Essentials: Cold & Heat Exposure for Metabolic Health | Dr. Susanna Søberg

Welcome to Huberman Lab Essentials, where we revisit past episodes for the most potent and actionable science-based tools for mental health, physical health, and performance. I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. And now for my discussion with Dr. Susanna Soberg. Dr. Susanna Soberg, welcome. Thank you. So great to have you here. For many years, I've been interested in cold thermogenesis, and you're bringing so much quality information about this area that for a long time, I think was kind of niche and is now becoming more and more mainstream. So my first question, is there any way that we can start to gauge what is the best way to approach a deliberate cold exposure protocol? I mean, should it feel uncomfortable? If the temperature is very cold and you also feel very cold, then you should stay in the water a little bit longer. So I think it's just, you should get uncomfortable cold. So as long as you get uncomfortable cold, it's cold enough, and you get this, what we call the cold shock. So the cold shock is activation of your sympathetic nervous system and this activation of the catecholamines. Does the shock mean that I'm having trouble controlling my breathing? Is that a good gauge? Yeah, you can say so, because that's kind of like how we define it. So you hyperventilate, so you have a faster breathing rate. So that increases also because you activate your gasping reflex. If you are new to this, but if you are adapted, it kind of subsides with time, with adaptation. So what you can do is that you can train this cold exposure and you can kind of like get adapted to it. So you don't have this hyperventilating response every time you go out in the cold water. So this is like building up your resilience, building up your adaptation, is gonna make the shock like subside a bit. So it's always harder in the beginning, but you should do hard things, right? You shouldn't think about cold water and cold water immersion as something that is comfortable. It should be hard because that's the point of it, right? If you enjoy it, then yeah, then I'm thinking something is wrong, it's not right. You should not enjoy it. What are the differences in terms of impact, short-term and perhaps even long-term, between cold showers, cold plunge to the neck? So that could be in ice water or just very cold water. Immersion with dunking one's head and then coming up, because obviously people have to come up for air at some point. And then simply being outside on a cold day in shorts and a t-shirt or something of that sort. So there are different outcomes because they are very different exposures of the cold to your cold receptors in your skin. So the more you can say you cover your body in the cold, which you would do in cold water, because of course the molecules are closer to your skin, you will have a more potent activation of all your cold receptors in the skin. So that one will definitely activate your autonomic nervous system more and rapid compared to going out in a t-shirt in the cold wind, just go for a walk. But that is also something that's gonna activate your sympathetic nervous system, meaning that you will have an increase in norepinephrine and you will activate something called the brown fat. So this is a healthy kind of fat tissue that we have in our body. And when you activate that, that's gonna increase your metabolism. So it is kind of like our first responder in the body to keep our temperature up. There are two tissues which can increase our thermogenesis. So the brown fat, which is like always like temperature regulating our body, and then we have the muscles, which will secondarily start to shiver and that's gonna increase our temperature in the body. But as soon as you go into a cold shower, you will activate your brown fat also immediately. So it could be good also for increasing metabolism in theory, because we haven't really any studies showing how much does actually activate the brown fat. So if someone out there wants to do a study, that would be great. So it sounds like any form of cold to the skin that people register as what you call the cold shock or uncomfortable, like, oh, like this is kind of jarring, activates the brown fat. Do we know what the pathway is from cold receptors on the skin to the brown fat? I mean, how does the brown fat know that we're cold? The cold receptors will send a signal to our temperature regulating center in the brain, so hypothalamus, and that's gonna be taking in this message. And we have so many cold receptors in the skin, so it's gonna be very fast. As you can say, if you immerse the body into cold water, this is gonna be so rapid. So it will have a rapid increase in neurotransmitters in the brain from noradrenaline, adrenaline and cortisol, which is not that much, but it's still there. So you have this increase in noradrenaline, which will then immediately activate the brown fat. But there's also a direct pathway from the cold receptors in the skin to the brown fat, which really shows that because of these different pathways, it shows that it could be that this tissue, to keep us warm, was developed in our involvement as humans to keep us warm and to save us whenever the temperature on our skin varies just a little bit to keep us in that right homeostatic balance so we don't get hypothermic, but also so we don't get hyperthermic, because it seems that the brown fat is also activated when we get warm on our skin. So it's also maybe a temperature regulator in our body, but the pathway is different. I think it's also a third pathway from directly from the muscles. So the brown fat is also activated even though the muscles are starting to shiver. So there's an extra pathway that way to keep our temperature up. So muscles and brown fat are working together to keep us warm so we don't suffer too much in the cold water. I'd like to take a quick break and acknowledge our sponsor, Eight Sleep. Eight Sleep makes smart mattress covers with cooling, heating, and sleep tracking capacity. Eight Sleep just launched the Pod 6, which is their most advanced sleep system. The Pod 6 is half the size of their previous models. It's 20% faster with its cooling and heating, and it has nine times as many sensors for tracking your sleep. The reason why Eight Sleep is so effective at improving your sleep quality and duration is because it helps control your core body temperature. And the reason for that is that in order to fall and stay deeply asleep, your core body temperature has to drop by about one to three degrees. And to wake up feeling completely refreshed and energized, you actually want your body temperature to be increasing in the final hours of your sleep. Eight Sleep automatically regulates the temperature of your bed throughout the night and is monitoring your sleep and dynamically adjusting the temperature of your sleep environment so you get the maximum amount of deep sleep and rapid eye movement sleep. I've been sleeping on an Eight Sleep mattress cover for nearly five years now. And with each new iteration of Eight Sleep, it gets better and better at figuring out what my body needs in order to get the best possible night's sleep. If you would like to try Eight Sleep, go to eightsleep.com slash Huberman to get up to $200 off their new Pod 6. Eight Sleep ships to many countries worldwide, including Mexico and the UAE. Again, that's eightsleep.com slash Huberman to save up to $200. I wanna ask about shiver. I've heard that shiver causes the release of succinate, which then activates the brown fat. Is it known whether or not inducing shiver is important? And when should people shiver? You shouldn't be so afraid of shivering, I think, because the shivering, as long as you don't get too hypothermic, so if you don't sit in the cold water for too long, something called the after drop is when your core temperature decreases even after you get out of the cold water. And it always does that, your body, because as soon as you get into the cold water, all your blood vessels is gonna constrict because you need to keep your blood in your core and keep your vital organs warm. So as soon as you get up, those blood vessels will open again and the warm blood will flow out and get colder and then flow back again into the core. And that's gonna decrease the temperature in your core, of course. Years ago, Wim Hof, I heard him talk about the drop and I've heard colleagues of mine talk about the drop, but that's the first time I've ever heard it explained clearly. Let me make sure I understand this. So I get into cold water, obviously I'm cold. Vessels constrict to keep blood near the center of my body, keep me alive. I get out, the warming up of my body allows those vessels and capillaries to dilate again. The blood goes out to the surface, but the surface is still cold. And so that blood is cooled and then my core body temperature drops. And that's what you're referring to as the drop. And that's what induces shiver. Exactly. Great, and then am I right in thinking that then the shiver activates brown fat, which then warms me up again? Yes. Got it. That's why you should end on the cold. It's training. It's training for all your cells, it's training for your muscles, it's training of your metabolism. And that's gonna increase what's called the insulin sensitivity. So if you can, in your mind, get used to the thought of shivering is just like when you go exercising in the training center and get that feeling of like, oh, this is tough, now it hurts a little bit. Yeah, it's gonna hurt because that's what shivering also does, but it's just a different way of training your cells in your body. It's gonna create what is healthy stress, it's called homeosis in the cells. And the more you expose your muscle cells or your brown fat cells to these kind of like healthy stresses, exercise, cold, heat, exposure, it's gonna make them better at like activating and also at keeping you healthy. So as long as the cells get exposed to this, it's gonna keep them on its toes, you can say, because it becomes more robust, increasing these heat shock proteins and culture proteins in the cells to make you more robust for the next time. And that is also what happens when you go to the training center. And I keep like drawing that parallel because people today know more about, we know more about exercise and what that is gonna do to your muscle cells. But the same kind of like training is also what you do when you go out and into the cold water and submerge into cold water, because that is just your cold training center, you can say that. And also your heat training center going into the sauna because the cells are getting stronger with hermetic stress. So it's the same process, just different practices. What are some of the other things that happen at the level of metabolism and brown fat in let's say the hours and day after a deliberate cold exposure? Yeah, so what happens is that you get adapted a little bit every time you go. So you will like exercise, get a little bit stronger. So every time you go into the cold water for every time you will be more exposed to it, you will feel more comfortable in the cold. So you're gonna build your adaptation, which happens on a metabolic level, which is gonna be the brown fat. So we have more activation of your brown fat. The mitochondria in the brown fat cells are gonna be, you'll have more of those and they will be more efficient at heating you up because it expects, the body expects you to do this again. So you are prepared. The capillaries in your skin will also become better at like constricting. So you will have a better shield of your body to prepare you for the next time. Your stress response will also be subside a bit. So you will have a less increase of your catecholamines. Because of this activation of your brown fat or your muscles, you have an increase in your metabolism, which will then make your insulin sensitivity better. And this is shown in studies. For example, there was this interesting study I found just before I started my PhD, which was from Gibberstormer et al from 2016, where they measured insulin sensitivity in middle-aged men and women during one winter swimming season. During these four or five months they were winter swimming, they saw that they had a lower blood pressure after the season and they had a lower heart rate. And they also saw that they have a better insulin sensitivity. And I think that is very interesting because if you can have a better insulin sensitivity, you can prevent lifestyle diseases and with lower blood pressure, which is a very strong outcome also for telling how much inflammation you have in the body. And because they didn't measure brown fat, I figured that it could be that was the missing link, that was one of the explanations to why we see this less inflammation in the body. So the longer outcomes, the long-term outcomes could be that you lower your blood pressure and you have a lower heart rate. You also have a better insulin sensitivity and a better glucose balance, but that was shown, that is shown in my study. Is it the case that as we're just moving around, I've heard of NEAT, non-exercise-induced thermogenesis. So if we're just moving around that we are activating brown fat or does there need to be this stressor? Does there need to be shiver and a cold stimulus or a heat stimulus to activate the brown fat? So cold is the most potent stressor activator of our brown fat because it's our temperature regulating organ in our body, so first responder to that. So actually just exposing yourself or a hand actually just to cold water. So studies have shown that if you just put your hand in cold water, not that you're going to do that all day or every day or anything, it's not something you have to do, but it just shows that you can activate your brown fat just by getting a temperature change on your skin. People who works outside or move a lot or get in and out of it, like changing the temperature of their body all the time, they will have more brown fat and activating that is going to keep your metabolism higher and your insulin sensitivity study have also shown this. So the brown fat can be activated as soon as you just change your temperature in the skin. So going outside in a t-shirt, wearing cooling vests, also studies have shown this for 10 days, it's going to also grow your brown fat. So you can get more brown fat if you expose yourself to the cold, you don't have to start in a cold shower, you don't have to start in a cold plunge if you're not really ready for that yet, but just exposing yourself to cold wind has also shown to activate your brown fat. Or if you don't want to be like. in this awake state, then you can also just sleep in the cold, and you won't notice it that much, maybe. But studies have shown that if you sleep in 19 degrees Celsius, then you will activate your brown fat, and you will grow your brown fat, so you have more of it. So, this is very nice studies from Hanson et al. from 2017 showed that a group of subjects who slept in a room at 24 degrees and then they made this PET CT scanning to see how much brown fat do they have from the beginning, so what we call baseline. Then they measured again after a month of sleeping in 19 degrees, and they saw, I think it's remarkable, just one month at 19 degrees sleeping there. They had a duvet on, and they were still had clothes on when they're sleeping. So they're under a cover, under a duvet. Yeah, under a duvet. Yeah, yeah. Okay. The subjects were sleeping at 19 degrees for one month, had increased insulin sensitivity. The next month they slept at 24 degrees. They measured this again, and then they had decreased actually a little bit, and then they slept at 27 degrees, so quite warm room actually for the fourth month, and they saw even less activation of the brown fat and also insulin sensitivity. So it seems that you can expose yourself and pretty rapidly the brown fat will respond to this because it's so sensitive to noradrenaline, right? So if you keep exposing yourself to a little bit of cold, you will also get a little bit adapted to it, but that's because the brown fat has grown these more mitochondria in the cells, so these small energy fabrics that's going to activate the cells, and that's going to take up glucose and fat from the fatty acids from the bloodstream to keep the thermogenesis up, and that's going to clear up some sugar, and it's going to clear so in the bloodstream and some fat as well. So the brown fat can in that way decrease our unhealthy fat, which is the white fat, and the white fat is what we don't want too much of, but we still need some, of course. It's our energy storage, so it's very important that it's there. We just don't need a lot of it. So on our thighs and also around our inner organs, that's where it's located. So if we can have activation of the brown fat just by going out in the cold and just by sleeping in a cold room, or if you have courage for it, you can go out and expose yourself in a cold plunge. Cold showers is also going to do the trick. So you can do different variations of this. Just exposing yourself to various temperatures is going to activate the brown fat because it was involved to keep us in a perfect homeostatic balance regarding temperature, so to keep us alive. I want to just get a clarification around this 19 degrees Celsius room that they're sleeping in. So they're under a comforter, a duvet, and you mentioned they had clothes on. The room is 19 degrees Celsius, but the temperature underneath their blanket might not be 19 degrees Celsius. So presumably it's the cold on their face that's activating the increase in brown fat. Is that a reasonable expectation? I think so. Yeah, because you have so many co-receptors in your face, so actually it's enough. And I think it corresponds very well with the studies showing that you can activate the brown fat just by putting a hand into a bucket of cold water. And I did this experiment myself in my studies just to see how well did they respond to cold water. So it was four degrees Celsius cold water for four minutes, and then I just measured blood pressure and heart rate to see do they have like an activation of this. I actually also measured the brown fat during this cold exposure for four minutes with an infrared thermography camera. Usually you cannot really see activation of your brown fat because it's located centrally around your central nervous system. And the biggest depot, as you mentioned before, is up here under the clavicular bones, very close to the skin surface. And because it's so close to the skin surface, I could measure it with this very expensive camera. We measured the brown fat with this, and I could see that after a few minutes that the activation was there, an increase in temperature arose from that activation, just four minutes. So it's very rapid. And I also measured in my study how deep was the brown fat under your skin. So it's very close to the surface, which also shows that it needs to be there to heat you up and heat your inner organs. I'd like to take a quick break and acknowledge our sponsor, AG1. I'm excited to share that AG1 has just launched their newest formulation, AG1 Pro. AG1 Pro takes the clinically backed AG1 formula, which is a blend of vitamins, minerals, probiotics, and adaptogens, and adds three important new ingredients, creatine monohydrate, calcium HMB, and zinc carnosine. Each serving has five grams of creatine monohydrate to support muscle strength and performance, as well as brain health, calcium HMB to support muscle recovery and reduce muscle breakdown, and zinc carnosine to support and improve the lining of your gut. All three of these ingredients have compelling science to support them, and therefore I love seeing them added to the existing AG1 formula. As most of you know, I've been taking AG1 every day for nearly 14 years now. I started taking it long before I even knew what a podcast was. It's a great product and it's now made even better with the new AG1 Pro formula. If you would like to try AG1 Pro, you can go to drinkag1.com slash Huberman to get a special offer. AG1 is giving away a free bottle of omega-3 coenzyme Q10 with your first subscription. Again, go to drinkag1.com slash Huberman to get a free bottle of omega-3 coenzyme Q10 with your first AG1 subscription. I'd like to talk about your study. It explored not just cold, but sauna and the co-use of cold and sauna as a way to probe metabolism and brown fat and other markers as well. If you could tell us about your study, what you did and what you discovered. When I started this research in 2016, I wanted to see if we can do some kind of activity so we can have people move also, go and do something, do something together or whatever. The cold made us think about, well, what about winter swimming? So we were just thinking, okay, winter swimmers must in theory activate the brown fat, right? But we kind of didn't really know was this kind of stressor too much, too little or what will happen actually. I read the literature. I understood in theory what happens when you go into cold water, but I completely understood it when I first tried it. It was really uncomfortable just doing it. But afterwards, as soon as I got up, I felt fantastic. And we went into the sauna and I did three rounds because I just loved it. I loved the feeling afterwards because you have all these neurotransmitters going in your brain and you feel more positive. I feel invigorated. I had so much energy. And I could totally see why people would do this to get energy throughout the day because I definitely had that. I didn't have to do three dips to get that. I think one would be enough. I wanted to study the lowest dose, you can say, the lowest amount that we can get away with, but still see health benefits. So I recruited winter swimmers who have been swimming for two to three seasons and they stayed only in the water for one to two minutes. So the cold subsides very quickly and you will get this activation of your rest and digest system, which is your parasympathetic nervous system. So the other branch of your autonomous nervous system. And you get that activation because you submerge into cold water. And when you do that, you have an activation of your diving response and you will slow down your oxygen consumption in your body. And that is because the body tries to preserve oxygen so you will not get hypothermic too fast. So it's kind of like a survival system in your body. So this survival system is very important for us, of course. So that will be activated. And because of that, you will, after maybe one minute or so, I can't be precise on that because maybe it also varies a bit in humans. So one to two minutes, you will have full activation of the sympathetic nervous system, but also the parasympathetic nervous system. So they do this two to three times per week. And for each time they go, each day they go, they take three rounds of, so three dips and two sauna sessions. So they start in the cold and they end in the cold water. What is the temperature of the sauna? About 80 degrees Celsius. Then how long are they in the sauna? So they stayed there for 10 to 15 minutes. So depending on if they went two times per week or three times per week. And we'll talk about why it's important to end on cold, the so-called sober principle. How cold was the water in this particular, given average, because I realize it's outdoor winter swimming, so it's going to vary. It's a very uncontrolled environment to do this kind of study then. But I wanted to do something that was also very close to something people can do for free, going out in nature and use that and also have the nature like it's a very healthy impact on us. It lowers our stress stress level as well. So it's within the spectrum of very cold water, I would say from around 15, 15 degrees Celsius and down, but it was actually not colder than like two to four degrees on average when it was the coldest. So it doesn't have to be that cold to be good enough and enough to activate our metabolism. So what did you discover in terms of changes in brown fat, insulin resistance, or insulin sensitivity rather, and metabolism? So what we saw was we had these kind of different measures to see what's to try and unravel what's actually going on when they are already adapted to the cold water compared to a control group who was matched on various parameters. We did see that the winter swimmers had an increased insulin sensitivity. They produced less insulin on all the experimental days. So besides from just cooling them and measuring the brown fat on each of these cooling days, there were two cooling days and one thermocomfortable day, right? So I wanted to measure insulin when they were fasting, meaning that they hadn't eaten in eight hours before the study day. And they were completely laying still, not moving, just in a bed. And we measured insulin during the experimental day just to see how, what level are they on. And we could see that the winter swimmer had lower production of insulin. And they also, when they had a glucose drink, so we give them that to test before we enroll them in studies to see if they have diabetes, for example, and not knowing, for example, that that wouldn't, that would like ruin maybe the study. So we test for that and see if they have like a normal curve. So what we did see in that was that the winter swimmers had a faster glucose clearance in the bloodstream. So after two hours, we could see that they had a lower level and it went, the curve went down faster than in the control group. So despite having lower insulin release, they have better blood glucose clearance, which is really what you want, what we all seek, right? You know, excessive insulin is bad, insulin being a more or less a chaperone for blood glucose. How much cold exposure do people need? How much heat exposure do people need in order to extract these benefits? Yeah, so when we then calculated the numbers together, we could see that this was ended up being 11 minutes in total per week. So not in one session, of course, but they had two to three visits to the water and the sauna per week. So when we divide that out, it corresponds to being in cold water one to two minutes at a time, but also in the sauna 10 to 15 minutes at a time. And I think this is very like, also similar to what we see in other studies. And I think it fits very well with what we call the hermetic stress or healthy stress, that you expose the cells to this kind of like potent, very stressful situation, where they increase heat shock proteins in the cells and that will repair the cells. It shows that you don't have to expose yourself very much to the heat or very much actually to the cold to get this healthy benefits from going into cold, going to heat and have healthy benefits on your cardiovascular system. So I think this is very important also message to get out that you don't have to go extreme, you don't have to swim for a half an hour in the cold water. You can go in the water for one to two minutes per session, but go up to 11 minutes per week in total. And for the sauna, my study showed 57 minutes in total per week. And if we also then divide it out on these two to three days and two sessions each day corresponds to 10 to 15 minutes. So it's a low threshold, but I think it's good to have that, maybe we can aim for that if people need to have something to aim for. And I think it's really good to have that because then you don't overdo it. And if you overdo it, you exhaust the cells and that will increase your risk of cardiovascular disease also. I'd like to take a quick break and acknowledge our sponsor, Matina. Matina makes my absolute favorite zero sugar cold brew yerba mate. In fact, I helped create the newest flavors. Listeners of this podcast know that yerba mate is my preferred caffeine source and has been for a long time. That's because yerba provides a smooth energy lift without giving you the jitters and it has many other potential benefits such as helping to regulate blood sugar, improving digestion, mild appetite suppression, and more. And I can tell you that having tried all the different brands of yerba hot and cold, Matina is my absolute favorite. So much so that I became a partial owner in the company. And the flavors we developed together, I have to say, are fantastic. Raspberry yuzo is probably my favorite, but I also like the mint flavor and I love the peach flavor, so I really can't pick just one. I love them all. In fact, I drink at least three cans of them every day and you'll often see them on the table during my podcast recordings. If you want to try Matina, you can go to drinkmatina.com. You can also find Matina at both Whole Foods and Sprouts Market nationwide. And Matina is now being sold at all Earth Bar locations nationwide. So be sure to check out Matina nationwide at Whole Foods, Sprouts, and now Earth Bar as well. So in addition to looking at regulation of blood sugar, brown fat, metabolism, and so on, were there any markers that you examined in the deliberate cold exposure group as compared to to controls that revealed to you that deliberate cold exposure could have additional benefits say for immune system function or for any function for that matter. Yeah, so we looked at inflammation, of course we measure the outcome of blood pressure and so on, but we also measured the IL-6 in the study just to see also an inflammatory, anti-inflammatory marker. So IL-6 went up and it also follows with the IL-10. So that is like also very known in the literature. So we measured that and I think it's very important to think about the cold exposure and the heat exposure as something that then lowers the inflammation in the body. And if we can do that, we will have an open door for preventing lifestyle diseases, right? So for type two diabetes, but actually also for some mental diseases as well. So as known as depression and anxiety and also Alzheimer's disease, which are all associated in research, also newer research showing that inflammation increases the risk of depression, anxiety and Alzheimer's disease, neurological diseases. So if we can decrease inflammation in the body, we will decrease our modern lifestyle diseases, but also these increasing mental diseases that we see in these modern lifestyle times. I think it's very interesting that we can go out in nature and we can use these natural stressors. And I don't want to have it sound very romantic or anything. It's just exposure to temperature, actually, just to cold or to heat, that is gonna trick our body into a natural state again and reset it where the homeostasis, the balance is lost a bit. So the body is gonna repair itself in that way. And I think it's beautiful that we can do that just by changing the temperature of our body. And although people are very scared of doing this, because in our times, we have been away from cold, away from heat, temperature for decades now, since we isolated our houses better and we are more sedentary. We also sit more indoor. We don't move as much. So this very modern sedentary lifestyle has made us more temperature comfortable, just neutral. So no wonder, I mean, that obesity is increasing. We don't expose ourselves to the natural stressors that we did earlier on in our involvement, but also up until maybe the 70s, the 60s, where we started having more comfortable lifestyles, right? And obesity increases in the 80s. We can see that from statistics. So I think that if we can take in cold and heat, it all increases the hematic stress in the body. So it doesn't have to be other than natural stressors to the body, which then could keep us in that natural balance again. Could we talk about what I refer to as the Soberg principle, which is to end on cold in order to force your body to heat itself back up and thereby increase metabolism further still? Yes, so when you end on the cold, you force your body to heat up by itself. And that will require that you activate, you keep your brown fat activated and also your muscles, which is a good thing. It's a good collaboration to keep your thermogenesis up. And that's like an exercise, even when you go home. So in that way, you don't have to think about your cold exposure, dipping in your plunge, open sea or what it is, as just an exercise that you do for one to two minutes and then it's over. If you end on the cold, you have an exercise for your body going on for hours afterwards. And that's not only on your metabolism, but it's also gonna keep your neurotransmitters activated as well and increase that because your body is still cold. So you need those neurotransmitters to activate the brown fat as well. So that's gonna make your brown fat cells more efficient and also your muscle cells more efficient. So increasing mitochondria in the cells, which will then generate heat very fast. So if you have done this for a few times, so maybe three, four, five times, you will notice a switch where you like feel that you get easily warmer and you can keep yourself warmer. And that is also what was shown in my study is that the winter swimmers were physically warmer on the skin compared to the control group. So they- When they are out of the cold. When they're out of the cold, just relaxing. And we tested this on the days where they were sleeping in the lab. So we could see that they had a more activation of the brown fat, a higher temperature. So probably because they also lose heat. They have a high heat loss to the body compared to the control group because they have a more vascular skin because of the contrast of cold and heat. So they lose heat faster from the body during the day. But is that a bad thing? No, probably not because that's gonna keep your brown fat and your muscles a little bit activated. So you will have to, it has to work to keep you warm. Let's say somebody only had two days a week to do deliberate cold exposure. Maybe they don't have access to a sauna. Maybe they do. Would you suggest that they get in for one or two minutes, then get out, then get back in for another couple of minutes, then get out and call that for four or five minutes to try and get to that 11 minutes total per week? Yeah, definitely. I think the changes in temperature is what is strengthening your cells in the body. So if you can do the short amount of exposure and then get out and get back in, that is gonna, you can say, strengthen your cells because you are challenging them to adapt to changing temperatures. That's really what I keep hearing coming through as you explain these data and all these beautiful studies, yours and others, is that it's not really about getting cold. It's about going from warm to cold and from cold to warm. I think if people can internalize that idea, that they're going to have a lot more flexibility, a lot more fun and get a lot more benefit, as opposed to thinking, okay, I need to get into X degrees of water for X amount of time on X number of days in a very rigid way. All the time, how much and how cold. And I mean, it's just like, well, because we also don't have studies showing exactly if you just keep five degrees in your water and you do that for a month, then what happens? Maybe in the future, we will know much more about this and I'm sure it's gonna come and I really hope so. But I just think by logically changing that temperature up and down, up and down, and you also do that in your water, it doesn't really, it's not that important what temperature you will have your water then, then just keep changing it, going up and down. It could be all up to 12 degrees Celsius. You're gonna activate your brown fat anyways. I mean, 12, 19 degrees cold air is enough to activate your brown fat. So maybe we don't have to go as cold as I think many people think and putting ice even all the time. You don't have to. It's not, I don't think it's necessary to expose yourself to that cold temperature all the time, but vary it a bit. Well, Sunna, I want to really thank you for coming here today to talk about your work and the incredible direction that it points to because I think that no one study is definitive, but your study really, again, stands as a landmark in the landscape of exploring deliberate cold exposure and heat. So first of all, I just want to thank you for doing the work that you've done and for the work that you continue to do, which includes coming here today to share knowledge with me and our audience. So thank you ever so much. I'm very grateful for being here. ♪♪