How to Use Cold & Heat Exposure to Improve Your Health | Dr. Susanna Søberg

This section identifies the interview's central physiological claims and keeps the speakers' qualifications attached to them. ANDREW HUBERMAN: Welcome to the Huberman Lab podcast, where we discuss science and science-based tools for everyday life. I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. Today, my guest is Dr. Susanna Søberg. Dr. Susanna Sjoberg completed her doctoral thesis work at the Center of Inflammation and Metabolism and the Center for Physical Activity Research at the University of Copenhagen in Denmark. Her research has focused on how deliberate cold exposure and deliberate heat exposure can be used to enhance human metabolism. She is the first author of a seminal study which discovered the minimum thresholds for deliberate heat and deliberate cold exposure for increasing brown fat thermogenesis, which is essentially a mode of increasing heat production and metabolism in the body, and for establishing actionable protocols that can be used outside of the laboratory to improve metabolism and human health. Dr. Søberg's research was published in the journal, Cell Reports Metabolism, in 2021, adding to a long and important history of research focusing on the role of cold and the role of heat in altering various aspects of the body's physiology, including hormone health, metabolism, and changes in neurotransmitters, such as dopamine and epinephrine. In fact, today's discussion with Dr. Søberg focuses on the role of deliberate heat and deliberate cold exposure on metabolism, but it also includes discussion of the effects of cold and heat on things like neurotransmitter production, namely dopamine, and epinephrine, and norepinephrine, the so-called catecholamines, which strongly impact mood and metabolism. In addition, Dr. Søberg answers many common questions about deliberate cold and deliberate heat exposure, including, for instance, the difference between cold showers versus cold immersion up to the neck versus total body cold immersion, including whether or not going back and forth between heat and cold changes fundamentally the way that heat and cold impact the metabolism, hormones, and neurotransmitter production. And we talk about almost every single nuance and variation on deliberate cold and deliberate heat exposure protocols as it relates to the underlying science. In particular, how cold receptors at the level of the skin are impacted versus cold reception and perception at the level of the brain and how all of that impacts systems of the brain and body, relating to mental health, physical health, and performance. Based on her scientific research and academic training, as well as her understanding and use of deliberate heat and deliberate cold exposure protocols, Dr. Søberg is considered one of the world's leading experts on these topics. In fact, she is the author of a recent book entitled "Winter Swimming," which is, I have to say, a terrific book because it breaks down chapter by chapter the different aspects of deliberate heat and deliberate cold into its various constituent parts, including cold acclimatization, the cold shock response, dangers and safeties of cold water, the impact of cold and impact of heat on various aspects of human health, as well as specifics relating to sauna, versus ice, versus cold swimming, showers, et cetera. It's a very thorough read and a very easy and accessible read that if you're interested in deliberate cold or deliberate heat exposure or both, will allow you to embrace those protocols with the greatest degree of confidence that you're going to obtain the specific endpoints that you're interested in and to do so safely. Before we begin, I'd like to emphasize that this podcast is separate from my teaching and research roles at Stanford. It is however part of my desire and effort to bring zero cost to consumer information about science and science-related tools to the general public. In keeping with that theme, I'd like to thank the sponsors of today's podcast.

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The evidence is presented as the guests describe it: the article distinguishes measured findings from hypotheses, observations, and unanswered questions. And now, for my discussion with Dr. Susanna Søberg. Dr. Susanna Søberg, welcome. SUSANNA SØBERG: Thank you. ANDREW HUBERMAN: So great to have you here. I feel like I should give a little bit of the backstory of how we got connected, which was that for many years, I've been interested in cold thermogenesis. It was the topic of my senior thesis in college. And I've of course followed the popularity of Wim Hof. And we've had Dr. Craig Heller, my colleague from biology department at Stanford, who works on cold and its impact on physiology and sports performance. So, for a long time, I'd been interested in this area. But there's been a real lack of new, let's say, high profile, quality scientific information in terms of how, for instance, cold plunges and sauna, how that impacts human physiology. I know there's been some information out there, but it's been sort of scattered. And then a little over a year ago, I see this paper in Cell Reports Medicine and was immediately struck. First of all, the fact that it was in Cell Reports Medicine. I've been on the Cell Press editorial board for a long time now. So, press journals are, of course, phenomenal journals. And the title and the content of the paper was directly in line with the sorts of practices that people are very curious about and then are starting to emerge. Things like sauna, cold plunges, and there was your name first on the author list. And I reached out to you through social media. And we've done a little bit of live content there together. And I've been tracking what you've been doing in the world in terms of your book, and talking about the results in your manuscript, and talking about the science and impact of deliberate cold exposure and sauna. And I have to say that it's been a wonderful and remarkable thing to see, and you're bringing so much quality information about this area that for a long time I think was kind of niche and is now becoming more and more mainstream. So, I'm going to start off with a thank you for being here and a thank you for the work that you've done. And I'm looking forward to talking to you about it today. So, my first question, to get things started, is what is happening when we get into an uncomfortably cold environment? So, for instance, if I'm really hot on a hot day, jumping into a cold pool feels really good. But if I'm already kind of at room temperature, I'm a little bit chilly, getting into that same temperature of water doesn't feel so good, right? There's a shock there. So, if you could just walk us through what happens when we get into uncomfortably cold water, whether or not it's by way of shower or cold plunge at the level of our physiology, and if you'd like, our psychology.

The closing material emphasizes boundaries and safety. It records the concrete cautions in the source rather than adding generic medical advice. I think that's a good place for us to start because I think it will orient people to their own experience if they do that. And for those that haven't done it, it might start to peel back some of the layers as to what the underlying mechanisms of cold are. SUSANNA SØBERG: Yeah. Thank you for that question. It's really good to just address what actually happens in our physiology when we get cold, and you can get cold in many ways. So, you can just head out for the one that gives you the most potent stressor, which is submerging into cold water. But you could also go in outside in the cold wind. That's also going to activate your sympathetic nervous system. So, get all these neurotransmitters going in your body and so your catecholamines. Let's just address that we are taking a cold plunge, for example. So, if you are very hot, for example, before you go into the cold water. It's going to feel less stressful. But the temperature difference from your skin to the cold is definitely going to give you a shock, but your core temperature is warmer, and that's going to feel a little bit better. So that's why when people go into a sauna, for example, and go out and into the cold water, they can do it easily, easier than if they were cold beforehand. ANDREW HUBERMAN: Could I just ask you a few questions? So, you mentioned the sympathetic nervous system, which for people listening who aren't familiar with that, is the branch of our nervous system that's responsible for creating accelerations and heart rate, feelings of alertness, it's accompanied with stress and the stress response. But it's accompanied with waking up in the morning for that matter. So, it's not always about stress. And then you mentioned the catecholamines, which are dopamine, epinephrine, and norepinephrine. So maybe a little bit later, we'll talk about those individual neurotransmitters. But you raise a really important point, which is something I get asked about a lot for people that are curious about using deliberate cold exposure, which is how cold should the water be. And I know it's very hard to give a straight prescription for that because I think it boils down to what you just said, which is it's really the difference between your current temperature and really the temperature at the surface of your skin and the temperature of the water. So, if you're very warm, getting into cold feels good. If you're already cold, getting into more cold feels stressful. Is there any way that we can start to gauge what is the best way to approach a deliberate cold exposure protocol? I mean, should it feel uncomfortable? And that leads into the question of how do we balance the discomfort with the amount of time that we spend in? So, for instance, if it's just a little bit uncomfortable, will spending more time in the cold get us the same benefit as getting into very uncomfortably cold water for a very short period of time?

The closing material emphasizes boundaries and safety. It records the concrete cautions in the source rather than adding generic medical advice. SUSANNA SØBERG: Yeah. It's a really good question. And I definitely think that this could be a future study on this as well to really unravel what kind of protocols are the best way or also for which outcomes, of course. So, if the temperature sure is very cold and you also feel very cold, then you should stay in the water a little bit longer. So, I think you should get uncomfortable cold. So as long as you get uncomfortable cold, it's cold enough, and you get this what we call the cold shock. So, the cold shock is activation of your sympathetic nervous system and these activation of the catecholamines, which you just mentioned before. ANDREW HUBERMAN: Does the shock mean that I'm having trouble controlling my breathing? Is that a good gauge?

This section identifies the interview's central physiological claims and keeps the speakers' qualifications attached to them. SUSANNA SØBERG: 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 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. It's going to make this shock like subside a bit. So, it's always harder in the beginning, but you should do hard things, right? It's not something that we-- you shouldn't think about cold water and cold-water immersion as something that is comfortable. It should be hard because that's the point of it, right? If you enjoy it, then yeah, then I'm thinking something is wrong, is not right. You should not enjoy it. ANDREW HUBERMAN: Well, this is an important point that you're making because I think that many people shy away from deliberate cold exposure because it's uncomfortable in a way that at least from my experience is very different than the discomfort of exercise. Because with exercise, for instance, if running fast and breathing hard is uncomfortable, you can slow down or walk. If lifting weights is uncomfortable, you can remove some weight, or reduce the number of repetitions, or stop. With deliberate cold exposure, I suppose you can be sort of halfway in halfway out of the water or partially underneath the cold shower, but it's very hard to titrate and adjust the level. It's kind of all or none. And I've seen-- actually, I can tell this by anecdote I've done some work with military special operations. I won't say which country. This was outside the US. And these are very tough individuals. They're used to going without sleep and doing hard, high consequence, high risk kind of work. And they were asked to do some cold-water exposure training, and I was there that day, and it was remarkable. About a third of them just went straight in and just kind of grinded through it. They looked stoic anyway to me. There were a few whimpers, no cries. About a third talked a lot, and you could tell that they were agitated and anxious, but they made it through. And then about a third of them just simply would not get in past their knees or thighs. It seemed like they were just dreading the whole experience. Some actually didn't actually go in completely. Which was really surprising to me in that you couldn't tell based on their physical appearance or anything else about them, they're all high performers, as to who would have this response. So, it seems like people vary tremendously in terms of their ability to embrace the discomfort of the cold. From your studies, is that your experience as well, or are there these weird mutants who seem to just love going into the cold for the first time? SUSANNA SØBERG: So, some people just feel better in the cold, and some people dread the cold even more. And you can say the more people are pushing the cold away, they might feel the cold pain even more. So, they would definitely-- people who are, maybe the soldiers you just talked about, some of them might be already adapted to the cold. So, if they are not scared of the cold, they go out, and they embrace the cold in a better way. It could also be that some people have a more sensitive nervous system. And when you are a bit sensitive to the cold, you will, of course, try to get away from it, right? And you also feel the pain more if you avoid it. So, the more you avoid the cold, the more pain painful it will feel when you go into it.