Feel Better, Live More with Dr Rangan Chatterjee - The New Science of Cold Exposure: Reduce Stress, Boost Immunity & Increase Resilience with Dr Susanna Søberg #322

Episode Date: January 4, 2023

Cold showers, icy plunge pools, outdoor swimming – are you a fan, or does the very idea make you shiver? Today’s podcast is all about one of the biggest wellness trends of the past few years: cold water immersion therapy. My guest is Dr Susanna Søberg who is arguably one of the leading researchers on the topic. Susanna studied at the University of Copenhagen, looking at metabolism and the role of brown fat. Her research on the physiology of deliberate cold and heat exposure is helping to back up what many cultures have known instinctively for thousands of years – changing our temperature is good for us. Her new book Winter Swimming: The Nordic Way Towards a Healthier and Happier Life is a beautifully illustrated volume, which looks at cold-water traditions around the world and shares what incredible benefits they can provide for our health and wellbeing. In this conversation, Susanna talks us through the many physical benefits, from increased metabolism, immunity and lowered insulin resistance, to the potential to reduce excess weight and ease muscle and joint pain. The key player in all these benefits? Brown fat, a type of healthy fat stored around the spine that acts as our body’s temperature regulator, boosts metabolism and can even aid blood-sugar response and weight control. The more we expose ourselves to the cold, the more brown fat cells we have. So it’s a case of use it or lose it. There are also incredible mental health benefits from engaging with the cold. The very act of pushing out of your comfort zone and braving the cold can give you a sense of confidence. It releases mood-boosting hormones and exposes us to a form of ‘healthy stress’, building our resilience to modern life. It’s also the ultimate in mindfulness – a sensory experience that takes you out of your head and into your body. In 2021 Susanna published research setting out the minimum amount of time that we need to spend in the cold to receive all these incredible health benefits. It’s now been dubbed the Søberg Principle and it’s not nearly as extreme as you might think. Even just a cooler blast at the end of your shower is a very effective place to start.   I really was delighted and honoured that Susanna came over from Denmark to record her first ever long form podcast. Whatever your view on the cold – whether you embrace it fully or whether you think this is a trend that is not for you – I really think you are going to enjoy listening and I’m pretty sure that after listening, you may well be tempted to give the cold a go. CAUTION: If you have uncontrolled hypertension or heart disease it is not advised that you start practising cold water immersion. If you have any doubt at all as to whether you are fit enough to give this practice a go, please consult a qualified healthcare professional. Thanks to our sponsors: https://www.athleticgreens.com/livemore https://www.boncharge.com/livemore https://www.vivobarefoot.com/livemore Show notes https://drchatterjee.com/322 DISCLAIMER: The content in the podcast and on this webpage is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your doctor or qualified healthcare provider with any questions you may have.

The healthy brown fat is actually the temperature regulator that we have in our body. And if we don't get exposed to different temperatures changing on our skin, then we are not using this organ in our body. This organ is not only controlling our temperature, it's actually also helping your metabolism. We can definitely see in my studies and also in humans that if you don't have that much brown fat, that you will have more obesity, more lifestyle diseases, higher cholesterol levels and higher blood pressure. Hey guys, how you doing? Hope you're having a good week so far. My name is Dr. Rangan Chatterjee and this is my podcast, Feel Better, Live More.

feel better, live more. Hey guys, how you doing? Happy New Year. This of course is the first episode of 2023. Really excited about the guests that I have lined up for you this year on the podcast. And I know, especially at this time of year, the podcast receives many new listeners. So if this is your first time, a very warm welcome. Today's podcast is about one of the biggest wellness trends of the past few years, cold water immersion. Basically, deliberately exposing ourselves to the cold. This could be outdoor swimming, it could be icy plunge pools, or even just a little blast of cold at the end of your relaxing warm shower. Are you a fan or does the very idea make you shiver? Well, my guest today is Dr. Susanna Soberg, arguably one of the world's leading researchers on this topic.

Susanna studied her PhD at the University of Copenhagen, looking at metabolism and the role of brown fats. Her research on the physiology of deliberate cold and heat exposure is helping to back up what many cultures have known instinctively for thousands of years. Changing our temperature is good for us. Her brand new book, Winter Swimming, The Nordic Way Towards a Healthier and Happier Life, which looks at cold water traditions all around the world and shares what incredible benefits they can provide for our health and well-being. In our conversation,

we discussed the many physical benefits, including increased metabolism, better immune system function, less insulin resistance, as well as the potential of the cold to help us lose excess weight and ease muscle and joint pain. We talk about brown fat, an incredibly important type of healthy fat stored around the spine that acts as our body's temperature regulator and can provide us with a host of health benefits. There are also incredible mental health benefits from engaging with the cold. The very act of stepping outside our comfort zone and doing something hard increases self-confidence and resilience. And it's also one of the ultimate mindful practices that immediately takes you out of your head and puts you into your body. Now in 2021, Susanna published research setting out the minimum amount

of time that we need to spend in the cold to receive all these incredible health benefits. It's now been dubbed the So Big Principle, and you'll be pleasantly surprised to learn it's not nearly as extreme or challenging as you might think. I really was delighted and honoured that Susanna came over to my studio all the way from Denmark to record her first ever long-form podcast. Whatever your current view on the cold, whether you embrace it fully or whether you think this is a trend that is simply not for you, I really think you're going to enjoy listening, and I'm pretty sure that at the end, you may well be tempted to give the cold a go. Now please note that the content in this podcast is not medical

advice. If you have uncontrolled hypertension or heart disease, it is not advised that you start practicing cold immersion, and if you have any doubt at all as to whether you should be giving this practice a go, please consult a qualified healthcare professional. And now, my conversation with Dr. Susanna Sobel. Susanna Sober. I've been looking forward to talking to you for many months now. And I think over the past few years, there's been a growing awareness of the benefits of deliberately exposing ourselves to the cold. There's been lots of anecdotes. I think Wim Hof has absolutely popularized this across the world.

What I find interesting with you though Susanna is that you've actually gone and conducted some proper scientific research to actually help us identify what is really going on when we expose ourselves to the cold. So right at the top, given how reluctant many people are to expose themselves to anything cold these days, can you make the case as to why people should do it? Yeah, there are so many reasons why people should do it. So there is so much going on in the body when you go into the cold. So there's definitely physiological reasons why people should do this because it can actually benefit your health right away. There's like this acute response that you will benefit from, but also on the long term.

So this could actually prevent lifestyle diseases. And also on a mental state, you can say that you can use this as a way of increasing your stress threshold, actually, and getting more confident, actually. That is one of the things that I discovered later on and not from the beginning. So I started my research in looking into what happens in the body. And since then, I would just work my way around what else is going on. Yeah. I think you've really touched on a few important things there for me. Like when I think about the cold and why I, why my patients, why the general public should consider, you know, intentionally exposing themselves to that cold, I kind of put these benefits into three different categories. The physical benefits, so things like your metabolism, potential benefits with weight loss, type 2 diabetes, you know, the immune system, things like brown fat, which we're going to talk

about, joint pain, all these things. Then I think about our mental health and well-being. So our resilience, mood, anxiety, depression. And then I think about athletics and I think about recovery and endurance. So it's quite incredible that one modality, one thing, cold exposure can potentially have so many different benefits, right? Yeah. Yeah. And you need to think about why is actually this one thing, why is it that it can do so many good things? Why is it that we cannot get a pill to do exactly all those things? It cannot happen. We don't have that. But you can go into the cold and you can use it in very much, very different ways. So if you have pain, you can go into the cold and you can use it in very much, very different ways. So if you have pain, you can go into the cold and you will have less pain and that will last for the day at least.

And if you are in a bad mood, you can go into the cold as well and you will feel much better. It's just, you can use it in so many different ways. You can use it for recovery, as you just said. And I think that it's very difficult to find something else that is that great. It can do so many good things. You can have so many reasons to go. And there is always something that the cold can repair for you in your body. So it seems like when I started my research, I was pretty much looking into the brown fat, which you just mentioned.

But when I met people out there swimming around and I asked them, why do you use the cold? And every time I got a different answer and every one of them seemed to have like one problem with this or one problem with that and help in different ways. So it seems like maybe from an evolutionary point of view that this is something that we involved in, of course, but it's also something that we as human beings need to reset our body in every way. So it's like going into the cold, that readjusted just everything in our system, our mood, our physiology. So if you have pain, that will go away. So it just seems like it's going to do

everything good for us, no matter what kind of pain or what kind of issues that we have. Yeah. You say pain there. And when I hear the term pain now, I think of physical pain and emotional pain. And it's something I've been thinking about for a while, but I spoke to this wonderful doctor a few weeks ago on the show called Dr. Howard Schubiner. And he was talking about a lot of the research he's done on chronic pain. And he was sharing how the body will have pain

to a physical injury, but also to an emotional injury. And it shows up in the same part of the brain. And I think it's really great to connect that to the cold because as you say the cold is having these physical benefits but also these mental and emotional benefits as well yeah but it's also just our body and mind is connected of course so if we go into cold, it's going to change something physical, right? And that will, of course, also connect with our brain and that's going to change something in the brain. So the brain, when we go into the cold,

there will be a release of neurotransmitters, all these good chemicals in the brain, and that will float around in your body as well and all these hormones. So it's going to connect how you feel. So if you can take away the physical pain, that is also what is going on happening in the mind. This whole field of science versus anecdotes is really interesting to me. And one of the reasons I was so excited to talk to you

is because there is a lot of anecdotal knowledge and wisdom about the cold, but I don't know anyone who studied it as much as you. And it's really amazing to say, yeah, humans have kind of known this for hundreds of thousands of years, but you're now showcasing with your science what exactly might be going on. So I definitely want to get into all of that. I want to make this super practical for people as well. But Susanna, I thought near the start of this conversation, I really want to address the issue that many people have, which is, I just don't want to get cold. Like it's not for me. If I speak to my wife about a cold shower or doing some cold immersion, she will point blank refuse. That's not for me. You know, I'm not good with the cold. So can you just speak to that at the start here?

Yeah. Well, that is definitely the main thing. The thing is that in our society, we are now in a time where we don't want to get uncomfortable. We are so used to seeking comfort all the time. we don't want to get uncomfortable. We are so used to seeking comfort all the time. And we want that. We want everything to be warm. We want everything to be easy, easy food, fast food. We want everything to be right at our hands. And we have taught ourselves that the cold is not something that is useful for anything. And I kind of understand why, because, well, we haven't really for a long time known what does the coal actually do for us, is beneficial for us. It's quite new that, as you said, that the science has catched up with this intuitively

good thing to do, right? So it's actually brand new that we know that this is good for us. So that is why we're sitting here, right? We're talking about what is the benefits of this on a scientific level. But for thousands of years, we have known intuitively that this is good. So if we go back to Hippocrates, let's go back to the ancient times where they already knew that this is really, really good. So he said that using cold and heat, actually, for these ancient philosophers from that time said that you should go into the cold water, you should go into the hot water, because it's good for your cardiovascular system.

And it's good for your heart. So they already advised it back then. And people were doing this all over. They called it thermalism. So they were doing this everywhere. And it was something everybody thought of as beneficial for them. And there was no really proof of this. But since thermalism and until maybe today, there has been wars going on. And also the Titanic disaster also kind of put a shadow over the cold water because then people found out that if you drown,

if you fall into very cold water, you get hypothermic and you would die within 30 minutes. And that was not very good for the cold water and its reputation. So no scientist at that time wanted to pick up this basic science and say, well, we need to study more on the beneficial sides of this because it really had this dark history now. So then we actually, not until, if you go back in the science literature,

you will find old physiology studies, but these are not that old, actually. They go back to the 70s or maybe the 80s. And then up until today, there are more and more studies on the the you can say the physiology of the cold but up until then people didn't want to really touch it because of all these accidents and and stuff that was going on back then but this is not this is of course accidents which we shouldn't compare to doing deliberate cold exposure so that is why

we have catching up now but this was one of the questions I needed to have answered for myself. Why is it that we are so behind on this research? Why is it that I can come today and tell you about cold water exposure and brown fat and the beneficial side of this? And we are in 2022. So I think it's a bit late, but we are picking up. We are getting back to the thermalism. Yeah, it's interesting to hear that historical kind of narrative.

I didn't know a lot of that, actually. And when you mentioned the Titanic, the first thing that came to my mind as you were saying that was that we don't not get in a car because there are car accidents and in a multi-car pileup on the motorway a lot of people may well die or get you know seriously injured yeah but we do it anyways but we still do it yeah we go no I'm still gonna drive or take a car or a bus here right so it's it is fascinating and i think i'm i'm really interested always have been in terms of why a lot of the stuff that the science is now showing

has been practiced by humans from all different parts of the world for years like you mentioned hippocrates hippocrates also said let food be thy medicine and medicine be thy food. And now there's a growing recognition in the last 10, maybe 15 years that, oh, the food that you eat can actually be used in a medicinal way or a non-medicinal way. And traditional Chinese medicine for years has been talking about that different parts of the body are more active at different times of the day. And, you know, I think Western science looked down on that for years. And, you know, in the last 10 years with chronobiology, and as we're seeing, oh yeah, they were right.

Yeah. So I find that really, really interesting. Yeah. Do you think it's possible for everyone to start to embrace the cold? Or do you think some people, like my wife, for example, if she says the cold is not for me, is that something they should, you know, because the first time they go in, they're struggling. So they don't want to do it anymore. Is that a good reason for them not to do it at all? No, no, not in my opinion. Because I mean, the more they reject it, the more they might even need it, actually.

Because you need to go into the cold multiple times to get at least just a little bit used to it. So in the beginning, it will definitely be very hard. And that is something that you need to push through. You can use it as a way of also, it's a kind of training, you can say. Just like going to the gym, your muscles will be sore. It's a kind of training you can say, just like going to the gym, your muscles will be sore and going into the first cold shower or cold plunge will also hurt you in a way because the cold pain is there, right? But for every time you go to the gym or every time you go to the cold, you can see that as exercise, not only exercise in the cold for your physiology, but it's also a mental kind of workout that you're doing. You're pushing yourself to the uncomfortable state. And every time you do that, you get a little bit stronger, not only in your cells, but also in your mind. So every time you can do that, you push yourself a little bit, you get more confident. Next time I can do this again.

So going into the code, this is in our DNA. I mean, we evolved in the cold. So if people say that, well, the cold is not for me, you can tell your wife, well, you're involved in the cold. The cold and your ancestors did this all the time. This is the reason why we are here. So if they can do it, we can do it. And they were healthy because they were living out there. The cold was just something that they embraced every day. And they were chased by lions and hunting all the time. And then they relaxed. So they also had this, you can say going into the cold, but then they also relaxed. So this is called the eustress. So this is the healthy kind of stress yeah so you stress your body in a very good way but then you also pause so you have like your calm maybe rest of the day or you're not too

stressful at least but this modern society we're doing something completely different we have turned this upside down so now we are stressed all day and then we go do something that will also stress us and we don't find the peace in between so we have this kind of like drip full all the time all day of stress which then eventually would be chronic stress but going into the cold is uh it's very stressful it's it's very potent you know the temperature but it's very um it's very useful because you only do it at that time and then you're calm afterwards. So we need to learn what is actually stress. It's such an important point. You know, you mentioned, I guess, comfort. Comfort is killing us. You know, as humans, we've always been wired to make things easier, to seek out comfort. But until

recently, even though we're wired that way, we would have been exposed to discomfort pretty much every day. I guess that the extreme of that is now where, I don't know what it's like in Denmark, but certainly here in the UK, and I know in America, you can literally sit on your sofa and on an app, order whatever food you want and have it delivered to your door 10 or 15 minutes later. And often that food isn't, let's say, the most health-promoting food that we could be eating. That is an extreme version of how, you know, acquiring food is something we would always have required to put some effort into, to hunt or to gather, right? And then even to cook it. But every little bit of discomfort is being engineered out of our lives. Movement, escalators, lifts, right? All these things. Now you don't have to move anymore.

You can still function. I think the cold is just a brilliant example of that. I totally agree with you that I think many people who struggle with the cold probably struggle with it because they're not exposed to it. Now I understand some people have got thyroid issues, which can change your cold tolerance. So I just want to be clear on that. I think for many of us, we've narrowed our experience of life. Everything's, you know, let's talk about temperature. We've got heating or air conditioning at home and in the car and in the office. So we're never being exposed. So our whole world is coming inwards, which is why presumably we have this low tolerance to anything, low tolerance to stress, low tolerance to heat.

And I absolutely agree with you that regularly with these controlled doses of exposure to this form of stress will little by little start to widen that window. So, you know, over time, yes, you're more tolerant to the cold, but you'll also be more tolerant to the stress that you experience in everyday life. Yeah, exactly. Yeah. I love that. Yeah, exactly. So taking the cold out of your everyday, which we have done, we have warm clothes on. We have very warm rooms. We sleep with big pillows and blankets and everything. So we are not exposing ourselves to something that we were actually born to do, to be involved in different temperatures. And we actually know this from a very special organ that we have in our body. Nobody knows about this organ. It's not something that we have explored that much, but it's called the brown fat. So the healthy brown fat,

I call it healthy and it is healthy, but I just want to outline that it's healthy. So the healthy brown fat is quite opposite to our white fat. And this special little bit mystic organ that we have is actually the temperature regulated that we have in our body. And if we don't get exposed to temperature, different temperatures changing on our skin, then we are not using this organ in our body. And many people were like, well, do we need it then? Because if we are not exposed to any different temperatures, then we might not need it. But then actually we have found out that this organ is not only controlling our temperature from the inside, it's actually also helping your metabolism. So it has a huge impact on our health.

And we can see in studies that if people don't have the healthy brown fat, we see that they have more obesity. They have a larger, higher BMI, but they also have type 2 diabetes. So there is definitely a correlation of less brown fat and being overweight and having type 2 diabetes and have cardiovascular diseases. And this is also increasing, of course, with age. But we also see that if you have brown fat, that your energy expenditure goes up and that you will have lower blood pressure. You will have less obesity and not having type 2 diabetes, for example.

So people or scientists from, I think it was about the millennium actually, so it's quite new that people are doing all this research in it. But we found out that if we can activate the brown fat, it will not only increase our temperature from the inside, but it will also use our glucose and it will use our fat from our bloodstream as fuel. And this is really good for us because then we are cleaning up some of the stuff that we have put in and sitting on our couch and eating all this very comforting food. So we have too much of that. That is why we have all these lifestyle diseases. But the brown fat is not being used

in our society because we are so comfortable all the time. So if we can get cold on our skin, we can activate the brown fat and it would do that immediately actually. So as soon as you get in the cold or go outside actually just in a t-shirt, you will have cold receptors on the skin sending a signal to the brain in the temperature regulating center and that will release norepinephrine or adrenaline, you can also call it. So this stressor will activate your brown fat cells, which will then take sugar and

fat in as fuel to generate heat. So you actually get warmer by going into the cold. So when your wife says, I don't want to do this, not for me, because I'm so cold. I would say, well, if you just do it a little bit and you just keep practicing, tell yourself that this is really good. Susanna's study have shown that winter swimmers get warmer by going into the cold. Then she will thank me at some time. I hope. Yeah, I hope so. Well, she actually is the producer on this show. So, you know, let's see when she hears this, if she keeps it in or chops it out, but I'm sure she'll keep it in. Susanna, what you said there was fascinating, right? Let's just rewind a second. You mentioned healthy brown fat. So by and large across society,

the word fat has negative connotations. For many years, people have been fearing fats. They don't want fat on their body. They don't want fat in their food. Now, regarding diet, that's started to change over the last 10 or 15 years where there's been a recognition that actually some fats are very healthy and certainly health-promoting for the body, whereas certain fats are not. So the narrative around fat when it comes to food and diet has started to change. But I think it's really interesting to hear that even the fat in our body has, you know, for want of a better term, kind of good fats and bad fats, right? I know it's not a perfect term, but this white fat that I think many of us are used to, the fat under our skin,

by and large, I think it's fair to say many people, most people want less white fat. Yes. But you're saying that we should all probably want to have more brown fat in our bodies. And one of the ways we can do that is with cold. Yes. Now, across all ages, what are levels of brown fat like, let's say, in babies, children, adults, as we get older? So that's the first part of this question. You know, how does that change? But I'm also interested, are we as a society losing brown fat because we're in temperature-controlled environments all the time? Therefore, we have no need for it?

So I wonder if you could answer those two parts there, please. Yeah, really good questions. And I think that we definitely need to just talk a little bit about what is the brown fat and where does it actually start? So we are born with brown fat, actually a lot of it. So babies have a lot of brown fat actually on the back., you can say compared to the rest of the body, it's quite a lot actually. And that is because babies cannot shiver when they get cold because the muscles are not developed enough to generate heat. So there are two systems in our body that can generate heat. So it's the brown fat and it's also the muscles. And it's also the muscles.

But the muscles are kind of too slow to actually save us in, you can say, in a dangerous situation where you are exposed to cold. So if you put a baby out on the table without clothes, it would definitely start activating the brown fat immediately. But if it's less than six months old, it cannot really shiver in the muscles. So it's necessary for a baby to survive to have brown fat. Nature knows best. Nature knows best, exactly. But with age, scientists found that it decreases with age. But that also fits with, you can say, the time where we can actually use the muscles also to generate heat in our body. So we don't need as much brown fat as adults as we need

as babies. So probably that is why we get less of it. But what we see is that until the age of 40, most people actually have brown fat. And we also see that you can gain more brown fat if you are exposed to stressors as cold, which will then generate more brown fat. So what we see is that after the age of 40, there is a decline. And it's correlating with obesity and it's correlating with type 2 diabetes and lifestyle diseases. And we don't know really what comes first, but if it's obesity and then less of the brown fat, but it's also about the lifestyle, right?

So if you are not moving, if you're not exercising and you are not getting into cold, you're not stressing your body in a healthy way, you will get more of the white fat, which is on our stomach and our, yeah. You want to get less of that, but you also, unfortunately, the brown fat will disappear. So there's actually studies showing from, yeah, I think it was 2009,

where they showed that people who sleep in a cold room, or people who sleep in a warm room for a month, they measured on these MRI imaging, they could see how much brown fat do these people have. And then they slept in the same, in a room at 19 degrees, so colder at least, not very cold, but 19 degrees Celsius, right? That is okay cold. And they saw that they increased the amount of brown fat, but also that they get more insulin sensitive actually. Wow.

Yeah, so that is just one month. Sleeping at 19 degrees, they saw the increasing amount of brown fat. And there's actually a picture in the book where you can see the brown fat. That is some of my research results actually in there, so you can see where it's located. So the imaging is of the supraclavicular bones where you can see the largest depot that we have. But it's also located down the spine. Everything is just, the brown fat is close to the central nervous system, which makes sense, right? Because the cold is the main driver for activating our brown fat yeah because it

needed to save us as we involved as humans right so we can immediately when we get cold it can be activated and make this temperature control in the body and activate our metabolism because we need fuel to to to fuel these brown fat cells which taking up all this fat and sugar in our bloodstream yeah you know what i love about that that study you know a theme already which i keep bringing up is the reluctance of people to want to get cold i spoke to dr roger schwelt maybe a year ago or so on this podcast and he mentioned some of the research on the immune system and we'll get to that for sure in terms of what cold can do for the immune system, which is really interesting, really impressive to hear, really helpful for people. But you always

get these comments, yeah, it's not for me, you know, the cold. But what you're saying there is just simply sleeping in a cool room. So not a super hot, central heating driven room. Even that alone will increase levels of brown fat. That's probably quite achievable for people. It is. I mean, so many people think that, oh, this mystic new brown fat, you need to get into a cold tub and you need to be there for 10 minutes or something like that. It's very extreme, I think. It's very extreme that you go into a cold and sit there for a very long time. Some people do it for half an hour. It's not, it's not that, that I'm trying to promote at least. I'm just saying

that try to get us, try to get cold in some way. If, if it's a cold shower, then do that. If you like cold plunging, then do that. But you can also turn down the heater in your living room and just sleep very cold. I mean, if I ask my grandparents, they would say, I always sleep cold. I have the window open. And as a child, I was like, why? Why are you doing that? And they always answer, because it's healthy for us. But I was brought up in another, you can say, time where we were trying to get more comfortable even more your grandparents knew it yeah they knew it they didn't need your research they didn't need a science episode they didn't need pub med they're like this is healthy that's just we know it isn't you know funnily enough like we know from the sleep research that cooler rooms promote better

sleep yet as it gets cool I understand people don't want to get cold. I understand. I don't want to be very sensitive. I understand that a lot of people are struggling economically. They're struggling to heat their homes. I do appreciate that. So I want to make sure we're being super sensitive to that. But at the same time, I think there's many of us who are overly heating our rooms. I know the amount of times I've spoken to my patients about, why don't you just reduce the temperature in your room at night? And they come back and say, oh, I went to bed feeling a little bit cold,

but I had the best night's sleep ever. Exactly. But again, we're conditioned away from discomfort. So we go to bed and we think oh it's i need to put the heating on i need to put the heater on because it's too cold yeah you're actually going to sleep better as well yeah exactly i also find it really interesting what you said that above the age of 40 it looks as though we're losing brown fats and then i think to all the public conversations around obesity, metabolic health, type 2 diabetes, and people are talking about the lack of movement in society. They're talking about

how diet has changed and the sorts of foods many of us are eating. And it's easy to put everything down to food and exercise. And we're learning from the sleep research, how sleep deprivation increases your risk of obesity, how you're going to eat more when you've not slept well, et cetera, et cetera. And I think we're learning that it's multifaceted. There may not just be one reason. There's lots of different factors. And you're now bringing up for me, well, what is coming first? Could brown fat be a huge player here? Maybe not causative in and of itself, but maybe as part of the strategy,

like being temperature controlled all the time means we're losing this brown fat. And I think, did you mention it? It's like a furnace. It is. You can call it like, maybe you can call it a radiator. So it's our inner heater. And you can say the thermostat is our brain because the brain is increasing the adrenaline, the noradrenaline, which is going to activate the brown fat. But it's going so quickly. So our inner heater, the brown fat, will get activated as soon as you just get a little bit cold on your skin.

So it's kind of like balancing our temperature. So what we talked about before also, you don't need to get into a freezing cold water to activate your brown fat. And you don't need to be there for a very long time to get any benefits from it. So just getting cold from different reasons will keep your brown fat alive. And what I mean alive is that the brown fat cells, they need to get activated to stay alive. It's like a muscle. You can compare the brown fat to a muscle. It is also another color from white fat, actually. So the white fat is more yellowish and the brown fat has its brown color from mitochondria. So in the brown fat cells, there are these energy fabrics called mitochondria.

And there are more of those in the brown fat compared to the white fat cells. That is why we can activate the brown fat by cold. And that is taking up the sugar and the fat from the bloodstream as fuel. But also you can increase the efficiency of these cells. And one of my hypothesis from my studies was that could we get more efficient brown fat cells, meaning that could we generate more heat from the brown fat cells if we keep exposing the brown fat cells to cold.

Or we increase the amount of tissue that we have with the brown fat tissue. So that is actually why we did this study in winter swimmers, because I wanted to see if something you can say, and nice for some people, at least for winter swimmers, it's nice to go and winter swim. An activity like that, could that be a way to keep our brown fat alive, to keep our metabolism up and keep us healthy? Because I think it's a bit underrated, actually, the brown fat. It is mystic, but it's also underrated, what it's doing for us. But we can definitely see in my studies and also in humans

that if you don't have that much brown fat, that you will have more obesity, more lifestyle diseases, higher cholesterol levels and higher blood pressure. So it's definitely something of a joker, you can say, in the body. But as you said, it works together with all the other things. But it reminds us that if we go out, use stressors as cold to activate our central nervous system and our metabolism, it would definitely, it's definitely an easy way, I think, to keep ourselves just a little bit more healthy.

It's a powerful image that the brown fat in our body is going to start sucking out the sugar and the fat and start burning it. That's a very powerful image. You know, the amount of people across society who are trying to improve their health lose a bit of their weight or more of their weight depending on, you know, their current state of health. know their current state of health and this could be a relatively simple potentially free for many people part of an overall strategy maybe not the only thing they do but maybe as part of everything else you just add this in it's another maybe 10 or 15 percent of the way who knows you know I find that really interesting I'm also fascinated by you, when did we first discover brown fat? Do you know when that was? Just taking a quick break to give a shout out to AG1, one of the sponsors of today's show. Now, if you're looking for something at this time of year to kickstart your health, I'd highly recommend that you consider AG1. AG1 has been in my own life for over five years now.

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The first time we discovered the brown fat was by this scientist who was exploring the physiology of hibernating animals. And he caught up this animal, he found the brown fat, and he was like, well, this is a mystic kind of fat or tissue or muscle or whatever. And he found out that this was activated by cold and that only hibernating animals actually had this. So he found out that the hibernating animals needed the brown fat to survive through the winter because then they could use that as they're in a heater during hibernation, of course. But later on, they found out that, the scientists found out that this is also present in humans and it's also not hibernating animals, which is quite fascinating, I think.

If you look at squirrels, for example, squirrels are hibernating as well. And they go down to two degrees when they're hibernating, which is a thing I find super fascinating that they can stay alive. In such cold. In such cold. And that's because they have brown fat.

And this has been studied, but this is many years ago. But all these studies that scientists have done in this have been like, well, they came to a new wall where they saw, oh, we cannot really go further with this because we cannot get funding. Because now it's kind of like disproving that this is only for hibernating animals. humans have it as well we found out but that is not until the 19th 60s or something where we saw it by by coincidence actually that is quite fascinating that so

many years we knew about this in animals but we were kind of like well we don't need this it's kind of like not not needed for people because we are living in houses now and what is this actually doing it's amazing that that it was first discovered in the 1500s and what are we now like 600 years 700 years later yeah you know something that we've known that's incredible i'm also thinking, I mean, this is brilliant, Susanna, it's really getting me thinking about the potential implications across society, these scientific discoveries. But we talk a lot about muscle, right? And sarcopenia. And as we get older, we lose muscle mass. So arguably strength training is, it becomes more important as we get older. Yeah.

And I'm kind of feeling something similar with brown fat, whereby we have it as babies and you're saying after the age of 40, we're starting to see less and less of it. So arguably it's more important, potentially, I'm putting it to you, that we look after it above the age of 40. But I'm also thinking, I wonder if we had studied humans 200 years ago before all these modern comforts, you know, when people were more active, when they weren't living in these temperature-controlled environments.

I wonder back then, would brown fat have been lower after the age of 40? You know, is this a modern problem? It's a modern problem, definitely. I'm pretty sure it is because if you go back, we didn't see people at age 40 and above being obese like today. We didn't see that. So it's definitely from the 80s or something like that. We see obesity and lifestyle diseases increasing a lot. And we also see that exactly around the

same age, we see that people have less brown fat or it's getting inactivated in a way. So what I actually think is that if we use the cold as prevention also, you can keep your brown fat alive. If you keep activating it, it will be more efficient. It will also know it's like any other thing in our body. If we use it, then it's useful and then the body keeps it. If you don't use your muscles, they will also get smaller, right? So if you use your brown fat and you exercise it with always changing the temperature, then you will also tell your body, well, I actually need this. I need to increase my metabolism. I need to get cold. I need you to adjust my temperature so I won't die from hypothermia. And if you keep your organ alive like that,

you also get healthier. So that is actually what just practical what you're doing when you're going into the cold. You are telling your brown fat, I need you and I need you to be very efficient. So please increase more mitochondria

and please disband. It's like across society, we've traded in our brown fats for white fats. Yes, we have. Yeah. You know, another way of looking at it, it's really quite remarkable. Look, we mentioned the potential benefits for obesity and type 2 diabetes. And brown fat is one of the key mechanisms there for us to think about. We mentioned resilience and how deliberately doing something uncomfortable is going to make it

easy for you to cope with that stress, tolerate the cold, and that's going to transfer to other areas of your life. That's interesting. Let's go about the immune system. A lot of people are always looking, particularly at this time of year, how can we look after our immune system? There's a beautiful section in the book on this. You talk about lots of different studies. I wonder if you could start off with the cold shower one, because cold showers are probably one of the most achievable things for people across the world, right? They can probably get into a cold shower. They don't have to go anywhere, join a club somewhere all that kind of stuff so but that was a pretty powerful study i thought yeah i think so too it's a randomized control trial which was done in um in amsterdam i think it's in holland in the netherlands but

the study is about um cold showers versus hot showers you can say so. So all the participants in this study, they were divided into different groups. We don't need to go into the nitty gritty stuff about that. But the thing was that they wanted to see what happens if you end your hot shower on cold. What happens after 30 days if you do that? And if you do it for 30 seconds, 60 seconds seconds and 90 90 seconds which is not very long right okay so people are having a hot shower they have a hot shower and they did literally that at the end

they finish with cold but it's either 30 seconds cold 60 seconds cold or 90 seconds cold yeah okay that's not long that's not long but it's long if you don't like the cold. And it's also very stressful, right? So turning the, you can say, if you turn to the cold right away, it's very stressful. And then 30 seconds can be very long. But you can build this up just like the cold plunge or going into the sea. It's just about training this. But what they found, I found very fascinating actually, But what they found, I found very fascinating actually, was that they saw that ending on the cold shower for 30 seconds, 60 seconds or 90 seconds, it doesn't really matter apparently.

So 30 seconds isn't enough, but they saw that they have less sick days from work could be an outcome of maybe boosting your immune system. And that way you also feel better because of the chemicals in the brain. So it could also be that. It's the whole package of like going into the cold and getting this increase in all the brain chemicals, but also a boost in your immune system. So this boost has, in a way, kept them from being that sick that they need to stay home at least. So compared to the control group. So I find this very fascinating. So you don't have to go long. It's just, if you can build up to 30 seconds, then you will boost your immune system. That's a general point that I was going to make, whether we're talking about cold showers or cold plunge or winter swimming,

is it the law of diminishing returns? So do you get most of the benefit right at the start? Like with the cold shower, 30 seconds appears to be just as good as 60 or 90. And you see now a lot of ego, I think, being brought into the cold immersion world, which I want to touch on later because I think it's actually problematic where people are trying to out-compete each other. And I think just bringing it back to make it practical, it's the first bit, right, that gives most of the benefit. I think the reason why the first 30 seconds is just enough is actually that there's something called humesis. And humesis is the healthy stress.

Healthy stress is when you just shock your cells, right, from the cold shower or going into the plunge. And that is when the cell thinks, oh, this is dangerous. Oh, we need to do something to protect ourselves. then they build it builds itself stronger and that is kind of like phase two so the acute the shock and then it it makes itself stronger more robust in the second phase but there's also a third phase where you can exhaust the cells meaning that you overdid your stress you You overdid the stress, which means that it comes to being chronic, you can say. Even though you can say 90 seconds

in the shower is not that long, how can that be too much for the cells? Well, you need to think about temperature as something that is very, it is actually very stressful for the body. So you don't need to do it for a long time. You just need to awaken the cells and just you do it acutely. So the acute response is don't need to do it for a long time you just need to awaken the cells and just you do it acutely so the acute response is what we need and that is called the micro stress

micro stress is exactly what you you can say the sweet spot so you will have the healthy the healthy stress and then you don't need to go further you don't need to sit in a cold tub for 30 minutes because then you have exhausted your cells. And you will definitely flatten out the benefits. And we see that from sauna actually. Right. Yeah. So there is this sauna study. So you can say that temperature, either going cold or going hot, it's kind of like it's on a scale, right?

And in the middle you have the neutral temperature but if you go very hot or you go very cold it's it's the the body's going to respond to that in practically the same way because the the body will tell you well this is this you can have but this you but now it's getting too much too warm or too too cold for too long time and that's going to exhaust the cells so we see in these um finnish sauna cohort studies which i find very fascinating they are so fascinating they are i think they are up to now 27 28 years where they have followed these 2 000 to 3 000 uh sauna bathers and in Finland, they go into the sauna, but they also go into the cold.

Yeah, it could be a sea or it could also be rolling in the snow. Yeah, so different kinds of cold exposure. So they like go back and forth to the sauna. But what they see is that if people go into the sauna 19 to up to 29, 30 minutes, we see that they have all the good healthy benefits on the long term.

So this study is a cohort study. So they follow these people for many years and they see that they have all these healthy benefits of a better cardiovascular system and the lower risk of blood clots in the legs and also less stroke and so on. But they also see that if you go further than 30 minutes in the sauna, the benefits will flatten out or even actually increase the risk of all these outcomes that they have looked at.

So you can definitely look at this as well heat is also a stressor and that is cold also but cold is very much more potent than the heat is we have more cold receptors also on the skin yeah i read that you in your book you mentioned there's three to ten times more cold receptors on our skin than heat ones. But why do you think that is? Well, you can say you would die definitely quickly from being too cold. So from nature's side, this is very clever, right? It's really, really clever because we need the cold receptors to tell us immediately, now something is really, really wrong. You could get hypothermic within 15 minutes in cold water and you will die, actually. So need more cold receptors that is also why it's more potent so you cannot say well if i can stay in the sauna for 30 minutes or 19 minutes then i can also stay in a cold top

with water that is zero degrees for 19 minutes it's not the same because it is 10 times definitely more 10 times more potent yeah and the heat so there's a there's a relativity it's like um it's a relativity for athletes listening you can't you know you can't equate running a marathon 26.2 miles with cycling 26.2 miles no it's you know it's not the same it's not the same you'd have to cycle a lot more to have an equivalent effect. And I think it's a useful way to think about cold and heat. Maybe you need a bit more heat exposure to get some of those benefits, but you don't need much cold. I think it's a wider point here, Susanna, which I really want to just pause on for a minute because I think the research you've done is phenomenal, right? I think you are really bringing some solid scientific evidence

to something that many cultures have known for many years. But I think one of the things that puts people off is that they associate it with, you know, huge time commitments. I have to go in and tuck my head in and go cold for 10 minutes in an ice plunger with ice in it. And sure, for some people, they love that, right? And they go with their friends and they use it as a way to increase their exercise tolerance. I'm not criticizing that necessarily. But I think what you're saying here is really, really important. You don't need much. There are incredible benefits for your physical health,

for your mental resilience, for your weight, for your metabolism. You just need a little bit. And one thing I saw in the summer, there's this brilliant company in the UK called Brass Monkey. So in fact, they've loaned me a cold immersion. It arrived yesterday and I know later on you're going to talk me through. I'm a little bit nervous. So we're going to make a video of that and put it out there for people to watch if they want to. I'm a little nervous because I don't do it. And I think they've made it really easy for people because it's electronic and you can just turn the temperature to wherever you want it. Okay. Oh, fascinating. Yes, there's a cost implication to that for sure. For many people,

it'll be something that they can't afford or don't wish to invest in. I completely understand that. But there's a lot of high profile people in the UK who have got these brass monkeys. And what I saw in the summer is there was a bit of friendly banter between them saying, he's been in for seven minutes at this temperature, I'm going to go in for eight minutes now at this temperature. And I get it, it's a bit of friendly banter. But there is another side to that. The other side to that is that I think, A, that can be dangerous, potentially, if people are really trying to muscle through with their minds and stay longer and ignore the signs i think the other thing for me is like this feels like quite an

individual tolerance type piece where you know everyone's going to have a different tolerance for someone who's maybe never exposed themselves to cold in the past, like 30 seconds might be the equivalent of someone who's super trained doing four minutes. So I don't think you can compare. You cannot. And I think potentially it's problematic. Yeah. I think this is one of the things

that I would like also to get across. That is that going into a cold plunge or winter swimming, it should not be a competition. it is not a sport like that it is it is an individual thing that you do and you are tolerant to cold in very different ways and so people people are more tolerant than other people and this this is this is because of very different things because there's body composition, which will make it very easy for some or easier at least for some. And some are just actually more co-tolerant already because they maybe work outside. So outside workers have more co-tolerance than people sitting in front of the computers all the time, all day and sitting in an office.

all day and sitting in an office. But there's also that people should recognize that some people just have a more sensitive central nervous system than other people have. So for example, if you suffer from anxiety or something like that, then you have a more sensitive nervous system, right? But that should not only be the only reason. I'm just saying that people are different and this should be done in a very individual way. So you cannot compete. And competing in this would definitely just trespass the, you can say, the threshold for when your cells are getting too stressed, you can say. But it's also, it's a a different thing if you want to sit in a cold tub for a long time that is not about the benefits the healthy benefits then then it's about the mind control i think so if you go above two three four minutes in the in the cold the top or in winter swimming or whatever you do your cold exposure then it's about something else, I think.

Then it's about getting through something, getting through the stress and try to see how long can you go. And I don't recommend that because you can do that with other things, but I don't think the cold should be there because then there are the downsides of that. And risks, real risks. Yeah, exactly. And people dunk the head all the time. And I'm like, well, you don't really need to do that. Yeah, we'll get to those practical

things. I think that's really interesting. But you can get yourself into trouble here. If you stay in really cold water for too long and stop paying attention to signals, you know, you can presumably get frostbite and actually real damage as well. I'm not saying that to put people off. I think we're just trying to emphasize the point. Don't let your ego get involved. Don't start competing with other people. Maybe that's more of a problem with men than women. I don't know. I think so. Yeah. Yeah. Yeah. I see that. I see that. Do you see that? Yeah, I see that. Definitely. Women do this for other reasons. And I think it's very funny because I find wherever I go, I just went to the Innovation Roundtable Summit for corporates in Copenhagen. Amazing.

And more women have signed up to go and take the cold plunge with me or not with me as a guided thing, right? But they seem to be a little bit, I don't know if women are just more brave in this sense, but they kind of like go to the cold for other reasons than men. I think they go because of the experience, but also of the health benefits and of the way they feel afterwards. Because afterwards you get this mental balance and better mood.

And I think for many women also during menopause, and I think this is a way to like get this calmness in your body. But for men, they are driven by something else, I think, often competition. But this is also just nature, right? I think it's good. often competition but this is also just nature right i think it's good but i think it's what i want to say is that i want to emphasize why is the cold healthy for us but i also want to emphasize that that there's like there is also a threshold there's like we need to learn how much is good for us so not just right right now i think it's a jungle everybody's just oh doing everything and just staying there for 30 minutes.

And this is potentially very dangerous because they get hypothermic. And one of the things we know this from is something called the after drop. And that is your core temperature decreasing after you have been in the cold. So it's not to put people off or anything this but it's just to tell that doing something extremely like staying in the cold plunge for a very very long time you need to know that your core temperature would decrease after you go out of the cold because when you go out your your your vessel will will dilate again and Your blood vessels on the surface. Yeah, exactly, your blood vessels.

And the warm blood in your core will go out through your muscles and tissue that is very cold, and that will go back to your core again, of course. And then the temperature receptors will pick that up and send a signal to the brain, wow, now it's getting even colder. And that is because the body is, of course, trying to heat itself up, but it's getting a little bit colder. Could that be then helpful for people in the evening? Because we know one of the key signals to fall into a deep, relaxing sleep is core temperature dropping. So I'm just wondering if there is this after effect, could there be some potential benefits in doing it in the later parts of the day where you're sort of trying to assist that temperature drop?

Well, it's, yeah, so there are other things going on as well. When you go into the cold, you will have a release of, you will activate your stress, your stress system, right? And you don't want to get too stressed before you go to bed. system right and you don't want to get too stressed before you go to bed um but on the other hand as you said we get this decrease in in cold temperature and that is actually we can see that also in in we have seen that in in my studies as well that that our core temperature decreases and that is also what's what makes us sleep and pushes us into the sleep but the stress that you experience from the cold plunge will probably also keep you a little bit awake so but the funny thing is that when I started winter swimming I got very tired afterwards because I couldn't heat myself up as good as

I can now of course because now I am already adapted to the cold. So I don't shiver as much as I used to, but I got really sleepy afterwards. And I think that is actually because my cold temperature went down. And I must say that despite that I just said that maybe a cold plunge before going to bed or a few hours before is maybe not a great idea from a theoretical level, you can say.

But on the other hand, when I have done it, I don't feel that I am alert or anything. I don't feel it afterwards. I feel the mental balance afterwards because we also activate the parasympathetic nervous system, which is our relaxing part of our nervous system. So if we can stay in the cold water enough time to get over the cold shock then we get into this relaxed

mood you can say relaxed mode and i think that when i do that i could go home and sleep yeah i think for me that speaks to that the individual nature of all of us yeah exactly so for me, that speaks to the individual nature of all of us. So it probably depends what's going on in your life, right? So, you know, if you're someone with a huge amount of stress in your life that you're struggling to manage and cope with, well, maybe the cold at a particular part of the day is going to have a different impact compared to someone who's got, you know, maybe minimal stress in their life. And I imagine some people will do a cold plunge in the evening and can't sleep, whereas others, it'll probably be the best thing they can do. What defines cold? Like when we say cold water, is there a temperature

at which we, you know, it's officially now cold water? I don't know if stuff I say is anything official or anything, but I kind of like, when I wrote my book, when I started like researching got hypothermic and maybe even ending up being an accident or some people actually dying. Where can we see that the temperature was actually driving that? was actually driving that. And what I found was that 15 degrees Celsius and below, you could get hypothermic from that if you stayed in the water. 15 degrees. Yeah, 15 degrees Celsius. So the water temperature 15 degrees Celsius. And below, yeah.

But it's all relative, I think. So if you want to activate your brown fat, for example, you can definitely do that by just going into water that is just a little bit colder than your skin. So as soon as you go into something environmentally that is just a bit colder than yourself, then you get an activation in different degrees, of course. So if you have 19 degrees in a room, you will activate your brown fat because that is colder than you're used to, but it's also colder than your skin. So you will have an activation. So it's all relative, I think. You should think about it that way.

So cold water at 15 degrees will activate anybody's stress response. So I think that is, and also this is based on accidents from from also drowning accidents so 15 degrees and below you can say that is definitely cold water and i guess that speaks to the point we're sort of covering at the moment which is it doesn't need to be ice cold water with visible ice right because we often see that online people are in ice and again if you're trained for that yeah you want to do that hey cool but to make it really accessible to people you don't have to do that no yeah that's really interesting i have actually um i have looked into so um what i've been doing the last eight years is studying this of course but also the the relative difference of temperature and what is the impact on our body.

So what I did was actually I've made these different programs and made a course so people can go in and you can say, follow this and have a safe way to get started. That is one thing. But also you can say a course where you will, that is individualized saying that they follow these principles and in that way they will get safely through uh starting out as as cold plunger or winter swim or what you want to be yeah because that is what i feel that people ask me all the time so how do i get started and i can give them some tips how to get started but eventually people write me oh i i i kind of lost track because yeah i i couldn't find the motivation.

I couldn't find out what to do next. And I see people do this with ice and do I need to do that as well? But I think that people should think about the cold as something that is very relative. You don't need the ice, as you said. It's something that already happens as soon as your body temperature is just decreased just a little bit. So you can build it up and you can go to the ice eventually, but you don't need to start there. Yeah, that's super empowering. Look, I think your book's got loads of practical guidance as well. It's got all the scientific

studies. It's got some beautiful photos and illustrations. I think it's great that it's really going to shine a light on just how many different organs in the body are positively affected by this. I think an online course is great as well. We'll definitely put a link to that in our show notes so people can sign up and find it and use it to help them. I know some of those principles you're going to walk me through after we've recorded today in this cold plunge. And it's a pretty cold day already today. So in fact, that's a good point. When you're going in, let's say winter swimming, or let's say a cold plunge in your garden or at the gym, for example, how much does the air temperature versus the water temperature play a role? So in the summer,

for example, when people are super hot and they're like, yeah, I'm going to go and do some cold plunge or have a cold shower. It feels relatively easier, I'm guessing, on hot summer days than on this cool autumnal winter day here at the moment outside. You know, do you know much about that? Is there, presumably there's a difference in our perception of cold depending on the air temperature? Yeah. Before we get back to this week's episode, I just wanted to let you know that I am doing my very first national UK

theatre tour. I am planning a really special evening where I share how you can break free from the habits that are holding you back and make meaningful changes in your life that truly last. It is called the Thrive Tour. Be the architect of your health and happiness. So many people tell me that health feels really complicated, but it really doesn't need to be. In my live event, I'm going to simplify health, and together we're going to learn the skill of happiness, the secrets to optimal health, how to break free from the habits that are holding you back in your life, and I'm going to teach you how to make changes that actually last.

and I'm going to teach you how to make changes that actually last. Sound good? All you have to do is go to drchatterjee.com forward slash tour and I can't wait to see you there. This episode is also brought to you by the Three Question Journal, the journal that I designed and created in partnership with Intelligent Change. Now, journaling is something that I've been recommending to my patients for years. It can help improve sleep, lead to better decision making and reduce symptoms of anxiety and depression. It's also been shown to decrease emotional stress, make it easier to turn new behaviours into long-term habits and improve our relationships. There are of course many different

ways to journal and as with most things it's important that you find the method that works best for you. One method that you may want to consider is the one that I outline in the three question journal. In it you will find a really simple and structured way of answering the three most impactful questions I believe that we can all ask ourselves every morning and every evening. Answering these questions will take you less than five minutes, but the practice of answering them regularly will be transformative. Since the journal was published in January, I have received hundreds of messages from people telling me how much this has helped them and how much more in control of their lives they now feel. Now, if you already have a journal or

you don't actually want to buy a journal, that is completely fine. I go through in detail all of the questions within the three-question journal completely free on episode 413 of this podcast. But if you are keen to check it out, all you have to do is go to drchatterjee.com forward slash journal or click on the link in your podcast app. Depending on the air temperature, depending on what temperature your skin is already, also what cold temperature do you have. If you are on the beach on a summer day, you will probably be very warm. But the relative difference of your skin temperature and then going into the water, I don't know about other places, but in Denmark, the water never gets really warm.

I don't know about other places, but in Denmark, the water never gets really warm. The sea is like, it could be up to maybe 22 degrees or something like that in the summer. And if your skin is then burning hot from staying on the beach, you can actually go in and actually have a little bit of a cold shock. Okay. In Denmark, at least. But so the relative difference is very important here. But as soon as you go into water that is 22 degrees, it will only take a few seconds for you to get adapted to that temperature, of course.

But you can use cold and heat all year around. And I think this is something, and heat all year around. And I think this is something, I think we should use this in our daily health praxis. I think we should think about temperature change as something that is super healthy and natural and cheap and even free for all, almost all, that we can use this in our daily life

to add on to our training, to add on everything else that we can use this in our daily life to to add on to our training to add on everything else that we do and it's so easy and it's so fast it's not very time consumable i think to do this it is very very easy quick and you can you can do it all year round also in the summer so i don't think that people should think about it only as winter swimming. I know my book is called Winter Swimming, but that is because we name it that way. But actually, all year round, we can do this. Also, if you have your plunge, for example, you can use this in the summer and standing in the sun for just a bit and going into the cold water. I mean, you would definitely have more of a shock at a higher temperature, water temperature degrees in the summer, because the relative difference of your skin temperature and the water is going to be the outcome of that.

So basically what you're saying is that it's going to be easier for me today because it's already cold. So I'm feeling even more pressure now before we do this. Well, I've got this, as I say, I've got, you know, Brass Monkey have loaned me this unit for, I hope, a few weeks. So I'm looking forward to experimenting with it. Obviously, we've covered my wife and let's see if I can get her into it over the next few weeks um my kids are similar ages to yours 12 and 9 any kind of tips and advice as to whether I should be doing this with them anything to look out for I would very much like to I'd like to model certain behaviors to my kids all the time you know they're going to see daddy very shortly going in every morning, probably.

And I suspect they may want to have a go. So what do you think to that? Safe to do so? Any guidance you'd give me for that? Yeah, I think it's safe to do so because you're there. And always think about everything, cold plunging, winter swimming as something social. I don't, I don't tell, I always tell people to always bring a swim buddy. It could be your, it could be a wife. That could be something you'll tell, well, I need to have someone with me all the time. But with

your kids, of course, you need to be be there and one thing that i looked into i think i also write about it in the book but um more and more people bring their kids um to winter swimming and plunging stuff and i think it's a it's a good idea based on what i found um but there is very it's very important to think about the children as they're very much smaller, right? They have a bigger surface area relative to their mass, meaning that if they go into cold water, they will be able to keep their cold temperature just as long as an adult. I have found studies showing that,

but they will definitely have a faster decrease in cold temperature right after, meaning because they have so much surface and that much less mass to keep the temperature up. So that means that what I advise people to do is go, if they bring their children, that they just do a quick dip. A quick dip in the ocean because they will have the benefits of that. They will, you can say, healthy stress their cells and they will get an increase

in all the good chemicals in the brain and get this mental balance, the state and calmness afterwards, just like adults would. But if they stay as long as adults, this is really risky, I think. They will get hypothermic. So in practical terms,

and I know every child is different and depending on which country you live and the air temperature and the temperature of the water, it's all going to be a bit different, but something like 30 seconds seems reasonable. I wouldn't put a number on it, I think. I think it's very important that people, also kids, are taught before they go in how to listen to their own body. And this is something that nobody is actually very good at today because we have for many years in Western medicine been taught that if there is something wrong, we will get a pill or something. We don't know how to listen to our own body.

We don't know how to concentrate or focus on anything. How can I feel a signal from my body? Well, if you co-plunge, you will at some point, and that is what I think you should tell your kids, at some point you will feel now this is too much. You'll get a little bit of a chill.

You can feel maybe down the spine or something on the arms. I also hear that. Then you know, okay, this is enough. And then you get up. It would take about a minute to get over the cold shock. So as soon as you go in, or maybe actually standing in the wind for just a bit before you go in, you will activate the cold shock

response. And to get, you can say, to the calmness and full activation of your parasympathetic nervous system and getting this calm state of mind, you will need to get past that. But I think that adults should do that. And I think that if you train your kids and they try this multiple times, they can also get there. But I wouldn't say that they should stay in there for multiple minutes, just like we have so much research on the physiology of adults, but we don't have that on kids. Yeah, I mean, there's so much there that I love, Susanna, that speaks to my heart. One of the main reasons I would like to take my kids in is to teach them resilience, to teach them that they can cope with hard things, to teach them about the power of their breath, and if they can control their breath, slow it down, they can change their experience of stress, their experience of cold,

frankly, their experience of life. I always try and do things like this with my kids, because I kind of feel across society, you know, we're so keen on safety now. And I get it. I understand it. Okay. I'm not trying to say we should expose everyone to everything and people get sick and people get hurt. But I think we have, I think we've gone too far. Everything's now trying to be so safe. No element of risk. I think it's sanitizing our lives. And I think we all, it speaks to this sort of idea of comfort, doesn't it? We need to expose ourselves to discomfort. We need to do things sometimes where there is an element of risk, but we can do it in a controlled way. I'm

not talking about throwing the kids in the ocean when they can't swim. It's like, no, with me observing in some cold water, what happens when they do it. And I suspect, and I don't know yet because I've not done it with them, but even if they struggle at first and within a few days they're like, oh, I can now do 30 seconds. I couldn't get in the first day. Exactly. That feeling of self-worth and inner confidence is worth it's priceless yeah there's nothing better than that i think that's an important message you mentioned cold shock and we can even get it just standing in cold winds yeah and there's a few terms i i wonder if you could explain you you've mentioned the after drop so how after you've exposed yourself to cold, you know, your temperature can keep dropping afterwards.

There's also this term called cold shock response and diving response. I wonder if you could explain those terms, please. Yeah, so the cold shock response is when you go into the cold water, as soon as you step in, you will activate the cold receptors in your skin. And that will send a signal to the brain saying, well, this is very, very cold. So norepinephrine will be released and that will contract your blood vessels. So you won't have all the blood in your skin. As soon as you get more into the water and you submerge up to the neck, you can do that. You will also activate the diving response and that is actually activating your parasympathetic nervous system

so you have like an activation of both the stress response in your body but also the calmness you can say at the same time so the cold shock on any part of your skin yeah activates the sympathetic nervous system which is the stress the stress arm of our nervous system yeah exactly and if you get it what up to your neck so what covering your shoulders or is that are there specific receptors that we need to cover in cold for this diving response to be activated i don't know if you can get it from only submerging your legs, but I don't know that. But I think that if you go up to your neck, up to your shoulders, you would definitely have that activation. And that's one of the fascinating things for me about cold. From studying the research and reading your book, it's this idea that cold activates the sympathetic arm of our nervous

system and the parasympathetic part of our nervous system and I to my knowledge I'm not sure of anything else I've come across that does both at the same time this is I think it's fascinating because that is exactly why when people ask me should I do should I do cold showers? Is that just as good as going into a cold, doing a cold dip? And I think exactly that with the activation of both part of your central nervous system is where you benefit more

from doing the cold dip. So when you have that activation of both sides, you also have a conflict, of course, in the body. And that is where you can say, well, it's also a bit of a stressor for the heart, of course, in the body. And that is where you can say, well, it's also a bit of a stressor for the heart, of course, because you have the fight and flight system going up, making your heart rate going up, but also the parasympathetic nervous system trying to get

the heart rate down. And that will make the little conflict in your body. Yeah, but I guess this whole thing, this whole idea of a controlled form of stress is talking about you know exercising and working out your nervous system yeah exactly you know and they're training your brain to get to get more comfortable in a stressful situation yeah yeah you're training your body you're training your mind at the same time and it's it's kind i think it's it's kind of amazing. And the more I research in this, the more I dug into it, the more I found out that this is not only, this is of course not only from a physiology level,

a good thing, but it's also, as you said before, it's like pushing your confidence in yourself. And we see that a lot. We see that all the time. And I was like, when I went out to watch winter swimmers in the beginning, when I started my research, I was not a winter swimmer at the beginning. I was like, what is going on? When they jump into the water, they are

a bit scared, some of them. And then when they come up, they like dunk themselves on the chest, like, and saying like noises like Tarsen. They looked like superheroes. They looked so confident. And I was like, that I don't understand, but I need to find out. But it took me actually a while to figure out what was actually going on. The confidence that people get from this short time, you can say it's a success every time you go. And I've been winter swimming for years now, three years. But I feel the success every time I go. So it's kind of also a way to boost your self-worth, but it's also your confidence. And when I can get across that stressful situation every time I go, I know that I can also do that in all other situations. for sure for sure you can you can tell that to your kids because when you push yourself in this

way you can you can take this way of conquering a stressful situation in other other life situations and knowing that i could get through this then i can also get through something else yeah speaking about mood and depression and anxiety, things which are rampant and increasing at the moment, there's many ways to look at those conditions. And it's becoming clear that there's so many elements of our modern lives that are contributing. And if we can change various aspects of our lifestyle,

we can get improvements. And, you know, I'm thinking about this idea of a window of tolerance, you know, being very narrow now for many of the reasons we've already mentioned. And if I think about a lot of the patients who I've seen over the past couple of decades with depression. A lot of the time they talk about, you know, apathy, indifference, this very narrow experience of life. And I have this very powerful image in my mind at the moment about, you know, things like cold or even heat, just almost like shocking them out of this kind of very narrow experience of life and broadening it and giving much more perspective. Yeah, exactly. Does that sort of fit with your understanding?

Yeah, exactly. I think that exactly that was what I found out when I was researching to my studies, but also to my book. I didn't know that I was going to write this book at that time. I was just very keen on understanding what was actually going on in the body. And I was very focused on the body because I was studying the brown fat, which is a physical organ. But I was also very puzzled by the whole thing because then i went to the mind and i needed to read all what is happening in the in in in our brain when we go into the cold also when what happens when you go into to the heat in the sauna but what i couldn't connect was that feeling when people get into the cold and this perspective that I could hear people talk about

and they talked about it in the same way and I know they didn't talk together about telling me this so everybody talked about it in the same terms of like feeling in this kind of like zen mood afterwards and being in mental balance but also like, people told me that it's very difficult to understand completely what it actually does. So, but it definitely gives some kind of perspective in life. And this perspective comes from getting out of your body, out of your mind a bit, being shocked a bit, but in a controlled way. You know, thinking about mood issues, I'm not sure there's anything better than going in cold to immediately get you out of your head. You literally, you can't be in your head. You can't think about your anxieties and your worries

and your email inbox and your shopping list. You can't do it in the cold because straight away it brings you into your body doesn't it is exactly you cannot because you go into survival mode right so as soon as you go into the water the the sympathetic the fight and flight system will start and in that situation if you think about us back when we were hunters, for example, we could not think about, oh, what is actually going on back home or we are sitting in the water and thinking about what to shop next tomorrow or what I need to buy. You cannot think about anything else. You are in the moment.

Whether you want to or not, the code would get you there immediately. You cannot decide this. You would definitely get there immediately. You cannot decide this. You would definitely get there immediately. So that is why it's good when you asked me before, is this something we should tell anybody, everybody? Should everybody do this? And I think, yes, we are in a society right now where we are overwhelmed. We are overwhelmed in a way where we can see statistics of depression, anxiety, and stress curves

going right up. You can go to the World Health Organization and see these statistics, and it's actually a bit scary, I think. And what are we doing? We are trying our best, I would say. We're trying our best to solve it in a way, making more medication. But we have so much medication also. We have so much and we are fighting to get more to help people.

But I think we are missing the point. The point is that we are just working ourselves into this more and more and more and forgetting where do we actually come from? Can we do something completely different and take ourselves back to something we know this will actually work? I love that. Where do we come from? That's kind of it in a nutshell, isn't it? This is who we are.

This is who we are. And there's a beautiful section on page 243 of your English version of your book. Let me just pull it up. Do you mind me reading it to you? No, no, please, please. These are your words, and I underline them, so I really love them. Nature with its simple but harsh presence

does not deceive, as opposed to the internet and social media and their endless guides and advice. Nature is sincere. It's neither for nor against us. I think that's so powerful, Susanna. The way you wrote that, I think is beautiful. And for me, it really speaks to this idea that try it, right? You know, sure, listen to what I've said or you've said, read your book,

right? But that information is going to do nothing, right? It's going to do nothing unless you actually do it. And the code will be your teacher. It will probably showcase all these things that they're hearing about in our conversation. It will teach them if they do it. And I feel like a lot of the time these days, Susanna, I don't know, again, I don't know what it's like in Denmark, but I feel these days, you know, there's so much information everywhere online and loads of great people online who are sharing information for sure. But I think sometimes we were consuming all this information. I think, yeah, that's great. we're consuming all this information.

I think, yeah, that's great. And we drop a heart or we drop a like on Instagram. And we think that we've done something, but all we've done is actually move our thumb. That's the truth. All we've done is move our thumb like half a millimeter forwards. And we think, yeah, you know, I'm doing something. We did nothing.

Whereas I'm just trying to bring it back to the cold. It will get you out of your head yeah it will shock your system it will bring you into your body exactly and it will remind us from where we've come yeah exactly one of one of the questions i often get is why why why actually why do this and do we need? That is also a question I get a lot. Why are we talking so much about this? Or why are you talking so much about this? Why should we do this?

And I think one of the reasons is definitely that there is a need. We also see that there is a lot of attention around this at the moment. And more people are doing it, which is great, I think. But there's also very much many people are asking these critical questions and I love that, keep them coming. I love it. That is what motivates me because I love questions. But it's like also at the same time, answering this must be because there is a need. Answering this must be because there is a need. A trend or a new, you can call it health revolution, doesn't start because of no reason.

It's because we need it. And we have looked everywhere, definitely in the medicine field. We have looked to solve depression and anxiety. And we have tried to keep people, you can say, not keep people healthy, but curing them from a disease. But what do we do to help people prevent a disease? We don't have a lot, right? And we don't have many places to go.

So we need to do something different. We need to change something because our stress, depression, epidemic is just rolling on. It is just increasing. So we need to change something. And I think this is definitely one way to do it. I think this could definitely be a reason. So this is your why. This is preventing lifestyle diseases.

This is preventing depression. This is preventing lifestyle diseases. This is preventing depression. This is preventing pain. This is really helping people from this one kind of exercise that you do, just going into the cold. You don't have to be good at it or good at anything, actually. This is just going in to the cold. It's something everybody can do. If you don't suffer from heart diseases or unregulated heart

high blood pressure i think that this is definitely something that we can we can tell people to do in a controlled way we've mentioned noradrenaline already one of these um chemicals in the body that gets released when we expose ourselves to colds. I think we should maybe just explain what noradrenaline is, what it helps with. But also one of the things I love about the colds and the research is that, yes, noradrenaline goes up, dopamine also goes up, and it's a sustained release, isn't it? It's not just for like 10 seconds. Some of the research I've seen, it's hours, right? Yeah. I think it's so fascinating when we look at noradrenaline. So noradrenaline is both a brain chemical, but it's also a hormone that is released from our adrenal glands. So you get it from two places in the body when you go into the cold.

I have found out that, I wanted to see where does it release first, but it's definitely from your brain that comes first because it needs to activate the brown fat as well, right? So you don't freeze. But it also comes from your adrenal glands. That has increased within minutes up to 250% above baseline. That is a lot.

And it's so rapid because it needs to save us, right? This is our fight and flight system. So we need the fast response. We cannot get that from the heat. We need to get that from the cold. So no adrenaline goes up 250% above baseline within a few minutes. If you can build that up, then you are good, I think. That is what you need.

But at the same time, you also get that increase in dopamine. And dopamine is something that is really, really good for our drive, our motivation, and for getting good habits as well. When you get this release of dopamine going into the cold i won't say that you will get addicted to the cold water but you will get a really really good feeling around going into the cold water because you get this happy good feeling good mood good drive good motivation and afterwards and this for hours, up to four hours afterwards. But if you compare the dopamine effect, the increase from going into the cold,

if you compare that with anything else, that could be, you also get that from cocaine, for example, or alcohol, nicotine, you also get this high increase when you do that. But the difference is You also get this high increase when you do that. But the difference is that you don't get the rapid crash afterwards. So if you do drugs, for example, you have a rapid crash afterwards. That is why people go out and want more and more and more often also. But if you go into the cold, you will have a natural increase in dopamine, which will only make you feel better, but for hours afterwards. And this motivation and drive and good mood, you will have that for the rest of the day.

Yeah. I mean, who doesn't want that? Let's say you're well, you're listening or watching this right now. Who doesn't want more noradrenaline, so more attention and focus, more dopamine, more of that feeling of reward and motivation and drive. We all want that in our lives. But if you're struggling, if you feel low, if you struggle to get out of bed in the morning, you feel indifferent, maybe you've been diagnosed with depression, whatever it might be, you kind of want those things even more, you know? And I guess just to really hammer home the point, what you've been saying continuously throughout this conversation is that it doesn't need to be long, right? So if that person is struggling at the moment with the cold weather, the dark,

low moods, I really, really from my heart would encourage them, maybe get in that shower, do 30 seconds cold, just get yourself the motivation to get in there and just see what happens. Do it day after day for, let's say three, four days and just observe what happens. Do you know what I mean?'s it's that simple but that it's very simple that effective as well it's so effective but also i want to say don't give up because if you if you go the first time you will probably not get all the benefits from the first time because you cannot stay long enough to get the high release of everything good going on in your body you have to get through the first three four five rounds i mean so you need also to keep to it and believe in it just stick

to it because it's like it's like starting up exercise and in in your in your training center right it will hurt the first five kilometers you run will definitely hurt more than when you do it five times right and you are you don't start with a marathon right you never do that so you don't start with 30 seconds in the shower you start by five seconds and then you build up to 10 15 and maybe you can do 30 at from the beginning but that's because people are different so just just believe in it and just keep pushing it because at some point you will get you so adapted to it it won't take long but it will definitely take a few times so that is why i'm saying no don't give try it first time and you're like oh that's not for me yeah that only hurt

yeah it hurts the first time running five kilometers after a long break also hurts yeah there's a wider point there for me and first first of all, thank you for making that point. It's really, really important. Now, of course, some people won't be able to control the temperature of the water. So let's say they're winter swimming, or let's say they're part of a local club and they go for cold dips. I know that's very popular in Scandinavia. I know it's growing in popularity in the UK. I know that's very popular in Scandinavia. I know it's growing in popularity in the UK. You can't control the temperature there. So you have to go into whatever temperature that is, right? But many people now, or I guess a few people are either using cold plunge at a gym or they're having things in their garden, but they're putting in ice and they're

actually trying to, in as cost-effective way as possible, replicate it at home. Now, first time you go in, of course, you're not habituated yet, so it feels difficult. Over time with regular practice, like with exercise, like with most things, we become more tolerant. And so let's say you go into 10 degree water, right? Cold water. Suddenly you're 15, right? So 10 degrees. First time, you find it really hard. You can manage 10 seconds. Let's say after a month of doing it regularly, you can now do it for four or five minutes and you're like, no problem, right? Should one stay there or is there a benefit to dropping the temperature? So going from 10 to nine, like let's say you're

lifting weights and you know, you're first of all struggling to lift that weight two times, you keep practicing, you could do it five times, you could do it 10 times. And then at some point, someone will say, well, instead of lifting that weight 10 times, why don't you go to a heavier weight and only lift it five times? It's going to have a different benefit in the body. Do we know yet? I know it's early days in all of this research. Do we know yet whether as you get habituated to a certain temperature, there are additional benefits from lowering that temperature?

So we know that if you keep changing or that is you can say if you look at physiology just if you keep changing the temperature you will keep pushing your central nervous system and you will keep pushing the activation of the chemicals in the brain so what i always say is that you should keep changing the temperature. You can also start with 10 degrees, as you just mentioned, and just try to get habituated to that for a while, but then you need to also change the weight. So the temperature could be the weight on your weight. So go down, you mean? Yeah, you can go down, but you can also go up a bit. So as soon as you're changing it a bit, then at some point you cannot get lower, right?

But then you also stay less in the cold water. So there is a dose response, you can say. So as the temperature gets colder, you stay, of course, not that long in the water. But if you keep changing it just like nature i always say if you went to swim in nature in the sea or a lake or whatever you have the perfect temperature regulator right there yeah it would change it for you the seasons will change it for you if you live at least in a country where you have the seasons. Yeah, exactly. But if you don't have that, then you can look a little bit to what temperature do we actually have here?

Do we go below zero? Maybe not all the time, right? So changing the temperature will challenge your cells and it will challenge your mind. And in that way, you will keep exercising your cold tolerance. You said you love questions. A question that has been popping up for me as we've been talking. And before I say, I appreciate that, you know, you live in Denmark and a lot of the research you're doing is in Denmark. We think about our evolutionary nature, where we've come from, and how that might impact our

tolerance to cold. It might impact our levels of brown fat. And then I think about myself, you know, my ancestors are from India. So, you know, a lot of my ancestors, I imagine, would have pretty warm temperatures for most of the year. Depending on where you are in India, it would never get mega cold. You're not going to get that sort of coldness in the winter that we're going to get in Europe, for example, or certainly in Northern Europe. Do you know yet, have you been asked yet, how different cultures, how different ethnicities affects levels of brown fat that we have and our ability to tolerate cold. So we know there is a difference in brown fat,

in how much brown fat that we have across the world. So we would definitely see that some people also living in the colder countries, they have a bit more brown fat. We also know that women have more brown fat than men. And I think it makes sense. So if you are in a country where you would need the brown fat, so it's just the environment telling us that, well, we need this. But from nature's side, if you live in India or you're from India, then you will maybe not need as much brown fat as one who lives in a colder country. Women, for example, we are smaller, we have less muscle mass, and we have a large body surface, of course. And that means that we get colder easily easier than men we get colder easier

than men and because of that we we probably that is probably why we have more brown fat than men has because you have the muscles who that can heat you up but for women we don't have that much muscle mass so we need more brown fat to heat us up. So it's always something about, I'll come back to it again, it's also about the request. If we request the body to heat itself up because we live in a cold environment, then you will also have more brown fat. But people from India or people from, you can say, warmer countries,

including myself, I'm half at least Sri Lankan and half Danish. Okay, fantastic. So I'm half at least Sri Lankan and half Danish. Okay, fantastic. So I know India and I know Sri Lanka and it's very, very hot. I know from myself, and this is just from my side, I can only tell from my own point of view, that if I compare with my friends in Denmark who are Danish, they adapted to the cold faster than I did. And I would say I'm a cold sissy.

And I think it's absolutely, I was a cold sissy. I was really. I didn't want to become a winter swimmer. I was definitely one of those saying, well, I studied this. Do I really have to become one myself? And it took me a while to get convinced that I had to. But what I wanted to say is that I went through the cold and I keep pushing it.

So I didn't give up. Luckily, I didn't. But it took me a longer time to get cold adapted than my friends. It's so interesting. First of all, I love the fact that you, Dr. Susanna Soberg, arguably one of the world's leading researchers in this area is calling herself a cold water sissy or a cold sissy. I think that's brilliant. But I think, I think it's a, I think that's a really important point that it speaks to that competition and ego piece from before that everyone's going to be

different. Your ethnicity is going to play a role. Your ethnicity is going to play a role. Your sex is going to play a role. I think many people, Susanna, will relate to what you said about women and men experiencing cold differently. I mean, it is such a common complaint that in a bedroom, the women want it warmer and the men want it cooler. I mean, this is a huge source of conflict, I would say, in certain households.

What temperature do you set the bedroom at? So I think that's really, really interesting. It also makes me think of my perception. I once went about, I guess, two or three years ago. We were staying with our friends in Bristol. And my friend Jodie is a member of a, she goes cold plunging in the winter. She drives about, I think, 30 minutes out of Bristol to meet her friends. And we were there, I think, at New Year.

And one morning she said, do you want to come? And I thought, you know, I'm game for anything. So I went. Oh, wow. This is years ago. I can't actually quite remember everything about it, but I remember there was more women there than men, number one. Number two, a lot of people had hats on and mittens on. It was freezing cold. And my perception of that and other experiences is that women, I feel, tend to tolerate the cold. It almost speaks to the opposite of what you're saying here about cold tolerance.

I kind of find a lot of the time women can deal with the cold better than guys. And I think, is that just because as I'm coming to realize as I get older that women, I think, can tolerate pain and discomfort a lot more than men can? I don't know. Help me understand that. I think you just answered it. I think that might be it. I think women are built to tolerate stress and pain. Childbirth.

Childbirth, exactly. So I think that's one thing and you i don't know if you call it the same thing here in in the uk but in denmark we call it the man flu the man flu when when men have the flu it's just a little bit of pain and they're like oh my god and i mean i think half my audience is gonna love that half of them might them might not share the same perspective, but that's okay. Oh, no. Yeah. But I think that there is a bit of, I think there is a difference here in how we, our perception of pain and perception of stress even, actually, because it's so linked, the pain, the stress.

It's so linked. You can feel, you feel more pain when you're stressed, right? And you actually also feel, you feel more pain when you're stressed, right? And you actually also feel more cold when you're stressed. That's also because of your veins are contracting and you feel it more. But women are very good at pushing the stress boundaries, I think, because they also build for it, I think. But this is only something that we can speculate. We don't have any real evidence for this. So regarding the different cultures then, it's fair to say that

as things stand, it's legitimate to think that people from different parts of the world will have different baselines level of brown fats. But we have no reason to believe at the moment that there's a limit for people like even if you your ancestors from a hot country even if you've grown up in a hot country you can increase the amount of brown fat you have if you start exposing yourselves to cold exactly and it's really fascinating for me how this research you know i wonder do have you have you any knowledge of research being done in hot countries you know do they even do this in hot countries in a way that they do in in europe um

in in kind of like cold plunging and no i don't i don't i don't know actually because sometimes we don't know what exactly is going on for studies in other countries. We often, we can go and look up ongoing studies if they are put into a certain database and we can look that up. But often we only know it when it's published. So it could be that right now, some more studies are actually going on also in hotter countries.

But we know that there's a difference in co-receptors in the skin across the world. There was also a difference in the brown fat amount across different countries, hot, cold countries and regions, you can also say. But I think no matter what, I think no matter what, that you will benefit from going into the cold. It's just the amount of time that you are in and what temperature. You need to do that on an individualized plan. One of the things that actually I wanted to do when I kind of designed my study,

because as I told you, I used to be a cold sissy. And I was like, the main topic, the main thing for my research in my PhD was to find out if i can activate the brown fat in a way where we can actually use this is make some kind of way that we can increase our amount of brown fat or the efficiency and i wanted to do that because i wanted to do something applied research um something that is useful there's it's been driving me always doing something that we can we can use for something and it and it's not supposed to always doing something that we can use for something

and it's not supposed to be a pill that was one of the things I wanted to do something that prevents also diseases because we have a lot of like curing stuff curing diseases and we need it and we need it it's not critical against that

we just don't have enough knowledge about our physiology and where to address it in preventing our diseases, our lifestyle diseases. So I wanted to do something like that. So what I did was to think about how can we activate the brown fat in a way that is accessible for most people. And I found research showing that going into a cold room and sleeping for a month will increase your amount of brown fat and increase your insulin sensitivity but sleeping in a in a room that is hot again the next month then decreased it so that kind of like confirmed that the cold is activating the brown fat and increasing and it gets more efficient in

that way but that is not very that is not something everybody would like to do sleeping at 19 degrees but also there were studies showing that wearing a cooling vest for 10 days um eight hours will also increase your insulin sensitivity and you will have more brown fat. So hold on, you're going about your everyday life, you've just got a cooling vest on. Yeah, and you can buy these. But I was like, well, I like the proof of concept here. I love it, because that proved that if you expose yourself to cold, but this was quite a long time, and wearing a cooling vest, then you will increase your brown fat. And I was like, well, that's very cool.

But, I mean, who wants to wear a cooling vest all the time? I don't know. I mean, that was just not the study that I was going to use. So I was like, what can we else do? So that is why we came up with, what about the cold in winter swimming? Because we live in Denmark, so many people winter swim.

You mentioned a bit of research in your book where I think in Denmark, when people were asked about a list of things that they love to do, winter swimming came up third. Yeah. At that time, when I started my research and when I did that questionnaire, I did a questionnaire when I was writing my book, I had talked a lot in also the media about what am I doing

because I was doing something completely different. I was studying winter swimmers and then people were like, we are studying winter swimmers. Why? That is just something that some people do, but it's kind of like a little bit, yeah, niche, right? But they were very interested. So I did this research around it. And so many people actually answered that what they love to do is winter swim and eat chocolate. So it's like on that level in Denmark. And I loved it because that was like, okay, I got at least support from people. I love that. They love it as much loved it because that was like, okay, I got at least support from people.

I love that. They love it as much as they love eating chocolate. I mean, again, for that person who's skeptical, like give this a go. You know, when did you start researching? About eight years ago. Yeah. Right.

So I'm guessing back then it wasn't cool. It wasn't fashionable. It wasn't like taking over all the wellness Instagram accounts. Not at all. Right. What was it like for you when Professor Andrew Huberman talked about your research, called it the So Big Principle, right, on the biggest show podcast on the planet,

the Joe Rogan podcast, Joe Rogan Experience. Like what happened? What was it? You know, how did you find out? What was it like for you? What emotions came up? Well, he told me in person that he was going to do that. He was going to talk about my research on the Joe Rogan Experience. He told me right before. And he said that, I know that you're ready. You can talk about this. You are ready. And I was like, am I ready? For what? And I was quite surprised.

And then when he went on, I was like, man, he's doing it. He's talking about this and promoting it. He's promoting the cold. And he's also promoting my research. And I'm just so grateful. I mean, so grateful that I'm doing something that actually makes sense and that is useful for people. That is what I wanted to do back then

when I started my research. I really wanted to do something that was useful, something that you can go out and give advice around, right? So when Huberman contacted me when my research paper came out, I was like, yeah, okay, hi. Yeah, and you would like to talk to me about this research? I was like, yeah, okay, we can talk about that.

But I had no idea that he was so much a fan of the cold. I didn't know that. And I also didn't know that a lot of his followers were a fan of the cold. And I think that kind of like yeah they're kind of like i i was so honored i was i was so honored i mean this has been so important to me i love that it was so important to me i'm so happy and grateful that i am doing this and i'm i'm so grateful that so many people are supporting and that huberman is supporting and he has this great podcast i mean yeah it's insane it has just been skyrocketing the last year i think it's yeah he's

he's great he's such a nice guy and it's it's just so wonderful that important research like yours which has got so many implications for individual health and societal health is being elevated by people with huge followings you know and to have it spoken about by Andrew on Joe Rogan I imagine must have been quite a special moment it was really special yeah oh fantastic I'm so grateful to both both of them really it's really it's really made an impact on my life definitely changed everything oh fantastic one thing i wanted to talk about is culture yeah and we just mentioned that that bit of research you conducted in denmark where winter swimming is a thing that you know a lot of people enjoy and want to do you also touched on sauna in your book. There's a whole chapter on sauna.

And what's really interesting to me is that certainly here in the UK, we associate sauna and cold with Scandinavia. If I remember, this is how many years ago now, I remember when I used to work in Timperley, which is a little village in the Northwest of England. I used to go to the gym on the way to work in the morning. This is pre-kids. I think I went at about half six when it opened and I'd do about half an hour in the gym and then I'd finish off in the pool. And there would always be this, there was this Danish guy who I got to know. I can't remember his name now, but he would always, he was there for like an hour, literally going sauna, cold brunch, sauna, cold brunch. I remember chatting to him. This is years ago, right? So I knew nothing about the research. I said, Hey, what's going on? He goes, no, no, it's great. It's really good for

my circulation. So again, an anecdotal kind of, you know, just a comment. And I thought, yeah, sounds good. I'm going to try it. So I, you know, I tried it for now and again or a few weeks, whatever. I don't actually remember. But this whole cultural phenomenon, like, are you finding that certain cultures are more willing to accept the information and act on it than others? I don't know. You know, do you feel in Denmark,

is this message landing in a particular way compared to, let's say, the UK? Have you got any experience with that? Yeah, so it seems like in Denmark, because we have this culture around, it's also cold in the UK, so we have about the same, you can say, temperature-wise air and water. But in Denmark, there is definitely a culture around winter swimming. And we don't really have a sauna culture in Denmark. We don't really have that,

but we have like borrowed stuff from Finland and we have borrowed a bit from Germany where they do the sauna goose, which is like putting water over the stones and then swinging the towels around and then putting essential oils on and stuff like that.

And also maybe sometimes listen to music inside the sauna. So there's different cultures coming in. And in Denmark, we have been practicing this for a while now, maybe 10 years or something like that. But it's mostly cold in Denmark, isn't it? It's mostly cold, yes, exactly. But the sauna culture is very new in Denmark as well. But it's starting to pop up more and more.

And we like, apparently, we are a culture where we like going back and forth and so doing the contrast therapy for blood circulation. We adapted that quite easily, I would say. We take that in as a culture because we are, yeah, I don't know, Scandinavia close to Finland and Germany where they already are doing this. So we adapted that. So I think when I did my study, I wanted to, one, I wanted to find out an easy protocol with how low dose can we get health benefits from the cold. That was one thing.

And also I wanted to study a method which was already very much used in Denmark. And that is going into the sauna and going into the cold. So my study results are based on the contrast of activating your cold response, but also activating your heat response. Yeah. You know, having spent quite a bit of time in Scandinavia over the past few years, when my books have been released there. You know, Sweden, Norway, Denmark even. What strikes me is that, you know, the culture tends to be a lot more equal than we often see, let's say here in the UK or certainly in America, I would say. And there's a lot of research on Denmark and happiness.

Oh, yeah. You know, I read about the culture there and how, you know, in certain organizations, culturally, the CEO will only earn a certain percentage above what the lowest paid worker is going to get. So it's not going to be like huge differences where the lowest paid in the company is on this amount and the CEO is on a different amount. I've heard that a lot of the social activities,

whether it's golf or whatever, you can have like a CEO of a company playing alongside someone who cleans toilets in an office building. It's always fascinated me. And of course, that must be a contributory factor to happiness and general well-being. But then if I look at the cold through that lens, and I think about culture, what's really interesting for me is that, you know, going in the cold in clubs, in community with other people, like you're stripped away,

you're any status, any money, any suit, any nice clothes, everything's stripped away. It's just you and a swimsuit and your body. And I don't know if you could share with me, but it seems to me that that kind of thing, the kind of acceptance of that sort of thing, feels to be more of a Scandinavian thing. It feels like in the UK people have got huge hangups about their bodies, you know, and I'm not criticizing that, right? I understand that. But ultimately we've all got bodies. Maybe that is exactly what is actually going on. We have packed ourselves so much up. We never see each other really in a bathing suit. We don't expose our bodies to temperatures anymore.

If we go, that is only in the summer, right? So I think that you mentioned the culture difference also. So in Denmark, I think we have been winter swimming for many years i know that there's only it's only a new trend also in denmark that more people are winter swimming and it's not only for the the wild and crazy ones anymore it's just it's just for everyone and people have finding out but the culture around going into the cold is definitely something that also builds in Denmark around our way of being social together. So I think you're right on that. We have a way of also trying to keep our clubs and we have a social life that is like very engaging. We try to have that. I think we

are struggling to keep it up because loneliness is also increasing also in Denmark and happiness is also decreasing just like the rest of the world. So stress, anxiety and depression are going up also there. So we see an effect all over. So we definitely need this. We need places where you can go and be social, where you don't have to think about status and you don't have to think about status and you don't have to think about how you look or we're just human beings and when you go into the sauna and if you have someone out there has tried that then you know that you are not looking at the other's bodies or anything you don't you are just there you're being either you're being very mindful

sitting in there and just actually releasing everything of your stress, just let that out of the sauna. Eventually, you will learn to do that and find it a peaceful room. But you will also find it very social if you go with your friends. That is a place where you probably don't have to discuss any heavy stuff, but you can if you like to. But you can also just be there and be together. And that connects people. It's just, it's just super fascinating for me as I think of how this

movement is growing and where it's coming from, how all these things play out. Susanna, honestly, I could talk to you for hours. Honestly, I think it's, it's so fascinating, this whole area to try and sort of bring this conversation towards a close. fascinating this whole area to try and sort of bring this conversation towards a close in terms of practical recommendations we mentioned a few already wearing a hat people going winter swimming or going obviously in a shower you're probably not going to wear a hat but winter swimming or going into a cold plunge yourself let's say it's outside there's benefits to wearing a hat isn't there and then if you could also speak to do you need to get your head underwater i think that's really really important so i think that if you you can wear a hat if especially if you think that that you get too cold too easily

and if there's a wind there's a strong wind that could actually determine how long time that you're going to sit in your cold plant and if you And if you can pass the cold shock response. So wear a hat because it also protects your ears from the wind. And especially if you have, I have like my ears always get super easily cold and then I get a bit dizzy. So cold ears and ear infection, if you are like prone to that, then wear a hat because that will protect you. Also, a lot of heat is coming out of your head, right? So I think that is around 80% of our body temperature is actually coming out of our head. So if you put a hat on, then it's more, you can say, controlled to the rest of your body.

So wear a hat is definitely a good thing if you have those kind of issues also. I always take my hands above the water because my fingers hurt and I don't think that should hold people back. So if you think that that will help you, then take your hands up or wear gloves. If it's icy, then do that because then you can stay in the water for a little bit longer. So you can get the benefits even without your hands in yeah even without your head in yeah that's that's great for people to hear actually i think that this is also really important that you you can get the benefits from just putting a hand in the water or hands or feet so in the water you you can get some cold adaptation actually from that there's is actually studies showing from, it's

fishermen who have their hands a lot in cold water, shows that nice research has been done on these fishermen and it shows that they are cold adapted all over their body, but only their hands were actually in the cold water. And I think this actually tells us that the body is like one system. It's not the hand is one thing. It's the whole system. It's all connected. So if you get cold adapted from submerging up to your neck and you don't put your head under, you will get adapted anyways.

I love it. So just doing the washing up in cold water, we're sort of getting all these benefits. I think that's fantastic. Okay. And just to finish off then, what Andrew has named the Soberg Principle was based on a paper I think you published in 2021, which has got like a conclusion for people, isn't it? In terms of for people who are like, okay, Susanna, you convinced me, right? I don't do it, I'm in. For people who are like, okay, Susanna, you convinced me, right?

I don't do it, I'm in. You have some recommendations for the cold in terms of duration and also heat, like sauna. So I wonder if you could just share those for people, please. Yeah. So based on my research, where as I started the conversation telling you that I wanted to find the minimum threshold for where can we get benefits and not have to stay extremely long. So I wanted to do some kind of research where we know from this kind of, you could say, micro-stressing the body, we will still get benefits.

And what the study showed was actually that, and this is shown in winter swimmers who are adapted to winter swimming, they have been winter swimming for two to three seasons before I studied them for one season. But what we saw, when you are cold adapted, and you will get that really quickly if you are new, but when you are cold adapted, you can increase, so you can do your cold exposure.

11 minutes per week is actually enough. And this is in total. I just want to underline that. 11 minutes in the cold water in total per week is actually enough. And this is in total. I just want to underline that. 11 minutes in the cold water in total per week, but divided on two to three days. And on each day, you can do three dips. So you can divide that up in minutes at probably around everything from two to four, five minutes or so per dip. So you don't have to go across that.

You don't have to be in that. You don't have to be in the water for many minutes to get these benefits, this study shows. So 11 minutes per week divided on two to three days and up to three dips. Oh, so once you're adapted, 11 minutes is all you need a week. Yes, exactly. So you can build, when you are new, you just have to, when you are new, you can look at the 11 minutes as a protocol for a method for getting there. And when you get there, you know, well, this is about 11 minutes. It could be 12 for some and it could be 10 for some. It depends on, again, it's individualized. But if you're new and you're not an experienced winter swimmer, it's reasonable to think you don't even need 11 minutes. No, you don't. Well, I need to underline that as well because you will get benefits the first time you go.

You will get benefits already from the beginning. But what I studied was to see what happens if you winter swim a season and you're already adapted. What can we see on the outcomes of activation of the brown fat on your temperature? What can we see from your metabolism? How is that change? How is that better compared to a control group who were not winter swimmers and who didn't get into a sauna, who didn't get these kind of healthy natural stresses to the body.

And I think it's very important to say that this is also like an increasing health. So every time you go, even just for 30 seconds, a cold dip or going into the cold shower, you will have benefits already from the beginning. But when you go up to 11 minutes, that is definitely something that we can say, this is healthy. We can see that in my study. But yeah, so you can try and build that up. And there's also some recommendations

for sauna use as well, right? Yes, it is. And I just want to, as you answer that, I just want to also clarify a lot of the benefits, or perhaps you could explain, a lot of these benefits we've been talking about happen if you just do cold, right? You don't have to also do the sauna. Is that right? You don't have to do the sauna, but this study is performed in the contrast of going into the cold and going into the heat as well. So in the sauna. And the funny thing is actually that the

brown fat is also activated by heat. Oh, wow. Sorry about that. But it is. And that is also why I was like, well, in theory, it would be that the brown fat is not only activated by the cold to make you warmer. It's actually trying to regulate your temperature and trying to make you warmer when you're cold, but also trying to make you colder when you are hot. And that is also proven in studies that the brown fat is activated by heat. So we know that. So that is why I had the sauna with it. So 57 minutes per week in the sauna, also divided on these two to three days, is actually also enough to get these health benefits.

And what I think is funny is that if you divide that on minutes per time you go, you would see that that quite fits well with what we see in the Finnish cohort sauna studies, where we see that if you go up to 19 minutes or with a maximum of 29 minutes, you see health benefits. And when you go longer than that or sit longer in the sauna than that, you will see a decline or a plateau of the benefits, right? Yeah. But if you go two to three times per week in the sauna and you stay under the 19 to 29 minutes, then you will have a profound, I think, very, very profound health results from that.

Because we see that two to three sauna days a week actually decreases your risk of dying by 27%. And if you go four to seven times per week in the sauna, that will decrease your risk of dying by 50%. And I think that that is really strong. That is strong, like, even though it's a cohort study, but they have followed these for 27, 28 years, I think. And the minutes, if you look at that and you compare that with my results, it kind of fits. It fits with the results that we see in my study as well. So if it's a sweet spot, it's definitely a sweet spot, I think. But if we can go a little bit more, I don't know about that,

but I think that future research will find out. Yeah, it's super exciting. I love it that your study has shown concretely what our Scandinavian ancestors have been telling us for years. I think that's a beautiful kind of way to finish off this conversation. I think those recommendations of 11 minutes of cold and 57 minutes of three 19- sessions of sauna for people who have access is very very achievable and for people who don't have access throughout this conversation we

were talking about stop with a cold shower you know we mentioned the immune system benefits of a 30 second cold shower right so i think it's absolutely brilliant susannah it has been such an honor and pleasure to have you in my studio to talk about all of this. I know it's the first kind of long-form conversation you've had. I feel very honored that you've, you know, come over to talk about your work. You definitely teased us a lot at the end there with more work that's going to be coming out. So I hope at some point you'll come back onto the show to talk about some newer research that no doubt you'll be conducting. This podcast is called Feel Better, Live More. When we feel better in

ourselves, we get more out of our lives. So I guess right at the end of this conversation, just to sum up, do you have any final words, final words on how people can use temperature how they can use cold to get more out of their lives so i think that if you don't have access to do a cold plunge in the sea or in a lake or something you can you can definitely use a barrel or you can definitely use some kind of plunge some kind of device where you can just jump in um but you can also use the cold shower because the cold shower is also going to activate your immune response, but it's also going to activate your metabolism and also your brown fat. So you will definitely get some benefits from that.

Not the same as the cold plunge, but you will get some of it at least. Yeah, I think for the cold, that is what I would suggest at least. But you can try and build up the courage to get some kind of device where you can jump in or you can go driving a little bit to get to the cold water. Yeah, fantastic. Susanna, thanks for coming on the show. Thank you for all the research you're doing. And I hope to see you back on the show at some point in the future.

I would love to. Thank you for inviting me. And I'm really honored to be here. Thank you. the future. I would love to. Thank you for inviting me. And I'm really honored to be here. Thank you. Really hope you enjoyed that conversation. As always, do think about one thing that you can take away and start applying into your own life. Will you be giving the cold a go? Well, as well as Susanna's book, Winter Swimming, which is a great resource. If you visit her website, Zanna's book, Winter Swimming, which is a great resource.

If you visit her website, www.soberginstitute.com, you can now book onto her online Thermalist course, where she will take you through how to get going with cold and heat exposure and teach you helpful breathing practices. This course is suitable for beginners and experienced practitioners. And she has very kindly offered listeners of my podcast 10% off the course with the code RANGAN. That's spelled R-A-N-G-A-N. And finally, once we had finished recording our podcast,

Susanna stood over and watched me go through my very first cold immersion in a beautiful brass monkey ice bath. We recorded and videoed the entire thing. If you want to see that 10 minute video, all you need to do is make sure you are signed up to Friday Five, my free weekly newsletter. It contains five simple ideas to improve your health and happiness. And in that email, I share exclusive insights that I do not share anywhere else, including health advice, how to manage your time better, interesting articles or videos that I've

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