun fun at the beginning and 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

um let's go with a small number but

enough to see um a difference between

the groups so the power calculation of

that study is done on what we know from

Pet City scannings of the brown fat so

that's the main outcome of that of

course so

um and we wanted to go a little bit

smaller on the numbers of participants

because we wanted to dig a little bit

deeper into the different mechanisms and

also redo some of the the days so I

really wanted to do that to see if I can

replicate also the findings and that's

going to take a lot of a lot of funding

but it's also going to take a lot of

time to do it

um so the proof of concept was just

going small but looking at different

mechanisms we also took

um 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 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

um at all and I would say I was a bit

afraid of the cold myself a bit of a

cold uh 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 income

completely temperature neutral and 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 under Jetty they kind of

joked about is they come on you need to

try this you cannot study this um unless

you have tried it

and I was like haha very funny of course

I can do that

but I couldn't I 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 you and your

muscles hurt the day after right you 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 um on rare occasions well I should

just a full disclosure I 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 um and we'll talk about why

that's probably not the best idea but um

and I've been doing it for some years

now

um on and off uh but so just full

disclosure I'm a devotee

um and I have family members that uh

hate the the cold but have gotten into

it and 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

have 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 gasp 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 it's far

easier to to push through

um but when you say that it was really

uncomfortable do you mean the experience

of getting in or you also felt lousy

afterward yeah it's 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

with the group and actually my husband

was there as well because I I really

wanted someone I knew

um coming along because it's very normal

if you haven't done this before you feel

a little bit anxious about it and this

is jonon studies as well because blood

pressure and heart rate goes up in in

those who are new to this kind of

activity so um 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 nutrients

minutes going in your brain and you feel

more positive you feel I feel invigorate

I had so much energy and that like I 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 3 three dips to 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 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 to get

that energy and to get that positive

feeling and and I think that that is

also why I 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

um 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 long time well so maybe

they were like 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 like 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 community

research subjects dying either because

if you're not adapted I mean the people

you know 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 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 um I

found out if if I want to have this

protocol get through ethical committee I

I really needed to go like very like

Sleek with the not too long and and make

sure that they were also very healthy

and and to get approval of course of

this study

um but what I did was to 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 I wanted to do like a proof

of concept where they were already

adapted to the cold and then compare

them to a match control group who were

matched on

um on you could say diet so whether they

vegetarian or not

um and one of them worse in each group

uh also they weren't all vegetarians no

no no just one in each group yeah it's

gonna say with all the amazing fish and

meat in uh in Denmark I'd have a hard

time being a vegetarian no the breads

are amazing the fruits and vegetables

too but okay so there were a couple

vegetarians in each group yeah one one

in each yeah okay and then I'm

vegetarian I have family members of

vegetarians so I've just poking fun yeah

yeah but they were they were matched on

different things so what we usually

match the mono is also BMI

um which shows 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 yeah interesting yeah I

think it's interesting uh a deserved

study yeah yeah why actually I think

it's interesting because women are also

smaller so in size and mass right but

they also have

um a lower peripheral temperature

especially on hands and ears and is that

right that's that's documented that what

women do run colder than men yeah and

physiologically I didn't say

psychologically no no no we won't we

won't go to the psychological

yeah something else that's a different

podcast yeah

so women are just colder physically

so on hands and ears it's measured on

that

um and and 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

they that could be an explanation for

the colder hands for example

some comfortable state is also different

between genders so men are more

comfortable at 22 degrees Celsius and

women are thermal comfortable at 24

degrees Celsius and this is the

thermostat Wars of home have been now

validated

two degrees Celsius by the way prior to

um starting recording uh I made the

executive decision that we were going to

go with Celsius throughout the podcast

um because the majority of the world

uses Celsius so for those of you that

think in Fahrenheit

um the internet is your friend in making

those conversions so we're sticking with

Celsius so men tend to be Thermo

comfortable at 22 degrees Celsius women

at 24. okay interesting explains a lot

about like also 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

it's really it's I'm on both sides here

I understand the men we understand the

women but it's 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 man it

was just to see to eliminate uh all the

confounding factors which could have an

impact on on our results so

um that was one of the reasons

um but also because we yeah so women

have have more Brown fat than men and

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 a group just a

control group and then and a group who

will always winter swimmers so I

recruited winter swimmers who have been

swimming for two to three seasons

um 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

um how much do you how long do you stay

in the water and I monitored how long

did they didn't stay in the water and

recruited based on

um that they only did like two to three

times per week it seems reasonable for

for Denmark at least to do that and they

stayed only in the water for one to two

minutes so the coastal subsides very

quickly and you will get this activation

of your rest and digest system which is

your parasympathetic nervous system so

the the other branch of your other

enormous nervous system and you get that

activation because you submerged 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 the cons Assumption of oxygen

also in your body and that's going to

slow down your heart rate could I pause

you on this because 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

um 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 want

to 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 this is a start obviously more

and more posts about this so um could

you just touch on the what the dive

reflex is and why it act perhaps

activates the parasympathetic response

this calming response

but also the diving reflex is activated

when you submerge into cool water

um even just to the neck yeah or I

thought you had to get your face under

I'm not 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 uh that

diving response as soon as you go

underwater with your body

um so you don't have to do it with your

face as far as I understand I could I

could be wrong though

um yeah so when when you activate your

diving response you will slow down your

um your oxygen consumption in your body

and that is because the body tries to

preserve

um oxygen so you will not get

hypothermic too fast so it's kind of

like a survival system in your body

um so this survival system is very

um important for us of course so that

would be activated and because of that

you will have to maybe one minute or so

I'm that can be precise on that because

I maybe it 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

um and that's going to activate for

example something like serotonin in your

brain which is like also good for mental

balance and people feeling in mental

balance afterwards they after they go up

you know so that is like measured on a

questionnaires and also measure like 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 of that yeah

so you had so you observed these winter

swimmers who are done this for a few

seasons yeah 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

um climbing down a ladder or jumping

into the water up to their neck yeah

climbing yeah okay climbing down a

ladder into it because it's done

Outdoors what a fun study to do my

graduate thesis was done under

fluorescent lights with no windows in a

in a building that uh 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 um not something

required to do a PhD by the way but um

they're climbing down the ladder yeah

getting it 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 to do this

two to three times per week and for each

time they go each day they go they take

three rounds off 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 yeah

um 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 yeah then back

into the cold for a third round yeah

back into the sauna

and then then they're ending and then

back into the cold again and then ending

on cold yeah and uh and we'll talk about

why it's important to end on cold the

so-called sober principle

um how cold was the water in this

particular given average because I

realized it's outdoor winter swimming so

it's going to 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 could do for free

going out in nature and use that and

also have the nature like it's very

healthy impact on us it lowers our

stress 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 like from

October to April and it's like it starts

at 12 degrees I think it's around 12 to

12 degrees Celsius and the water and

then it goes down to two degrees in on

average in January and then up again

um so it's within the spectrum of very

cold water I would say from around 15 15

degrees Celsius and down but it was

actually not colder than like two to

four degrees in in on average when it

was the coldest so it doesn't have to be

that cold to be good enough and and

enough to activate our metabolism

um and what time of day are

um the participants doing this cold

sauna alternation so I think they did

this uh throughout the day so I didn't

control whether they wanted to go in the

morning in the afternoon or in the

evening at that time where I set up this

study I would 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

give to people is to do it when you have

time it's not if 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 are where you can do it and

then then try out if it's going to

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 I can't do

that and that's because the coffee

exercise cold water and immersion is

going to activate your sympathetic

nervous system you haven't increase in

stress response in your body and and

that's going to 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 um that's that's the only thing

so I just told them to do this if they

can during the daytime

um and that's primarily what they also

did and then uh all along you're

measuring Brown fat by way of this

infrared uh camera right

um so what did you observe in terms of

changes in brown how quickly did that

occur and um and then I'd like to ask

also about sauna a bit more because

earlier you mentioned that you can

activate round fat with sauna as well

with heat surface of the skin

um

how long did it take before you observed

significant increases in brown fat and

was it increased density of my brown fat

or distribution was it you know 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 and I didn't

mention this before but besides

measuring

um temperature as an outcome for brown

fat activity we also did pet MRI

scanning of the brown fat so this is

like the the golden standard for

measuring Brown fat and it's not very

feasible for normal people to get an and

a pet a CT or pet MRI a scanning of the

brown fat is super expensive

um so we had both uh to see if we could

have like a continuous measure of brown

fat in humans because that was already

not not out there so I wanted to see

during both the experience governmental

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

City scanning or the pit MRI scanning

was to see upon code activation

um stimulation for some hours do we have

activation can we see the brown fat in

this subject and also during Thermo

neutrality or thermal comfortable State

how is that activated in each of the

group of course ah so you want to see

how comfortable people were away from

the cold water and sauna just had

different temperature environments is

that right yeah so I also measured that

how comfortable are you I had 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

thermal comfortable day that had a whole

day where I just kept them Thermal

comfortable to see do they activate the

brown fat if they're just completely

thermal comfortable as good as we could

get with that because you were asking

people

um on a scale from one to ten and five

being thermal comfortable where are you

on the scale so one would be very cold

and ten would be super burning hot

um yeah and so that was the way to like

try to figure out how do they actually

feel also during their studies they also

measured a Electro myography so of of

muscles to see do they shiver during the

cooling day and sometimes people shiver

before they know they're really

shivering so I had interesting yeah so

our conscious perception of shivering

might not be the best readout of shiver

yeah well you if you also get adapted to

the cold water you will have a less

shivering there will be less vigorous

they will be very small so you wouldn't

probably know that you are shivering

because this 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 a dead

thermogenesis going and compared to when

you're completely new

uh to code water exposure 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

um 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 they

they perception their perception of the

cup was pretty similar in in the in the

groups and we could see that the the

activation of the the muscles that we

measured on

um were different and more pictures in

the control group were the subjects

incentivized to be in the study were

they paid or anything of that sort of

they just happen to like doing uh cold

and sauna and so that's why they did the

study

um well they got paid a little bit for

it but not much and um that's how we do

this sure I was just curious yeah yeah I

was just curious there might be some

folks that Wonder so so what did you

discover in terms of changes in brown

fat insulin resistance or insulin

sensitivity rather and um metabolism so

what we we saw was we had this kind of

different measures to see what to try

and unreal what what's actually going on

when they are already adapted to the

cold water compared to a control group

who was matched on on various parameters

we 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 or two

cooling days and one thermal comfortable

day right so I wanted to measure insulin

when I just they were fasting meaning

that they hadn't eaten in eight hours

before the study day

um and they were completely laying still

not moving just in a bit and we measured

insulin during the experimental day just

to see how what level are they on and we

could see that the the winter swimmer

had lower production of insulin and they

also when they had an glucose drink 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 that

wouldn't that would like ruin maybe the

study so we test for that and see if

they have like a normal curve so what

was this seeing that was that the winter

swimmers had a faster glucose clearance

in the bloodstream so after two hours we

could see that they had a lower level

and it went 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 you want what we all seek

right you know excessive insulin is bad

insulin being a um more or less a

chaperone for blood glucose

um can do all sorts of other things as

well of course but

um and having high blood glucose

obviously terrible yeah for cells

especially brain cells I don't think

people realize how toxic high blood

glucose is having high glucose if you

want to kill neurons you make you make

their uh put them in an environment

where there's too much sugar

um oh yeah very yeah very neurotoxic I

mean that's and their mechanisms like

insulin that buffer that we keep you

know keeping blood glucose in a

reasonable range so that

um that doesn't happen I mean I think

that's why people will go into

insulinemic shock

um hypoglycemic shock is also possible

so that range in which neurons are happy

is not a it's not a tremendously large

range incidentally the range in which

neurons are are

um happy in surviving uh 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 um very interesting yeah

we're thinking about doing uh an episode

on um uh sort of survival of the brain

after death kind of things which

actually happens you hear about these

people who are declared dead and then

come back and there's actually now a lot

of crowd preservation type approaches

for that this is uh anyway we risk going

into the the uh the esoteric now so I'll

steer us back to our discussion about

your study but

um 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 three to two or three

times a week

what were the thresholds that you

discovered were important for getting

these positive changes in um

such as reduced blood sugar or clearance

of blood sugar

um being more efficient uh reduced

insulin improved Brown fat distribution

and density

um 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 laauken at L

for example they published this very

amazing paper in 2015 and some results

from this long cohort study where they

show that that up to 30 minutes in the

sauna was healthy and they you 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 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

that's per week 90 minutes per week 90

minutes per session now recession yeah

per session if we

um

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 that 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

2 000 sauna bathers where they have full

of these for 20 years they see that a 30

minutes position 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 per session per

session and it's not 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 a message to

to 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

and per session but go up to 11 minutes

per week in total and for the sauna my

study showed uh 57 minutes in total two

weeks and if we also then divide it out

on these two to three days and two

sessions each day correspond to 10 to 15

minutes so it's a low threshold but I

think it's it's good to have that to

maybe we can aim for that if people need

to have something to to aim for and I

think and I think it's really good to

have that because then you you don't

have 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 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 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 um to

an hour but divided into maybe three

20-minute sessions or so you know um so

one doesn't have to be perfect as long

as you get a beyond that threshold but I

I wonder something which is

it the case that if somebody said oh you

know 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 yeah

you're getting very cold and you're

shivering but you're one is not getting

the autonomic stimulus that they want I

guess I could liken this to um 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 um

in fact probably quite the opposite

um but if that were the case then it's

not simply the total amount of exercise

but dividing up the the the sessions

into little bouts where every single

time it acts as a stimulus that seems to

be the key here

um this is very important

um because having watched the landscape

of this on social media but also in

books and generally

um 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 yeah 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 uh

um you know challenging to most people

than finding a full morning to go you

know spend there

um but I've never really heard it

articulated that the longer sessions

might not be beneficial it might

actually be detrimental

um

that's very important uh were there any

other observations that you made

um that did not make it into the paper

or that were kind of in the the margin

notes I mean in terms of psychological

benefits

um 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

um but one of the things they remarked

in the paper was that there were a lot

of psychological changes improved

buffering against anxiety

um they even the men and women in that

study reported one of the significant

effects was um significantly improved

sexual satisfaction of course they

didn't tell us what that meant for these

subjects but so we won't go there but

but a number of subjective improvements

was there anything that you observed or

took note of in in your study that

perhaps didn't make the main abstract

but that we should be aware of uh

yeah there was some um and I'm I'm today

I regret that I didn't measure on sleep

for example I I frankly didn't really

think about that when I I when I

designed the study

um so we were very

um much occupied with the metabolism and

kind of had the thought maybe this could

impact a Sleep Quality

um and I wish I just if I 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

Monies to just two mornings actually and

we measured on

um but the winter swimmers

um

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 the

brown fat on a day and night so if

actually two days and two nights and

they told me that they didn't 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

um and the winter swimmers is so they

have a really good sleep so it's like

and in general they also say we 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

um which would could be fun to do in the