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Welcome to Huberman Lab Essentials, where we revisit past episodes to find the most effective and practical science-based tools for mental health, fitness, and productivity. I'm Andrew Huberman, a professor of neurobiology and ophthalmology at Stanford School of Medicine. And now to my conversation with Dr. Susanne Sjoberg. Dr. Susanne Sjoberg, congratulations. Thank you. Very glad to see you here. I have been interested in cold thermogenesis for many years, and you provide so much quality information about this area, which was long considered niche but is now
becoming increasingly popular. So, my first question is: is there a way to determine the best approach to an intentional cold exposure protocol? I mean, is this supposed to cause discomfort? If the temperature is very low and you feel very cold, then you should stay in the water a little longer. So I think you should feel uncomfortably cold. By the time you feel uncomfortably cold, it's a low enough temperature, and you're getting what we call cold shock. Cold shock is the activation of your sympathetic nervous system and the release of catecholamines.
Does this shock mean I have difficulty controlling my breathing? Is this a good indicator? Yes, you could say that, because that's how we define it. You are hyperventilating, meaning your breathing rate is accelerating. This is also exacerbated because you activate the gasping reflex if you are new to this. But if you are adapted, then over time it subsides a little due to adaptation. So, you can train this effect of cold and adapt to it in a certain way Then you won't have that hyperventilation reaction every time you dive into cold water.
It's like building your resilience, building up an adaptation that will make the shock recede a little. Of course, it's always harder at first, but you have to do difficult things, right? You think of cold water and immersion in it as something comfortable. It must be difficult, because that's the point, right? If you're enjoying it, then I think something's wrong. This is wrong. You shouldn't get pleasure from this. What are the differences in the level of impact, short-term and perhaps even long-term, between a cold shower; immersion in cold water up to the neck, which can be ice-cold or just very cold water; by diving headfirst and then surfacing, as people
obviously need to breathe; and just being outside on a cold day in shorts and a t-shirt, or something like that The results vary because these are very different types of cold effects on your cold receptors in the skin. So the more you cover your body with cold, which you do in cold water, because the molecules there are of course closer to your skin, the more powerful the activation of all the cold receptors in the skin will be. This will definitely activate your autonomic nervous system more strongly and faster than walking outside in a T- shirt in a cold wind. But it will also activate your sympathetic nervous system, and therefore lead to increased norepinephrine levels and
brown fat activation. This is a useful type of adipose tissue that is present in our body. When you activate it, it speeds up your metabolism. So it's kind of our first line of defense in the body to maintain body temperature. There are two tissues that can enhance our thermogenesis. Brown fat, which constantly regulates our body temperature, and muscles, which secondarily start shivering, which increases our body temperature. But as soon as you step into a cold shower , you also immediately activate your brown fat. So, theoretically it could be useful for boosting metabolism, since we don't really have any studies showing how much it activates brown fat. So if any researchers want to study this, that would be great.
So it sounds like any form of cold exposure to the skin that people perceive as "cold shock" or discomfort, like "that's a bit harsh," activates brown fat. Do we know what path the signal takes from cold receptors in the skin to brown fat? So, how does brown fat know that we are cold? Cold receptors send a signal to our temperature regulation center in the brain, the hypothalamus, and it receives this message. We have so many cold receptors in our skin that the reaction will be very fast; As they say, if you
immerse your body in cold water, it will happen instantly. So, there will be a rapid increase in the level of neurotransmitters in the brain: noradrenaline, adrenaline, cortisol, and although it's not a lot, they are still present. So you have this rush of norepinephrine, which then immediately activates brown fat. But there's also a direct pathway from the cold receptors in the skin to brown fat, which actually shows that through these different pathways, perhaps this heat-retaining tissue evolved over our evolution as humans to keep us warm and to save us when our skin temperature changes even slightly, keeping us in the right homeostatic balance so that we don't get too cold, but we don't get too hot either
But it seems that brown fat is also activated when our skin heats up. So maybe it's also a temperature regulator in our body. However, the path here is different. I think there is also a third way, directly from the muscles. So, brown fat is also activated even when the muscles start to tremble. Therefore, there is an additional way to maintain our temperature. So muscles and brown fat work together to keep us warm so we don't suffer too much in cold water.
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If you want to try Eight Sleep, go to eightsleep.com/huberman to get up to $200 off their new Pod 6. Eight Sleep ships to many countries around the world, including Mexico and the UAE. Once again: eightsleep.com/huberman to save up to $200. I want to ask about tremors. Um, I heard that shaking causes the release of succinate, which then activates brown fat. Is it known whether it is important to induce tremors? And when should people tremble? I do n't think you should be so afraid of shivering, because as long as you don't get hypothermia, that is, if you don't sit in cold water for too long, there is a so-called "aftereffect"-a decrease in body temperature even after you get out of the cold water.
This always happens to your body because as soon as you immerse yourself in cold water, all your blood vessels constrict to keep blood in the center of your body and keep your vital organs warm. So as soon as you get out, the vessels open up again, the warm blood flows outward, cools, and then returns back to the center, and that, of course, lowers your body temperature. Years ago I heard Wim Goff talk about this temperature drop, and my colleagues mentioned it as well, but this is the first time I've heard it explained so clearly.
Let me make sure I understand this correctly. So, I enter cold water, I get cold, my blood vessels constrict to keep blood closer to the center of my body and keep me alive. I'm leaving. Warming the body allows these vessels and capillaries to expand again. The blood rushes to the surface, but the surface is still cold, so the blood cools, my body temperature drops-that's what you call a fall, and that's what causes the shivering. That's right. Perfectly. And do I understand correctly that shivering activates brown fat, which then warms me up again? Yes. Got it. That's why it's worth ending with a cold one. This is training. This is a workout for all your cells. This is a workout for your muscles.
This is a workout for your metabolism that will increase what is called insulin sensitivity. So, if you can mentally get used to the idea that shaking is like working out at the gym, where you feel, "Oh, this is hard, it hurts a little." Yes, it will hurt, because shaking hurts too, but it's just another way of training your cells. This creates so- called healthy stress. This is called hormesis in cells: the more you expose your muscle cells or brown fat cells to beneficial stresses like exercise, cold, or heat, the better they activate and support your health. As long as the cells are exposed to this,
they stay "in good shape," becoming more resilient, increasing the amount of heat and cold shock proteins to make you more resilient the next time. The same thing happens when you go to the gym. I keep making this parallel because people today know more about training, exercise, and how it affects muscle cells. But this is the same training as immersion in cold water, because this is, you could say, your cold training center. And also your thermal training center when you go to the sauna, as the cells become stronger due to hormetic stress. So, the process is the same, only the practices are different.
What other processes occur at the metabolic and brown fat levels, say, within hours and days of intentional cold exposure? Yes, what happens is that you adapt a little bit each time. You get a little stronger, like during exercise. So every time you dive into cold water, you become more comfortable in the cold with each new experience. You develop your adaptation, which occurs at the metabolic level, namely in brown fat. So you get more brown fat activation.
The mitochondria in brown fat cells become larger and they warm you up more effectively because the body expects you to do it again and prepares for it. The capillaries in your skin also become better at constricting. So, you have a better body barrier, which prepares you for the next time. Your stress response will also subside a bit, so your catecholamine levels will rise less due to the activation of brown fat or muscle.
You will experience a boost in your metabolism, which in turn will improve your insulin sensitivity. And this is confirmed by research. For example, there was an interesting study I found before starting my graduate school, authored by [last name] and colleagues. 2016, which measured insulin sensitivity in middle-aged men and women during one season of winter swimming. During these four to five months of winter swimming, they noticed that after the season, people had lower blood pressure and heart rate, and improved insulin sensitivity. And I find this very interesting, because better insulin sensitivity helps prevent lifestyle diseases, and lower blood pressure is a strong indicator of the level of inflammation in the body.
Since they didn't measure brown fat, I assumed that it might be the missing link, one explanation for the lower levels of inflammation in the body. So, the long-term results could be reduced blood pressure and heart rate, as well as better insulin sensitivity and glucose balance, which is what was shown in my study Is it true that when we just move- I've heard of NEAT, non-exercise thermogenesis -we activate brown fat, or is this stress factor necessary? Is shivering and a cold or heat stimulus required to activate brown fat? Cold is the most powerful stress activator of brown fat, as it is our thermoregulatory organ that reacts first. In fact, it is enough to simply expose yourself or
at least your hand to cold water. Studies have shown that if you just dip your hand in cold water-not that you do it all day or every day, it doesn't have to-it proves that brown fat can be activated just by changing the temperature of your skin. People who work outdoors, move a lot, or constantly change their body temperature will have more brown fat. And its activation will allow you to maintain a higher metabolic rate and better insulin sensitivity. This is also confirmed by one of the studies. So, brown fat can be activated just by changing the temperature of your skin. So walking outside in a T-shirt or wearing cooling vests- studies have shown that even for 10 days, it increases your brown fat. So, you can increase the amount of brown fat by
exposing yourself to cold. You don't have to start with a cold shower or a dip in ice water if you're not ready for that, but even exposure to cold wind has been shown to activate brown fat. Or if you don't want to be awake, you can just sleep in the cool, and you might not even notice it, but studies have proven that sleeping at 19°C activates and increases your brown fat. This excellent 2017 study by Hansen et al. showed a group of subjects sleeping in a room at 24 ° and had a PET-CT scan to see their initial levels of brown fat, the so- called baseline. Then they measured everything again after
a month of sleeping at 19°, and they saw-I find this amazing-just one month of sleeping at 19° under the covers and in the clothes they slept in. So they're under the covers, under the duvet? Under the blanket, yes, yes. Subjects who slept at 19° for a month had increased insulin sensitivity. The next month they slept at 24°, the measurements were repeated, and the readings dropped slightly, and then they slept at 27°, that is, in a fairly warm room for the fourth month, and saw even less brown fat activation and insulin sensitivity. It seems like you're exposing yourself to cold, and brown fat responds pretty quickly because it's very sensitive to norepinephrine, right?
So if you continue to expose yourself to a little bit of cold, you also adapt a little bit, but that's because These little power stations activate cells that absorb glucose and fatty acids from the bloodstream to support thermogenesis. And this will help clear the bloodstream of sugar and a certain amount of fat. So, brown fat can thus reduce our harmful fat, i.e. white fat. We don't want to have too much white fat, but we still need it, of course. This is our energy storage, so it is very important that it is there. We just don't need too much of it. It is located on the thighs, as well as around our internal organs.
So, we can activate brown fat simply by going out into the cold, sleeping in a cold room, or, if you're brave, by diving into ice water. A cold shower will also work. So you can apply different variations of this. It is the exposure to different temperatures that activates brown fat, as it is involved in maintaining our ideal homeostatic temperature balance. That is, to sustain our lives. I would like to clarify about this temperature of 19°C in the room where they sleep. They are under the covers, under the duvet, and you mentioned that they were dressed. The room is 19°C, but the temperature under the blanket may not be 19
°C. Apparently, it is the cold on the face that activates the increase in the amount of brown fat. Is this a reasonable assumption? I think so, because there are a lot of cold receptors on the face, so this is quite enough, and it fits well with studies showing that you can activate brown fat simply by dipping your hand in a bucket of cold water. I conducted this experiment myself in my research to see how well they respond to cold water. It was 4°C water for 4 minutes, and then I measured blood pressure and heart rate to see if there was any activation. I also measured brown fat during this 4-
minute cold exposure using an infrared thermal imaging camera. You usually can't see brown fat activation because it's located deep, around the central nervous system, and its largest depot, as you mentioned, is here, under the collarbones, very close to the surface of the skin. And because it's so close to the skin's surface, I was able to measure it with this very expensive camera. We measured brown fat and saw that within a few minutes there was activation and an increase in temperature due to this activation, in just 4 minutes. So this happens very quickly, and in my study I also measured how deep under the skin the brown fat is. It is located very close to the surface, which indicates that it must be there to keep you and your
internal organs warm. I want to take a short break and thank our sponsor, AG1. I am pleased to announce that AG1 has just released their newest formula-AG1 Pro. AG1 Pro takes the clinically proven AG1 formula, which contains a blend of vitamins, minerals, probiotics and adaptogens, and adds three important ingredients: creatine monohydrate, calcium HMB and zinc carnosine. Each serving contains 5g of creatine monohydrate to support muscle strength, performance and brain health, calcium HMB to repair muscle and reduce muscle breakdown, and zinc carnosine to support and improve the condition of the intestinal mucosa. All three of these ingredients have compelling scientific support, so I really like that they were added to the existing
AG1 formula. As most of you know, I have been taking AG1 daily for almost 14 years. I started taking it long before I knew what a podcast was. This is a great product that has become even better with the new AG1 Pro formula. If you want to try AG1 Pro, you can go to drinkag1.com/huberman for a special offer. AG1 gives away a free bottle of omega-3 with coenzyme Q10 when you sign up for your first subscription. Once again, go to drinkag1.com/huberman to get a free bottle of Omega-3 with Coenzyme Q10 with your first AG1 subscription. I would like to talk about your research. It studied not only the effects of cold, but also sauna, and the combined use of cold and sauna as a way to study metabolism, brown fat, and other indicators. Could you
tell us about your research, what exactly you did and what you discovered? When I started this research in 2016, I wanted to see if we could implement some kind of activity to get people moving too, doing something together or something like that. And it was the cold that made us think: what about winter swimming? We reasoned like this: Okay, winter swimmers probably theoretically activate brown fat, right? But we didn't really understand whether this kind of stress was excessive, insufficient, or what would actually happen. I read the literature. I understood theoretically what happens when you step into cold water, but I fully realized it when I tried it myself. It was very uncomfortable during the process, but once I came out, I felt fantastic. We
went to the sauna, and I did three sessions because I really enjoyed it. I liked the feeling afterwards because all the neurons in the brain are activated, you feel more positive, I felt invigorated, I had so much energy, and I completely understand why people do this to get a charge for the whole day, because I definitely got it. I didn't need to dive three times to feel it. I think once would be enough. I wanted to explore the smallest dose, so to speak, the smallest amount that you could get by with, but still see health benefits. So I recruited winter swimmers who have been swimming for two or three seasons, and they only stayed in the water for one or two minutes. The cold quickly recedes, and you get the activation of the "
rest and digest" system, that is, your parasympathetic nervous system. This is another branch of your nervous system. You get this activation because you're diving into cold water, and when you do that, you activate the dive response, you slow down the body's oxygen consumption, and that's because the body is trying to conserve oxygen so you don't get too cold too quickly. So it's like a survival system in your body. So this survival system is very important to us, of course. It activates, and you will feel it in about a minute or so. I can't be exact because it can be a little different for different people. So after one or two minutes, you will have full activation of both the sympathetic and parasympathetic nervous systems.
They do it two or three times a week, and every time they come, they do three activities, meaning three dives and two sauna sessions. They start cold and end in cold water. What is the temperature in the sauna? About 80°C. And how long do they stay in the sauna? They stayed there for 10-15 minutes, depending on whether they went two or three times a week. And we'll talk about why it's important to end cold-the so-called Soburg principle. How cold was the water in this particular case, on average
, because I understand this is winter swimming outside, so the temperature will vary. It's a very uncontrolled environment for this kind of research, but I wanted to do something that was close to what people can do for free- get out into nature, use it , because nature also has a very beneficial effect on us. It also reduces our stress levels. So, it's within the very cold water range, I would say somewhere from 15 degrees Celsius and below. But in reality, it was no colder than two to four degrees on average when it was at its coldest. So it doesn't have to be that cold to be effective enough to activate our metabolism. So what did you find about changes in brown fat, insulin resistance, or rather insulin sensitivity, and metabolism?
So, we saw that we had different metrics to try to figure out what was actually happening when they were already adapted to cold water, compared to a control group matched on different parameters. We did see that winter swimmers had increased insulin sensitivity. They produced less insulin on all days of the experiment. Besides just cooling them and measuring brown fat on each of those cooling days, so two cooling days and one thermal comfort day, right? So I wanted to measure their insulin levels when they were fasting, meaning they hadn't eaten
for eight hours before the day of the study. And they were completely still, just lying in bed. We measured insulin throughout the experimental day to see what level they were at. And we could see that the winter swimmer had lower insulin production. And also, when they drank a glucose drink-we give it to check before inclusion in the study whether they have, for example, diabetes, so that it doesn't turn out to be spoiling the study. So we check that and see if they have a normal curve. So, we saw that winter swimmers had faster blood glucose clearance. So after two hours, we could see that the level was lower and the curve was going down faster than in the control group. So, despite their lower insulin secretion, they have better blood
glucose clearance, which is exactly what we all want, right? Too much insulin is bad because insulin is more or less a conductor for glucose in the blood. How much cold exposure do people need? How much heat exposure do people need to get these benefits? So, when we added the numbers together, we saw that it ended up being 11 minutes per week. Well, of course, not all at once, but they had two or three visits to the water and sauna a week. So, if you divide that, you get one to two minutes in the cold water, and 10 to 15 minutes in the sauna at a time. And I think this is very similar to what we see in other studies. And I think this fits well into the concept of hormetic stress, or beneficial stress, where you expose cells to
this kind of powerful, very stressful factor that causes them to increase the amount of heat shock proteins, which helps cells repair. This proves that you don't need to be in the heat or cold for too long to benefit from such treatments for your cardiovascular system. Therefore, I think it is important to convey the message that you should not go to extremes, you should not swim for half an hour in cold water.
You can go into the water for one to two minutes per session, but a total of up to 11 minutes per week. And regarding the sauna, my research showed a total of 57 minutes per week. And if we also divide it into these two or three days, then two sessions per day-that's exactly 10-15 minutes. It's a low threshold, but I think it's good, maybe we should have such a goal if people need to strive for something And I think it's actually good to have those guidelines because then you don't overdo it. And if you overdo it, you will deplete your cells, which will also increase your risk of cardiovascular disease.
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say that the flavors we developed together are simply fantastic. Raspberry-yuzu is probably my favorite, but I also like mint, and I love the peach flavor. So I really can't choose just one. I love them all. In fact, I drink at least three cans every day, and you'll often see them on my desk during my podcast recordings. If you want to try Matina, you can go to drinkmatina.com. You can also find Matina at Whole Foods and Sprouts Market chains nationwide. And Matina is now sold at all Earth Bar locations across the country. So be sure to look out for Matina at Whole Foods, Sprouts, and now Earth Bar. So, in addition to looking at blood sugar regulation, brown fat, metabolism, etc., were there any markers that you looked at in the
targeted cold exposure group compared to the control group that would show you that this exposure might have additional benefits, say, for immune system function or for any other function? Yes, we studied inflammation. Of course, we measured blood pressure levels and so on, but in the study we also measured IL-6 to look at an inflammatory marker. IL-6 levels increased, followed by IL-10. This is also well known in the scientific literature. So we measured this, and I think it's really important to look at the effects of cold and heat as factors that reduce inflammation in the body.
And if we can do that, we'll open the way to preventing lifestyle diseases, right? This applies to type 2 diabetes, but also to some mental illnesses such as depression, anxiety, and Alzheimer's disease, which have been linked in studies; Newer evidence shows that inflammation increases the risk of depression, anxiety, and Alzheimer's disease, a neurological disease. So if we can reduce inflammation in the body, we will reduce the number of diseases of modern lifestyle, as well as mental illnesses, which are increasing in number in our time. I think it's really interesting that we can go out into nature and use these natural stressors, and I don't want to sound overly romantic or anything.
It's just the effect of temperature, actually, just cold or heat, which will return our body to its natural state and reset it where homeostasis, balance, has been slightly disrupted. So the body will repair itself in this way, and I think it's great that we can do this just by changing our body temperature. And although people are very afraid to do this, because nowadays we have been avoiding cold and heat for decades, because we insulate our homes better and lead a more sedentary lifestyle. We also sit indoors more. We do n't move around that much. So this modern sedentary lifestyle has made us more sensitive to temperature comfort, just neutral.
Therefore, it is not surprising that obesity rates are increasing. We don't expose ourselves to the natural stresses we used to experience before, until the 70s or 60s, when we started living a more comfortable lifestyle, right? And since the eighties, obesity has begun to increase. We see this from statistics. So I believe that if we can use cold and heat, it increases the hormetic stress in the body. It doesn't have to be anything other than natural stresses to the body that could bring us back to natural balance. Can we talk about what I call the Soberg principle, which is ending the procedure with cold to force the body to warm up on its own and
thereby speed up the metabolism even more? Yes. So when you end up cold, you force your body to warm itself, and that requires activating brown fat and muscle, which is beneficial. This is a great interaction to support your thermogenesis. And it's like exercise, even when you're already at home So you don't need to think of cold treatments, ice-hole diving, or the open sea as an exercise that you do for one or two minutes and it's over. If you end up cold, your body continues to perform the exercise for several more hours. And this not only affects metabolism, but also maintains neurotransmitter activity, enhancing it because your body still feels the cold. So you
need these neurotransmitters to activate brown fat as well. This will make brown fat cells and muscle cells more efficient by increasing the number of mitochondria in the cells, which will then generate heat very quickly. So, if you do this a few times, maybe three, four, or five, you will notice changes: you will feel like you warm up more easily and you can stay warm longer. And this is also what we showed in my study: winter swimmers had higher skin temperatures compared to the control group. So they, they When do they come out of the cold? When they come out of the cold, they just rest, and we tested this on the days when they slept in the lab.
We saw that they had greater brown fat activation and higher temperatures. Probably because they also lose heat. They lose more body heat compared to the control group because they have more vascularized skin due to the contrast of cold and heat. So they lose body heat faster during the day. But is that bad? No, probably not, because it will keep your brown fat and muscles slightly activated. So you will, it should work to keep you warm. Let's say someone only has two days a week for intentional cold exposure. Maybe they don't have access to a sauna, maybe they do. Would you advise them to come in for a minute or two, come out, then come back in for a few minutes,
come out and count that as four, you know, four or five minutes to try to get those 11 minutes a week? Yes, definitely. I think it's the temperature changes that strengthen your cells in your body. So if you can practice short exposures, going out and coming back in, you could say it strengthens your cells because you're forcing them to adapt to the temperature changes. That's really what I keep hearing when you explain this data and all this great research, yours and others': It's not about just freezing. It's about the transition from heat to cold and from cold to heat.
I think if people can get into this idea, they'll have a lot more flexibility, a lot more enjoyment, and a lot more benefit than if they were to think, "Okay, I need to go into X degrees of water for X amount of time for X days," you know, in a very rigid way. constantly. How much and how cold is it? And I mean, it's just, well, because we also don't have studies that show exactly what happens if you just keep the water at five degrees and do that for a month? We may learn a lot more about this in the future , and I, I'm sure it will happen, and I really hope so But I just think that logically changing the temperature up and down, up and down, and you do that with water too, it doesn't really matter what temperature your water is. Then just keep changing it
up and down; it can reach 12 degrees Celsius. You are activating your brown fat anyway. I mean that 12-19 degrees of cold air is enough to activate brown fat. So maybe we don't need to get as cold as many people think and keep adding ice-it's not necessary I don't think it's necessary to constantly expose yourself to such cold, it's worth varying it a bit. Listen, I want to thank you very much for coming here today to talk about your work and the incredible direction it's pointing in, because I think no study is definitive, but your study is truly groundbreaking in the study of intentional exposure to cold and heat. So, first of all, I want to thank you for the work you've done and the work you continue to do, including coming here today to
share your knowledge with me and our audience. So thank you very much. I am very grateful to be here.
