The Science Behind Cold And Heat Therapy And How To Do It For Maximum Benefit

Mark Hyman, MD

Dr. Mark Hyman is leading a health revolution—one focused on using food as medicine to support longevity, energy, mental clarity, happiness, and so much more. Mark Hyman, MD is a practicing family physician and an internationally recognized leader, speaker, educator, and advocate in the field of Functional Medicine. He is the founder and director of The UltraWellness Center, Founder and Senior Advisor for the Cleveland Clinic Center for Functional Medicine, a fifteen-time New York Times best-selling author, and Board President for Clinical Affairs for The Institute for Functional Medicine. He is the founder and chairman of the Food Fix Campaign, dedicated to transforming our food and agriculture system through policy.

He is a co-founder and the Chief Medical Officer of Function Health. He is the host of one of the leading health podcasts, The Dr. Hyman Show with 150+ million downloads. Dr. Hyman is a regular medical contributor to several television shows and networks, including CBS This Morning, Today, Good Morning America, The View, Fox, and CNN.

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Full Transcript

Automatically generated. Please forgive any typos or errors in the following transcript. It was generated by a third party and has not been subsequently reviewed by our team.

Introduction:
Coming up on this episode of The Doctor's Farmacy.

Susanna Soeberg:
You can go into something this simple, cold water. You will have an increased focus, increased drive, which will give you motivation for the rest of the day to pursue whatever you want to do. And you get a more positive angle to your life even, because you also increase oxytocin, which is also a stress hormone, it's also what we call the love hormone.

Dr. Mark Hyman:
Welcome to The Doctor's Farmacy. I'm Dr. Mark Hyman. That's Farmacy with an F, a place for conversations that matter. And if you've ever heard about hot and cold therapy, the benefits of saunas, cold plunges, you're a little confused about what it is, why it works, why you should do it, or why you shouldn't do it, you're going to love this podcast because it's with the world's expert on hot and cold therapy, Susanna Soeberg, who has a PhD in metabolism. She specializes in functional breathing, cold and heat exposure for health optimization. She's a founder and the CEO of the Soeberg Institute, where she teaches how to stress up to stress down.
And you might have heard me talking about hormesis in my recent podcast. Little stresses that doesn't kill you, that makes you stronger. Well, this is exactly what we're talking about. And it's using natural stressors to activate your body's own innate healing systems. She's created an incredible amount of research looking at what we need to do, how we need to do it, what works, what doesn't work, what it does to our bodies, what's the minimum amount, how much cold, how much heat to get all the benefits. We're going to talk about all that today. Getting into the nitty-gritty.
She's an international author of Winter Swimming, which sounds like it'll be a hard sell to people. "Okay, let's go winter swimming." But anyway, much better hot swimming in the beach in the summer, which was actually a number one bestseller, so people must have loved it. It's translated into 13 languages and we are going to get deep into the science of hormesis, hot and cold therapy, what to do, how to do it, and why it is so important for your health. And it's why I actually included a whole chapter on hormesis in my book, Young Forever, which if you haven't gotten a copy already, get a copy. So welcome, Susanna.

Susanna Soeberg:
Thank you very much, so much for inviting me as well. And thank you for that lovely introduction. I'll see if I can live up to it at least.

Dr. Mark Hyman:
Okay. Well, you're in Denmark, which is definitely a cold place in many parts of the year, and you've somehow found your way to study this topic, which was sort of like, I would say not much attention was paid to it throughout medical science, and yet you've created a career out of understanding the biology of what happens and why it's so important.
So let's talk about this because seems like cold plunges are the latest craze. Saunas are popping up everywhere. It's a huge wellness trend, but it's something that's been around for a long time. Native American sweat lodges, the Finnish saunas, the Polar Bear club. It's kind of been a fun thing. I actually went to Antarctica and I jumped in the Antarctic Ocean. It was very, very cold. I only stayed in for a minute or two. They had me by a rope in case I froze to death and they would pull me out.

Susanna Soeberg:
Well done.

Dr. Mark Hyman:
Thank you. So tell us how did, just at a high level, how do cold and hot therapy have this massive potential to increase our health and our longevity even, as a strategy for enhancing our wellbeing and our lifespan?

Susanna Soeberg:
Yeah, I love that question. It's a really good question. Taking it from the top, just actually, why should we actually do this and why is it good for us? So overall, said that I think that down the road when I have read a lot of literature and also done my studies, I kind of realized that this is actually a good way to prevent lifestyle diseases. So it protects the body from getting inflamma, inflam... It protects the body-

Dr. Mark Hyman:
Inflamed.

Susanna Soeberg:
Thank you. It protects from inflammation. That's right.

Dr. Mark Hyman:
Sorry, I don't speak any Danish, so you're doing great.

Susanna Soeberg:
Thank you. Yeah. So inflammation will decrease when you stress the body, whether you stress it in a cold way with cold stress or with heat stress, you will lower the inflammation if you continue doing this. So from the first time that you go, you will already be starting this process because you are creating what you just mentioned before, the hormetic stress in the cells, which builds the cells stronger, but also the whole system is going to be activated, your immune system, and more white blood cells will come out in your system because of the shock and also the stress hormones and which eventually also then, because of the increase in metabolism, which I know we will get back to that. What is that and how does that work? But all in all, this will lower your inflammation in the body and it will lower your stress level.
So you will have lower blood pressure, you have lower heart rate, and you have done this for a while. And that is actually what we measure as an outcome for having a risk for cardiovascular diseases and lifestyle diseases such as type two diabetes. But also, inflammation is associated with neurological diseases such as depression and Alzheimer's disease. So what I wanted to do in my studies and why I actually went back to university after working at the hospital, I was like, "Okay, so many sick people here and the pile is getting bigger." I wanted to go around that pile and see if I can find out some way to give people some advice. So I don't know, this pile doesn't get bigger. I just wanted to figure out if I could give advice before they actually get sick so we could prevent disease and what keeps people healthy. So hormetic stress was actually what I went for. So yeah, the brown fat, which I know we would get into. But this could prevent lifestyle diseases and mental diseases.

Dr. Mark Hyman:
This is just remarkable what you're saying. Essentially, there's this simple, basically free, almost free therapy that has the potential to deal with inflammation in the body, which we now know is the biggest driver for almost all chronic diseases. Not to mention autoimmunity, not to mention aging itself as an inflammatory disease. And so, we have this incredible technology that's been around for thousands of years that we've been using to help our bodies stay healthy. And I think of these as survival pathways. When we were in these non perfectly thermo regulated environments when we were out there hunting and gathering and we didn't have 68 degree temperature controlled environments all the time, and we had to deal with these extreme temperatures of heat and cold. And when we had that, it seems to activate this ancient longevity pathway.
And I think the inflammation story is so important. You mentioned mental health because it's not just increasing dopamine and other neurotransmitters. Actually, your brain is inflamed when you're depressed. And so this is actually an interesting doorway and I just want to share a little anecdote. I'm going to get more into the details. I had chronic chronic fatigue syndrome when I was in my 30s from mercury poisoning. And I was really sick, I was super inflamed, my gut was inflamed, my muscles were inflamed, I had myositis, I had brain fog, I had constant aching and pain everywhere, and I was just this mess of inflammation.
And on one of the only things that could actually help me get relief for a short period of time was doing a sauna and a coal plunge or doing them over and over again. And it was kind of like a miracle drug that nothing else worked. It wasn't curing me, but it literally helped me get some relief. So I know from firsthand experience, I mean it's great to do when you feel healthy already and it just enhances your health, but even if you're already sick like I was, it was such a powerful intervention and it really is something I've used for decades to help me stay healthy, feel good, to reset my nervous system and to change my biology. So it's super powerful.

Susanna Soeberg:
I completely understand. Did you have pain relief also?

Dr. Mark Hyman:
Absolutely. Pain relief, cognitive, my brain fog lifted, my muscles stopped hurting.

Susanna Soeberg:
Makes sense. Yeah.

Dr. Mark Hyman:
I felt like a normal human being for a few hours afterwards. And then my mercury poisoning, I had to deal with the mercury, the cause of it all. But eventually it was so powerful. Now, want to get into the science of this. We're going to get into hot and we're getting into cold, but we'll start with cold. You're really one of the leading researchers in this, if not the top researcher. So let's break down what happens in your body when you go into cold immersion and what are the effects on your biology? And we'll go through all of them, including physical and mental. But I also want you to talk about what is the right temperature and dose, because I think people are like, "Oh, that's scary. I don't want to do that." But actually, it may not be as much as we think we need. So let's talk about the science of it. What does it do to us? And then let's talk about the drug dose and delivery and the duration.

Susanna Soeberg:
Duration. Let's do that. Yeah, let's have it as a cliffhanger for now.

Dr. Mark Hyman:
Yeah, yeah.

Susanna Soeberg:
Okay. So let's start with what happens when you go into the cold water. So as soon as actually you stand there on the jetty or on the beach or wherever you plunge in your cold plunge in your garden, as soon as you take off your robe, off your clothes, you'll stand there in the cold wind and you'll have a starting your activation off your sympathetic nervous system, so your fight or flight system. Because the co-receptors on your skin is going to send a signal to your brain in your temperature regulating sensor in the hypothalamus where there will be this center which always regulate and sends whether you are getting a little bit too hot or a little bit too cold.
And from that, it would send out these signals, so stress neurotransmitters in the brain, but also hormones which are noradrenalin and adrenaline, cortisol also a little bit, not so much actually, but it's going to activate your stress system. And that's going to make your heart rate goes up a little bit, but also your blood pressure just a bit. It's not much, it's just between 11 to 19 millimeter-

Dr. Mark Hyman:
A mercury.

Susanna Soeberg:
Mercury, thank you. And which is not so much. And studies actually shows that this only happens with the heart rate going up, and also the blood pressure going up a little bit, only happens if you are a new winter swimmer. And when I say winter swimmer, it's just because that is the term I use the most here in Denmark 'cause that's what we call it. But what I really mean is cold water immersion. You could call it plunging, you could call it... It's just going into cold water and you can use the way you want to, what suits you in your life. But here in Denmark, we have the open sea, so we call it winter swimming. And that is why my book is called that.

Dr. Mark Hyman:
Yeah, yeah.

Susanna Soeberg:
Just to explain the terms. Okay. So you have an activation of your sympathetic nervous system. When you are new, it's more of course. And when you then-

Dr. Mark Hyman:
You mean when you first first start practicing cold immersion therapy, you start have a more extreme reaction in your physiology?

Susanna Soeberg:
Exactly. And that's of course going to activate, when you then go into the water, that's going to activate full on your sympathetic nervous system. But because of the diving response, when you submerge your body into the cold water up to the neck, it's going to activate your diving response. And your-

Dr. Mark Hyman:
And what's that?

Susanna Soeberg:
Your diving response is because you submerge the body into cold water and that's going to activate your parasympathetic nervous system. So it's actually also your vagus nerve. So that's going to make your system go a little bit into a conflict. So the heart rate really wants to go up because of the activation of the sympathetic nervous system, but the diving response, because of the activation of the digested rest system, will make the heart rate and blood pressure go down. So there's a little bit of a stress in the body in the first half a minute to a minute, around that time, especially if you are new to this. So if you are trained and you have done this for a while, your body gets more adapted to it and you won't have as much of an activation of the sympathetic nervous system as you would if you were completely new.

Dr. Mark Hyman:
So you'd have more of a parasympathetic response?

Susanna Soeberg:
Yeah, because-

Dr. Mark Hyman:
If you do it over a period of time. Yeah.

Susanna Soeberg:
Yeah, exactly. So you get adapted to this. And that's also because of some physiological processes that is happening in the body. And you can divide them into three processes, which is the metabolic process where the activation of the brown fat in the body is this healthy kind of fat that we have. I'm not going to go completely into that right now because it's not-

Dr. Mark Hyman:
We're going to come back to brown fat.

Susanna Soeberg:
Yeah, we are, but that's-

Dr. Mark Hyman:
It's a good kind of fat.

Susanna Soeberg:
Yeah, it's the good fat. And then there's a bad fat, that is the white fat, and we want to activate the good fat so we can get rid of some of the white fat. So that's a good thing when you go into the cold water and you activate your sympathetic nervous system because that is going to increase noradrenaline, activate the brown fed and then you heat up. We're going to go more into that, but that's one of the process.

Dr. Mark Hyman:
Well, here's just to stop for a sec. So just to unpack it because you're going fast. So the diving response essentially is to help you survive if you fall in cold water because it slows everything down and slows your metabolism down. It slows your heart rate down it. It's why people who have hypothermia, even when they seem to be near death, can be revived because everything is conserved.

Susanna Soeberg:
Yes.

Dr. Mark Hyman:
Right. So that's actually a good thing.

Susanna Soeberg:
It's a good thing. Yeah. That's because it's cold. Yeah.

Dr. Mark Hyman:
Yeah. But that's sort of what the diving response is for people who don't know what that is. And it's a powerful survival mechanism.

Susanna Soeberg:
It is. Exactly. Yeah. So the diving response only activates when you're submerge into water. So not in the cold shower, for example. So when you do that, you have this activation of all your neurotransmitters in the brain, and you will have this activation of the parasympathetic nervous system if you are able to stay there longer than the cold shock. And when that subsides, it takes about a minute or two, then you have the full activation of the parasympathetic nervous system. And if you can get over to that and you can sit long enough in the water for that, you have to rehearse that. People should go very slow and this is not what you do-

Dr. Mark Hyman:
The first 30 seconds are the hardest and then it gets easier.

Susanna Soeberg:
Yes. Then it gets easier, but it goes quick, actually. Studies show that already after the third time actually, you go into cold water, and this has been tested in studies, where they took subjects and put them into water, and already after the third time, they could see a lower hyperventilation in the subject. So they found that they didn't hyperventilate as much. So the heart rate and blood pressure went down. But it's also because of people get a little bit anxious about going into the water. "What is this? Is it dangerous or is it...?" So the first thing that happens is the activation of your autonomic nervous system.

Dr. Mark Hyman:
And then the metabolism, the brown fat is the next part. Right? So then tell us about the brown fat, what it does, why we have it, why it's important. Because there's a fascinating group of Tibetan practices called Tummo. You probably know about this, right? Tummo. You know about the Tummo practices, the drying of the of the sheets. So the Tibetan monks, when they would go through their initiation who lived up behind the Himalayas, they would have these sheets dipped in ice water in the cold Himalaya winters, and they would be wrapped themselves in the ice sheets and they would have to meditate and activate their brown fat. Of course, they didn't know they were doing that. They were doing ancient breathing and breath practices, activate their brown fat and dry the sheets on their body. And then once they got good at that, they were actually given the opportunity to go up into the snow basically with just underwear on and a loin cloth and have to sit overnight and keep themselves warm overnight in the winter. So that's the power we have within us that people don't realize. You didn't know about this?

Susanna Soeberg:
I didn't know that story actually. But it's very good. Thank you.

Dr. Mark Hyman:
Oh my God, it's amazing. You should Google it. It's called a drying of the sheets or Tummo. It's an ancient Tibetan practice.

Susanna Soeberg:
It sounds like it's about the brown fat because it's not like you can say so intuitively we have known about how the body works and how we can heat up from the inside. We just didn't have the science around it. If you look back to our ancient Greeks, so Hippocrates and Socrates, they said that they advised people to go into the cold water and go into the hot water because that's going to make your blood or your fluids, what is that called?

Dr. Mark Hyman:
Fluid. Your body fluid.

Susanna Soeberg:
Fluid. Yeah, your body fluids flow easily in the body if you do that. So they didn't really know exactly. They didn't have the science to back up what they were really saying, but they intuitively knew that this was already going on. So it sounds like the story you're telling is because people can feel that they heat up when they get cold. That is also what my science show, that you actually get physically warmer from activating your brown fat and doing this kind of activity going into the cold and going into the heat. But you get warmer.

Dr. Mark Hyman:
Yeah, it's true. Seneca 2000 years ago, was a Stoic philosopher, was a cold water enthusiast. He inaugurated the first of every year with a cold plunge in the Virgo Aqueduct. And Thomas Jefferson used a cold foot bath every morning for 60 years and died at 83, which was old back then. So it's fascinating that there's actually, Hippocrates also talked about cold plungers. This is not a new idea.

Susanna Soeberg:
It's not a new idea. They called this thermalism. That's why I actually called my school or my course, I call it Thermailst or Thermalism Cure. Because that's a tribute to them because they already them saw this. And today, we have some signs to back it up.

Dr. Mark Hyman:
So you have this parasympathetic, sympathetic shift in your body. And that actually, even though it seems like a stress eventually, it actually can help your nervous system calm way down. Right? And mitigate the effects of stress. I want to come into the brown fat, but I want to talk about this inflammation and also the mental health part 'cause I think that's important, and we'll dive deep into the metabolism conversation. So with the cold plunge, you get a release of other neurotransmitters and it changes your cognitive performance and your mental health. And can you talk about that? And then we're going to talk about inflammation, then we're going to talk about brown fat. Okay?

Susanna Soeberg:
Okay. Great. So the mental health part. Yeah. So what is great, or you can say what we actually need today is to learn how to stress up to stress down. And that is what happens when you go into the cold waters. So what happens is you get this increase of neurotransmitters in the brain of noradrenaline, which gives you focus and drive. And it actually increases up to 2.5 fold within just a few minutes. And I think that is amazing. And we knew this already back in the '70s, which is shown in studies of physiology studies back then. So it's not kind of new news or anything, it is just today we can take the science together and we can make a better picture around what actually is going on in the body when we put this together. Also, together with my research, which I published a year ago. But what it shows is that you'll have this increase in noradrenaline, and you'll have a more focus, you'll have more drive because you also increase dopamine. And dopamine also increases 2.54 above baseline.

Dr. Mark Hyman:
Wow, amazing.

Susanna Soeberg:
Yeah, it's amazing.

Dr. Mark Hyman:
It's like taking a Ritalin basically.

Susanna Soeberg:
Yes.

Dr. Mark Hyman:
Right?

Susanna Soeberg:
It is. Yeah. And I don't know.

Dr. Mark Hyman:
What, you don't take Ritalin?

Susanna Soeberg:
No, I'm saying yes and people are being like, "What?"

Dr. Mark Hyman:
No, from an academic perspective, it's like it's the same mechanism as Ritalin.
We have practice.

Susanna Soeberg:
Or cocaine. Or cocaine. Right?
Yeah, yeah, exactly. And I have also-

Dr. Mark Hyman:
And it's much safer for you. It's much safer for you.

Susanna Soeberg:
It's safer. Yeah. So I think it's amazing that you can go into something this simple, cold water, and you can dip yourself there. You have an increased focus, increased drive, which would give you motivation for the rest of the day to pursue whatever you want to do. And you get a more positive angle to your life even, because you also increase oxytocin, which is also a stress hormone. It's also what we call the love hormone. But it increases your way of viewing your life also. So this is the gratitude that you can feel when you go into the cold water. I don't know if you feel that, but definitely this is what I hear.

Dr. Mark Hyman:
I'm definitely grateful when I get out.

Susanna Soeberg:
Yeah. Exactly. Yeah. But altogether, when you go into the cold water, what it does for you collectively, it widens your window for stress actually. So that is a process when you go into the cold water and you can relax in a situation which is super stressful for you. And you can use this and practice in the, I call it a cold water training sensor for your nervous system, because this is really where you can try and open up this window a bit more so you don't get as easily stressed in your everyday life. I'm not saying that we are not overstressed, but maybe our window for stress has also narrowed. It has narrowed also.
So maybe if we can open that window and we can tolerate be stress a bit better mentally, then we would also not have as much mouth breathing society, which we have today. And when you breathe through your mouth, you activate your sympathetic nervous system, and that's going to also affect your mental health. So it's like you're stressing yourself. It becomes this vicious cycle. So you can use the cold to, you could say, create a better mental balance for yourself, not only just in the moment, because in the moment you will completely forget about your worries because the body goes into a moment of just survival. Even though you did it on purpose, the body's going to react that way. But you can use it, you can use that reaction to complete delete whatever was on your plate. And people worry-

Dr. Mark Hyman:
Oh, it's a great reset. It's an incredible reset.

Susanna Soeberg:
It is. I call it the control, alt, delete effect, because that's exactly what it does.

Dr. Mark Hyman:
Oh my God, that is so good. Control, alt, delete. So you can control, alt, delete all of your stress response and come into a calmer nervous system state that allows you to be more focused, present, happier, increases all the happy mood chemicals, love chemicals. It's really quite remarkable. And it's something that happens pretty quickly.

Susanna Soeberg:
It happens so rapidly, within a few minutes, actually. So if you can stay in the water for just getting over to the other side, I call it, of the cold shock, where you stop hyperventilating and you can relax in the water, you don't really have to stay there much longer. You have already the benefits. Right? So you can go up and what happened there is you completely deleted your worries and you then have a new, you can say mindset. Your brain is full of all these good chemicals and that is going to make you view, your problems, your life, everything nature, people around you, in another perspective because now you have this positive mind, and that's how you go into life. So if you can do this a couple of times a week, imagine how that's going to affect your life if you, on purpose can go out and take this happiness pill, it's just cold water.

Dr. Mark Hyman:
Well, it's like a stress resilience. Right? Think about if you never exercise and you're a couch potato and then to go hike 10 miles, it would be a really hard thing to do. And if you are constantly in a state of stress that is psychological stress, but you don't have a way to reset your nervous system and become adapted to it, you don't develop stress resilience. You can develop exercise resilience where you can be fit and exercise, it doesn't bother you. Whereas if you don't have that, it's going to bother you. Same thing with what you're talking about, it's a way of building stress resilience in our life so we can handle more stresses over time and not be so buffeted around by all the difficult things in our life.

Susanna Soeberg:
Yeah, exactly. And I think one thing that we can point to, which it's very difficult to prove, how do you get more stress resilience with this? But I think one thing we can point to as a kind of proof to this, is that we have found in my study is that you actually get warmer from going into the cold water. So becoming a winter swimmer, coal planter, dipper, whatever we call it, you become a warmer person, meaning that you will be more comfortable in the cold. And I as myself can completely vouch for that because I was definitely a person who was a bit of a, I call myself a cold sissy back then, but today I am not.
Today, I'm completely, I would say I don't fancy the cold and I don't think anybody should actually, that would be really weird. But I like the cold today because know what it can do for me. And a cold wind today doesn't bother me as much as it did when I wasn't going to swimming. So my stress resilience against temperature changes has actually changed. So it doesn't bother me as much anymore. So I think that is one thing that we can point out and say, well, that's just a physical thing. So imagine what is actually also happening in your mind.

Dr. Mark Hyman:
Yeah. And also, what's interesting is a lot of mental health problems are problems of inflammation in the brain. So depression is inflammation in the brain. You touched on it earlier, ADD is inflammation, autism is inflammation, Alzheimer's inflammation in the brain. So a lot of the things that are going on in the brain mood-wise are inflammation, as well as all the other chronic diseases. So can you talk about the role of cold therapy for inflammation in general, and what it does and what the mechanisms of action are and how it works?

Susanna Soeberg:
So now we are going to talk about the brown fat because that is what we activate when we go into the cold water. So the brown fat, I'm just going to repeat a bit because I didn't really say it all. So when you go into the cold water, as I told you, you activate the cold preceptors in the skin and that's going to send a signal to the brain and that's going to release noradrenaline, which is a stress hormone, and that's going to activate our healthy brown fat. And that's located, you can almost touch it actually, it's underneath your clavicle bones. And I measured it in my studies. It's just at one to two millimeters under your skin, so you can almost touch it actually. Yeah, exactly. And that's the largest depot. There are six places in the body where with this... It's actually an organ. You can define it as an organ. It's six places, but it's around the central nervous system. And it makes sense. We have-

Dr. Mark Hyman:
It's on your back, too. Right? Is in between your shoulder blades and your back?

Susanna Soeberg:
Yeah. So down the spine and under your super clavicular bones on your, what is this bone called? The sternum?

Dr. Mark Hyman:
The sternum.

Susanna Soeberg:
Yeah. Sternum bone. Yeah, exactly. And also a little bit around the kidneys and a little bit around the heart, which makes sense. So the purpose of the brown fat is to keep you warm. And this is of course developed during evolution and to keep the human body warm when we were out there and it was super cold and then it was super hot some other times, but back then we had the brown fat to keep us in the perfect regulation all the time. And that takes energy. So the brown fat, when that is activated, it increases our heat in our body, but that takes energy. So that uses glucose and fat from the bloodstream as fuel to activate it and increase our, what's called thermogenesis. But it's also what's called non-shivering thermogenesis, meaning that the muscles are not helping at this point. So what's the-

Dr. Mark Hyman:
Thermogenesis just means heating up the body so you can heat up by shaking and shivering or by the activation of this brown fat that's been there for millions of years.

Susanna Soeberg:
Yes, exactly. Thank you. So it's like the first responder to our body when we get it too cold or we get too hot. But it happens so quick. We have 10 times more cold receptors in the skin that we have for heat, for example. And that is because we can easily die if we fall into cold water. It makes sense that we have been involved in that way.

Dr. Mark Hyman:
That was before climate change.

Susanna Soeberg:
Yeah, exactly. And today we don't get exposed to any temperature changes. So it's live in these houses, 24 degrees all the time. So the brown fat is going to also be activated directly from the skin. So there are studies showing, recent studies actually, showing that there are signals going directly from our skin and directly to the brown fat without passing the brain. So there's like two pathways to activate the brown fat immediately within seconds, as soon as you get a little bit cold on your skin. So also when you just go out in a T-shirt and it's cold.

Dr. Mark Hyman:
Yeah. So that increases your metabolism? That increases your metabolism and actually makes you burn more fat in general? Like you said, the brown fat activation helps burn the white fat, which is what we're trying to get rid of?

Susanna Soeberg:
Yes. And also, it burns your glucose, so your sugar and fat in the bloodstream. So it doesn't only take the fat that is on your thighs and on your belly and you want to get rid of the white fat, but it clears up also the glucose and fat that is already floating in your blood vessels, in your blood streams. Yeah. So it's going to clean up that, and it's going to use from your depots as well if you are cold enough or you can say for long enough and you do, for example, multiple plunges or you also use the sauna. The sauna can do some of these things, too. We need to remember.

Dr. Mark Hyman:
We're going to get there.

Susanna Soeberg:
Yeah, yeah. Exactly. So yeah, that is the first thing that happens with the [inaudible 00:31:15].

Dr. Mark Hyman:
So essentially, what you're saying is that it helps to regulate one of the biggest problems we're facing in society today, which is insulin resistance, which is problems with our blood sugar and metabolism. 93.2% of Americans are in poor metabolic health, which means they're somewhere in the continuum to diabetes. And what you're saying is that this cold therapy can be an adjunct to lifestyle treatments that actually help to improve your blood sugar, your blood pressure, your fat burning, your metabolism. It's just fascinating to me. Right?

Susanna Soeberg:
Yeah. Exactly. That is what happens down the road when you continue this. Yeah. So it actually happens from your first plunge. So it's going to do all this acutely, but eventually-

Dr. Mark Hyman:
Is there data that... Sorry to interrupt, but is there data that show that you can lose weight by doing cold plunges?

Susanna Soeberg:
No, not on the weight scale at least. But we can see in my studies, which we published from Copenhagen University in 2021, that we can increase the brown fat activity and make the brown fat cells more efficient. Because what happens in the brown fat when you continuously expose yourself to the cold is that it increases mitochondria in the cells. And the mitochondrias are the little energy fabrics that you would like more of course, because that's going to keep you young and keep the cells young and it's going to help the brown fat cell increase more heat in your body and that's going to burn more calories from your body as well. So the more mitochondria you can build in your brown fat cells, the more efficient they will be and the more fat and sugar that will burn, and that's going to increase your insulin sensitivity, which we also found in my studies.

Dr. Mark Hyman:
So basically, even though we haven't done the weight loss studies, theoretically, it seems like it actually is increasing your metabolism, which will help you to lose weight and correct the insulin resistance, which will help you even lose weight even more. So it's an incredible positive feedback loop in terms of energy, in terms of mood, in terms of mitochondria, in terms of metabolism, in terms of inflammation. What's the mechanism for reducing inflammation? Because I noticed that if I have pain or stiff or sore, I go into a cold plunge, I come out, it's just gone. It's quite amazing. It's like taking a bottle full of Advil or something.

Susanna Soeberg:
Yeah, it's amazing. And actually, it's really hard to get down to and find the literature, the precise pathway for this and what's actually going on. But what I have found so far is that of course you activate also the IL6. So it is like what you also do when you exercise, for example. And that is an-

Dr. Mark Hyman:
It's inflammatory cytokine.

Susanna Soeberg:
Yeah, exactly. And it's also going to activate IL10. So it's going to do both of course. But because they-

Dr. Mark Hyman:
Anti-inflammatory cytokine.

Susanna Soeberg:
Exactly. And because of that, you are going to lower your inflammation. And when you lower your inflammation and you at the same time increase endorphins in your body, you will have lower pain in your joints or whatever, it could be in your leg or where you have your pain. But it's also because of the more blood circulation that comes to this place where it hurts. And in time when you continue your cold plunging, you will have, can you say cleanup? I don't know, but-

Dr. Mark Hyman:
Yeah.

Susanna Soeberg:
And because of the increase of luekacydes and monocydes, which is going to clean up the inflammation, they will come out and-

Dr. Mark Hyman:
[inaudible 00:35:05].

Susanna Soeberg:
Exactly. And that's going to take that away from your bigger blood circulation. But in the capillaries, there you will have more and more blood circulation and a better vascularity, and that's going to relieve the pain also. So I think there's more processes going on here, which are little bit difficult to come down to say exactly what is going on. I think there is multiple things going on, but some of them could be this.

Dr. Mark Hyman:
So just basically three things. One is, it seems to increase endorphins, which is like morphine or heroin and the pain relief chemicals you have in your body. It increases the activity of a important cytokines. Cytokines or these inflammatory or immune molecules. And one of them is called IL10 that reduces inflammation. And three, it increases initially invasive constriction, which it sort of shuts off blood flow, but then actually the rebound effect is you get vasodilation and then you get increased circulation. So there may be multiple mechanisms to reduce pain.

Susanna Soeberg:
Multiple mechanisms. We can also just mention nitric oxide, I think because nitric oxide, I think it's an important one because when you go into the cold, that happens also in the heat. So we could go back to that. I keep saying that.

Dr. Mark Hyman:
No, we're going to get hot in the soon.

Susanna Soeberg:
But the nitric oxide is going to increase the blood vessel's ability to dilate and contract, and that's going to increase the oxygen delivery to all your cells also in your body. And that is also a good thing for pain relief.

Dr. Mark Hyman:
So nitric oxide is basically, or NO, we did a podcast with Louis Ignaro, who is the one who won the Nobel Prize for discovering this molecule nitric oxide. And you can go back and listen to that and it's so important. It can be so effective for many things. He was even talking about it as a treatment for COVID because of the powerful antiinflammatory effects. And so this is something our body makes through breath, if we breathe through our nose, it's really important to breathe through our nose. If we breathe through our mouth, we don't make nitric oxide. But you're saying is that this cold therapy also will activate nitric oxide, which is a powerful anti-inflammatory compound in our body. It's so important. It's so cool.
All right. So now, we're talking about all the benefits, the brain benefits and mood benefits, the dopamine chemicals, the stress resilience, the increase in our metabolism, the decrease in inflammation, in pain, all these wonderful things. Now, let's talk about, how do we take this drug because it sounds like a miracle drug. What is the best way to do it? What's the amount of time we should do it? What's the temperature we should do it at? And what's the difference between a cold shower, versus a cold bath, versus an ice bath, versus a cryotherapy unit where you can go and stand there? Talk us through all that.

Susanna Soeberg:
Yeah, I can try. It takes a while. It'll take me a while, but okay, so if you use the C or the cold plunge, this is where you can do the same thing. So when you do that, I think it's really important that people do a little bit of breath work before they go into the water because they need to think about their breathing and their nervous system as the steering for how well your cold plunge is going to be. And especially if you are new, this is definitely something you would like to practice before you go into the cold water and you go back totally into panic.
So if you can stand on the jetty or before your plunge and just do some breathing with your nose, so nasal breathing in and out and try to relax. If you're standing in a cold wind, it can be difficult actually. And by that you will lower your stress response. So you activate your parasympathetic nervous system. And if you can do that, you one, rehearse it before you go into the stressful situation where we would like you to continue this. But also, you go into this stressful situation, not already very alert. So that's not really going to help you.
So when you have rehearsed this a bit, and it can take a few seconds and you don't have to stand there for very long, but when you can do that, if you have relaxed a bit, you exhale completely before you step in because that's going to make room in your lungs for doing the first inhalation. And if you are new, and I am especially concerned for the new ones, I want them to have a really good experience. So that's why I'm talking to those people. So if you completely exhale, you make room in your lungs and more capacity, is there right for you to do a inhale and you would do that cause you Yeah, exactly. You activate your gasping reflex. So you cannot really help that, you cannot control it at when it happens at the first time or the second time maybe, but what you can do-

Dr. Mark Hyman:
If you scream when you jump in the cold water, that's okay.

Susanna Soeberg:
It's completely okay. It's completely okay. I think people will forgive you.

Dr. Mark Hyman:
I love that.

Susanna Soeberg:
But what you can do is you can lower your stress. When you go into the cold water and you gasp a bit, just try and remember, just think about your breathing. So the goal is to do completely nasal breathing in and out when you are in the water and also during your cold shock response. But this is not going to happen the first time. I'm just quickly going to say that. But you can try and rehearse it. So if you do a cycling, I think it's fine if people try to keep the insulation through the nose and then out through the mouth. Yeah.

Dr. Mark Hyman:
So how many breaths did you take? The cycling while you're in there? Just do it while you're in the cold plunge.

Susanna Soeberg:
I don't know. I haven't count that. I just-

Dr. Mark Hyman:
And do you want to do it for a minute or two before you jump in? Is that the idea?

Susanna Soeberg:
Oh, you mean on the jetty? I just think you should stand there for, it could be a few seconds or half a minute. It's just until you feel that you have lowered your stress response, especially if you're a little bit anxious about this, try to calm yourself down. This is also a training for your anxiety. Right? It's to open your window for stress. So it also starts before you go into the water. No stress response before you go into the water. But in the water, try and see if you can nasal breathe. But if you can, then just do the cycle of through the nose and out through the mouth and then you can switch. Eventually, when you get more adapted to this, but doesn't have to be the first-

Dr. Mark Hyman:
So breathing before and then breathing when you're in there, and then how long you stay in and what temperature?

Susanna Soeberg:
Oh, yeah. So that depends on where you are. So we in Denmark, in Scandinavia, we have the nature to completely control what temperature we have in the sea. And I think that's amazing because the water temperature is always cold. So we go down to maybe one degree and-

Dr. Mark Hyman:
Celsius?

Susanna Soeberg:
Celsius, in January. But for example, when we start, we call it winter swimming or cold water swimming, we call that from October. And October, that is when the cold water is going to get colder. And that's around, maybe it varies a bit, but maybe it could be 15 or down to nine degrees. And then in November-

Dr. Mark Hyman:
So 15 degrees is in Fahrenheit, about 59, it's 59 degrees Fahrenheit. Right?

Susanna Soeberg:
Fahrenheit. Yeah. Thank you. I'm not good with the converting.

Dr. Mark Hyman:
That's okay. That's okay. [inaudible 00:42:47] everybody gets what this is. There's listeners all over the world, so some are Fahrenheit, some are-

Susanna Soeberg:
Yeah, exactly. I should memorize this actually. I'll try. Yeah. So when you get into the water, it's not that important exactly what temperature it is, as long as it's just cold water. You'll be amazed that actually your metabolism is going to be activated also from 20 degrees Celsius actually. And you don't have to always have the water at one degree. If you can control that in a plunge or something, you can vary the temperature. So just a difference to your skin-

Dr. Mark Hyman:
Well, you said down to nine, nine is 48 degrees, but a lot of these cold plunges go to 40 or something.

Susanna Soeberg:
Yeah. So it doesn't have to be that cold to-

Dr. Mark Hyman:
Really? To have the same benefit. So you don't have to power down to 40 degrees to get the benefit? Do you get more benefit if it's colder?

Susanna Soeberg:
So we haven't done any studies, there are no studies showing the relationship of temperature and activation of the metabolism and what will happen down the road if you have more benefits or if it's going to stress your body too much. We need these studies in the future. But what I'm saying is that for my study where we had winter swimmers in the ocean here, where the temperature from October varied from, I think there is a table in the book actually where I put it in so people can see, what's the temperature in Denmark? What are we talking about? So it's-

Dr. Mark Hyman:
And the book is Winter Swimming for those who want to get it, Winter Swimming.

Susanna Soeberg:
The book is Winter Swimming. It looks like this. It's actually pretty, I think.

Dr. Mark Hyman:
Amazing, amazing.

Susanna Soeberg:
So in the book, there's a table showing from October until the season ends in Denmark, which is in April. So during this time the temperature is going to be from 15 or nine or it varies a bit, and then down to one or zero degrees Celsius. And then it goes up again in February and also in March a bit. And then in May it gets hotter, of course the water, but it's not like it's that hot. 19 degrees Celsius in the summer, it could be a little bit warmer.

Dr. Mark Hyman:
It's still chilly.

Susanna Soeberg:
It's still chilly. And it's going to activate your nervous system. It's going to activate your metabolism.

Dr. Mark Hyman:
So that's interesting. So then cold plunges are 40 degrees. You can go down to 45. My bathtub, I measured the temperature in the winter in my bathtub, I just put cold water on and it's 48 degrees, which is nine Celsius. And so it's pretty cold.

Susanna Soeberg:
It's pretty cold. Yeah.

Dr. Mark Hyman:
And so then you're in there and you could do it in the ocean, which was sort of more adventurous. You can do it in a lake, you can do it in a pond, you can do it in a river, or you can do it in your bathtub in the winter, if you turn on cold water bathtub, just turn on the cold water, you can actually throw bags of ice in there if you want to make it even colder. Or you can buy one of these fancy cold plunges. A friend of mine actually bought a horse trough. It's like where you feed horses water and then it's like a big metal tub. You can buy it for a few bucks at the horse supply store or something. And then he fills it up with water and then throws a bunch of ice in there and it's like how he does it.

Susanna Soeberg:
Oh, wow.

Dr. Mark Hyman:
So there's a lot of ways to do it. How long should you stay in, a minute, 2, 5, 10 minutes? What's the-

Susanna Soeberg:
Post session. Yeah. So I can tell you what we found in my studies that we performed here in Denmark. So in my research study from my PhD, we found that 11 minutes, and this was shown in winter swimmers who had already been swimming for a two to three winter swimming season. So they were adapted. I wanted to study the adapted ones because I wanted to see if that were different from a group of controlled subjects. And I wanted to monitor how much time do they spend in the water. And I wanted to find out with how little can we get away with, because I was not a winter swimmer myself, I was kind of like most comfortable people with temperature, I don't like the cold. So I was thinking, "I'm pretty much like many other people. So can we figure out something that is easy to do but still efficient and efficient enough?" So 11 minutes per week we found and divided on-

Dr. Mark Hyman:
So not 11 minutes all at once, but just 11 minutes per week?

Susanna Soeberg:
11 minutes per week and not at once, divided on two to three days. And also, per day we did, at least in this study, they alternated with cold plunges and the sauna. So it was this contrast therapy where it started with a cold plunge and then they went into the sauna and then the cold plunge again, sauna. And they ended in the cold because I told them that that is how the protocol should be. Because that's good for you. I can tell you why, but it's definitely-

Dr. Mark Hyman:
Yeah, I want to talk about that.

Susanna Soeberg:
Yeah. But just to answer-

Dr. Mark Hyman:
You're talking three to four minutes a time, is what? When you divide 11 by three or four?

Susanna Soeberg:
Three to four minutes per day. So every plunge should not be more than one to two minutes. This is what my subject says.

Dr. Mark Hyman:
Just one to two minutes, not three or four minutes?

Susanna Soeberg:
One to two minutes per dip.

Dr. Mark Hyman:
Oh. 'Cause I put my stopwatch on. I stay in three minutes or four minutes sometimes.

Susanna Soeberg:
Well, do you also alternate with the sauna?

Dr. Mark Hyman:
Yeah. I cheat.

Susanna Soeberg:
No, no you don't. Because my studies show that that's good. That's contrasting. So what you should do, you should plunge for one to two minutes and then you go into the sauna. And my protocol also shows that our winter swimmers stayed in total for 57 minutes in the sauna. So if you divide that also on these days, and if you have of course the facilities you can go and alternate, then you should only stay in the sauna for 10 to 15 minutes and then back in the water and you end on the cold.

Dr. Mark Hyman:
So basically, for about an hour a week, you can have these dramatic health benefits?

Susanna Soeberg:
It's amazing.

Dr. Mark Hyman:
It's dramatic. Now what about a cold shower?

Susanna Soeberg:
Yeah, cold showers.

Dr. Mark Hyman:
Because you Wim Hof talks about a two-minute cold shower in the morning. Is that as good or what's the deal with that?

Susanna Soeberg:
A cold showers are definitely something that I would also say that if people cannot come to a cold plunge, then I think that-

Dr. Mark Hyman:
If you don't have a bathtub or a cold, yeah.

Susanna Soeberg:
[inaudible 00:49:16]. Not all people do. Then I think it's a very good alternative and people can start off in a cold shower. But there are different benefits and I think that if people can only do cold showers, then that is better than nothing. So I would say cold showers are very good for you. It will also activate your brown fat. It will also activate your sympathetic nervous system. You will not have the complete activation of your parasympathetic nervous system. And you will only get adapted to that temperature, which you take your cold showers in. Of course. So there are studies on this showing actually that-

Dr. Mark Hyman:
I was going to say if you live in Arizona and the cold water doesn't get under 60 degrees, well then, but if you live in Massachusetts in the winter, it's 40 degrees.

Susanna Soeberg:
Yes. Exactly. So it really depends on your cold water. How cold is it? So there's this interesting study where they compared temperatures of cold showers, if you can get adapted, the question was can you get adapted to a cold water with cold showers? And they divided these groups up in how long time they ended on cold showers in their hot showers, and there was also a group who just took hot showers. And they found that if you end on a few 10 seconds cold shower with a certain degree, it was 15 degrees and the other group was 12 degrees. And they then put them into cold, cold plunges to see if those subjects who had taken cold showers at 15 degrees Celsius, if they had adapted to cold water just in general. So they tried that out in cold plunges at 10 degrees, but they hyperventilated just as much as the group who didn't take a cold showers. So the temperature is going to dictate whether you get addicted-

Dr. Mark Hyman:
Adapted.

Susanna Soeberg:
Adapted. Yeah.

Dr. Mark Hyman:
I'm kind of addicted to cold and hot therapy actually. I think I might be addicted. It's so addictive. It just makes you feel so good. It's like better than any drug I've ever found. Not that I take a lot of drugs, but it's like it's pretty impressive. The other thing is these cryotherapy units where you go in and you stand, it's 270 degrees below zero. You put a little hat and mittens on and you stand there for three minutes. Does that do the same thing?

Susanna Soeberg:
Yeah. So there's a lot of question. I have a lot of questions around that and I have been through some of the literature. I can't say I've been through it all, but I've definitely been through a lot of it. And I can say that it seems like it can activate your temperature receptors in the skin. So you will have an activation in some degree to your browned at least. And because the temperature is so low, you only spend what, three minutes in there, isn't that right? Like three, four minutes.

Dr. Mark Hyman:
Yeah, yeah, three minutes.

Susanna Soeberg:
Yeah. I think the protocols in the science literature is around the three, four minutes. If that is going to have the same effects as submerging into water, I would doubt. Because the modality is so different. It's different. It's so different. So that is also why if we cannot compare the cold showers with the colds dips, we can also not compare, what do you call it, you call jacuzzi or hot tubs?

Dr. Mark Hyman:
Hot tub. Yeah, with the sauna.

Susanna Soeberg:
Yeah, hot tubs with sauna because it's air and water. More molecules of course in the water, closer to your skin. So it's going to do different things. So we need more studies also on the cryo to exactly say, how is that going to lower your inflammation? But I believe there is something there. I just just need some more backup from the data.

Dr. Mark Hyman:
Yeah, I got it. Well, we're going to link to this study, but in Cell Reports Medicine you published in 2021, a paper called Altered Brown Fat Thermo Regulation Enhanced Cold-Induced Thermogenesis in Young, Healthy Winter Swimming Men. And there you talk about the sweet spot of the dose, right?

Susanna Soeberg:
Yeah.

Dr. Mark Hyman:
And you talk about this concept of why there's a minimum threshold effect, for both cold and heat exposure. So can you talk about what those thresholds are and a little bit more about that study?

Susanna Soeberg:
Yeah, so we already just touched upon the protocol for that. What actually was the results of that?

Dr. Mark Hyman:
That was the minimum threshold was 11 minutes and 57 minutes of hot and 11 minutes of cold. Okay. That's what I thought you were getting at.

Susanna Soeberg:
Per week.

Dr. Mark Hyman:
Per week.

Susanna Soeberg:
Per week, exactly. Yeah.

Dr. Mark Hyman:
Per week. Per week.

Susanna Soeberg:
And divided on multiple days. So-

Dr. Mark Hyman:
I tend to do that in a day if I can. If I can go back and forth for four times and then hot and cold, then I can get that in a day.

Susanna Soeberg:
Yeah. And I think that it could be that we don't know what's the higher threshold because we don't have studies showing exactly on the cold water if that's going to have some detrimental effects on our system down the road. But we do have, yeah, I don't know if we should go there right now, but it's like we have this sauna studies observational studies where we can see a higher and a lower threshold for which a window for where it's definitely good for you.
And that is why, I think because of that it's just stress, heat stress, cold stress. It's just stress for the body. We should keep ourself try to hit the sweet spot in the middle where it's healthy for ourselves and for our system. Because you could be feeling really good when you get out of your cold plunge and some people can build up a long time, which I don't really recommend that people do, even though you can mentally feel, "Okay, I'm getting cooler and cool." I mean, not only physically but, "I'm getting really tough and cool because I can sit in this plunge for a very long time," but-

Dr. Mark Hyman:
Oh my God. Yeah.

Susanna Soeberg:
Yeah. And maybe also some get a little bit competitive around it.

Dr. Mark Hyman:
Yeah, yeah, yeah.

Susanna Soeberg:
I just want to underline that it might be that you cannot really see what's happening right now and you may feel really good afterwards, but it doesn't mean that it's not overstressing yourselves. And maybe down the road it adds up and gets too much. We don't know that, but we need to figure that out and do more stories on it. But I think it's very important.

Dr. Mark Hyman:
Yeah, I agree. I think it's going back and forth. Interesting. But I went to a conference up in the mountains in Colorado and they had a sauna that was amazing. A wood-fired sauna, got super hot and then they had a cold plunge outside, which was really cold. And so we had a group of us for all these overachievers and entrepreneurs. And so we were going back and forth and increasing the time and time and I got to five minutes in the cold, which was pretty damn cold. This one woman got to I think 10 minutes. It was just impressive. It was very impressive. She was like a Navy SEAL.

Susanna Soeberg:
Oh, okay. Yeah.

Dr. Mark Hyman:
No, she wasn't a Navy SEAL, but it was like was being a Navy SEAL, so that's really amazing. Now, I now want to go into the heat part. So we did the cold, you did a good job on the cold. At a high level, is it better you think to do hot and cold alternating therapies? Or is it good enough to do cold or just do hot or what are the advantages to doing both?

Susanna Soeberg:
I would say anything is good. So if you only can only do the cold, then do that. If you can do the heat, then do that. Just do some of it. If you cannot do both. But if you can do both, I would say it's a really good thing to try and contrast it. I can't say what exactly effects you will miss out on because my study shows the combination. Yeah, exactly. But we know what happens in the cold and we know that it creates this hormetic stress and you increase these stress proteins and it repairs the cells, which also happens in the heat. The mitochondria in the cold will increase, and in the heat, the heat will make the mitochondria more efficient. So there are all overlapping effects of doing the cold stress and the heat stress for your cells. And when I talk about cells, you should just think about your whole body because the whole body is building blocks of all your cells putting together. So it is just not one cell I'm talking about, it's the whole organism.

Dr. Mark Hyman:
So it's good to do both, based on what your studies. Can you take us through the mechanisms of action of how heat stress benefits the body? What are the mechanisms and how does it work? Because in my book, Young Forever, I talk about hormesis and I talk about how in this Finnish study, you saw a 40 plus reduction percent in mortality in the group that did four to five saunas a week. And the control grip was like one sauna a week because pretty much everybody in Finland has a sauna. So they all do saunas. So the control group was also doing sauna, but it was still a pretty dramatic reduction. So tell us about how does this work? What's the mechanism of action? What are they doing to the body?

Susanna Soeberg:
Yeah, and I just want to say I think these results are remarkable from Finland. And the study that you mentioned from 2015 is really showing what happens down the road. So this is results after following these sauna bathers for 25 years, and the control group was actually also using the sauna. So one of the things that we in research sometimes debate a lot, is that the control group is a completely other group who doesn't do anything healthy like the sauna bathers or the winter swimmers. But this group has actually chosen to also do this kind of healthy thing. So even though they maybe not have the time to do four to seven times a week or for some other reason don't do that, but they still just do one time. And that's at least a choice in your life that you want to expose yourself to extreme temperatures. So I think it's a good study. I really love it.

Dr. Mark Hyman:
Yeah. So tell us about the mechanism factor. How does the heat stress work to activate longevity switches in the body and healing responses?

Susanna Soeberg:
Yeah, yeah. I'm not sure I can explain all of the things that's going on because I also know from the literature that there are still things that we don't know, but what we do know is that when we activate our heat receptors in our skin, like the the cold receptors that will be sent a signal to the hypothalamus and we will have an increase in noradrenaline. And we will also have an increase of all our stress response, of course. Nitric oxide will also be released and that will be an increase, or the blood vessels would dilate because you need to get rid of your heat in your body.
The brown fat will also be activated. It seems that there are actually studies showing that the brown fat, which is increasing our metabolism, is also activated in the heat. It's kind of counterintuitive. I know that. But I have tried this in India, on Sri Lanka actually. So when you get really, really hot and you are too hot, then you are given a tea to drink some tea. And that's like, "Why are you giving me something really hot when I am too hot already?" But that is to drink that get warmer in your core. And when you do that, you will help your blood vessel to open and that makes your body a body's ability to sweat even better.
So that is what the brown fat also does in your body, it activates. So you will open your blood vessels, you can get rid of the heat, but the heat stress response, the best response from that, is actually an increase in sweating and your ability to sweat, but also a lower cold temperature. So for every time you go and expose your heat, you activate your heat stress response in your body, you will prepare your body for the next time. And by that, the body is sensing, "Okay, I will have to prepare myself." So your core temperature actually by the time lowers a bit and you can use that for something. And I don't know if you want to know that, but?

Dr. Mark Hyman:
Yeah, of course. Now what, use it for what?

Susanna Soeberg:
Yeah, so I love that people, "What could we use a lower core temperature for?" And I'm also like, well, actually, when you lower your core temperature, you have a higher window for, for example, when you go and train in the training center when you do your sport, because what happens is what is lowering your running economy is actually that your temperature goes up. So if you want to have a higher training economy or you can train for a longer time before you get exhausted, before you hyperventilate and you have to stop, that is your temperature going up. So if you can widen that window a bit, then you are actually getting fitter.

Dr. Mark Hyman:
Oh, wow. So it makes you fitter? It actually, I think the science is there, it increases your cardiovascular fitness.

Susanna Soeberg:
It is cardiovascular fitness. And this is also shown in studies that because of the dilation and the contraction of the cells, of the blood vessels, but also because of the sweating, that decreases your ability to sweat. That is going to, for your blood vessels, for your whole circulation, is like a training, it's like training out or it's like a moderate HIIT training, I would say.

Dr. Mark Hyman:
Yeah, yeah. Interesting. So it's exercising by sitting in a sauna?

Susanna Soeberg:
Exactly, yeah.

Dr. Mark Hyman:
Essentially. And what is interesting, it has really great cardiovascular benefits. Tell us about the cardiovascular benefits of sauna.

Susanna Soeberg:
Yeah, so going back to the studies that we just talked about before, the observational studies from Finland, which shows that if you go into the sauna two to three times per week, it will lower your risk of cardiovascular disease by 27%. And if you go into the sauna four to seven times per week, which is almost like one time every day, then you can lower your risk for cardiovascular diseases by 50%. So I think that there is a lot of health benefits, which we can see here in this study on the long-term, which is then, and now I'll go back to that, because of lower inflammation, because the heat stress is going to activate your system, your blood vessel will dilate, and you will have an increased ability to also contract and dilate your blood vessels.

Dr. Mark Hyman:
Well, I think just to talk about the cardiovascular fitness benefits in terms of blood pressure, heart rate variability, autonomic nervous system health, stress resilience, reduction in congestive heart failure complications. It's really quite interesting to see the data on this. Right?

Susanna Soeberg:
Yeah. Exactly. So the cardiovascular health increases because it's like a cardiovascular fitness you do when you go into the heat. So your blood pressure will actually be lowered. There are studies showing that the blood pressure goes down when you exercise your system in the heat and also your heart rate and your heart rate variability. So there are really signs now today backing up that the heat stress is a workout for your body.

Dr. Mark Hyman:
So just to unpack it a little bit for people. So heart rate variability is a metric that is measuring the complexity of your heart rate, the more complex it is, the healthier you are. And it's a great sign of your stress response, your autonomic nervous system. And it's sort of a great measurement that we can use and we can do it through our Oura Ring, Apple Watch, all kinds of garment Fitbit. We all measure this heart rate variability, which is really an important thing to track because it's really the sign of your overall health, and it correlates with mortality and many other things. And so what we see with saunas, it actually increases the complexity and increases the heart rate variability, which is really an important effect of the saunas and the heat therapy. There's another thing that happens, it has to with heat shock proteins. Are you familiar with the heat shock proteins? Can you talk about what are heat shock proteins, why they matter and what they do, and why it's so important for us to activate these heat shock proteins in our body?

Susanna Soeberg:
So heat shock proteins increase when you go into the heat and the body sense that now you are getting warm. So the heat shock proteins are in all your cells and you can increase that when we get warm or the cells get warm. And that is to protect the cells. So the heat shock proteins increase and they repair the cells from the inside. Meaning that if you don't overdo it, the heat shock proteins is going to repair the cells so they will live longer. So that's good for longevity. So if your cells live longer, you will also live longer. So the heat shock proteins, there are many of those. There is especially one family of those, it's called heat shock proteins 70, which is the most studied I have found to show that when you activate that with heat, then this group of heat shock proteins is going to repair the cells. That was also the FOXO3, which I don't know pronounce that right, but FOXO3.,

Dr. Mark Hyman:
FOXO3, it's a mitochondrial regulator. Right? It relates to longevity.

Susanna Soeberg:
Yes, exactly. And that is also increasing in the heat and that's going to help your cells also be repaired and it's going to live longer and as long as you don't overdo it, that's back to the hormetic stress, the healthy stress, that if you overdo it, then that will just exhaust-

Dr. Mark Hyman:
Yeah, you'll get heat shock and you die or you go too cold, you get hypothermia and you die. Right? So it's that goldilocks amount, right, what you're talking about.

Susanna Soeberg:
Yeah. I think the overstressing will help start before you die.

Dr. Mark Hyman:
That's right. So this is amazing. So heat shock proteins are important. Also, they help with protein repair, don't they? A lot of proteins are damaged. And then one of the hallmarks of aging that we talk about, and I explain in my book, the hallmarks of aging is damage to proteins and those damaged proteins don't work properly. And proteins are like the messenger systems in our body, they do so much and build tissue or repair organs, but they're also communication systems. And so a lot of the communications get screwed up. And we have an information problem, almost like bad software that's running your biology. And so these sauna therapies seem to improve these proteins and fix them and repair them. Is that accurate?

Susanna Soeberg:
Yeah. Exactly. The heat shock proteins repair the proteins in the cells, which is a little magic doctor in our cells that you can just call with just going into the heat. And I think it's very simple and you don't have to be really good at it or anything. You don't have to be in one special, you just go into the heat and then you could just repair yourself just for a bit, just for a little bit of dose of repairing myself, and then you can go home. You don't have to overdo it even.

Dr. Mark Hyman:
Yeah, and it's anti-inflammatory also, as you mentioned, and the FOXO is involved in regulating inflammation in the body, so it helps with that. But also, it seems to activate the innate immune system. Our immune system gets boosted when we do this hot therapy.

Susanna Soeberg:
Yeah, it seems also to be activated. So-

Dr. Mark Hyman:
What amount of saunas do we need? You mentioned 57 minutes a week. Is that a reasonable amount? That's four 15 minute sessions a week?

Susanna Soeberg:
Yeah, so I'll try to compare this actually with the Finnish sauna studies just to see if it's comparable in what's we can maybe call a good window for stress. So if we do the 57 minutes over a week, divided on two to three days and with two sessions each day, that means you could do four session each week or you could do six sessions each week. So it's between 10 and 15 minutes each session then. Okay? Hope you follow.

Dr. Mark Hyman:
Yeah, yeah, yeah, yeah. See, I try to get so hot that I can't stand it and then I go on and get so cold that I can't stand it and then I just get out. So it's like I go back and forth. But you're saying you don't even need to do it that extreme, just a little bit even makes a big difference.

Susanna Soeberg:
Exactly. I can come with a good example after this. I can tell you how little you can do actually.

Dr. Mark Hyman:
So that's not so scary then for people. It's like you don't have to be The Iceman and be Wim Hof in the ice bucket for two hours and get the benefit. Right?

Susanna Soeberg:
No, you can be completely normal, scared of the cold and hate the heat and just say to yourself, well, I'm not really loving running 10 kilometers either. That's not really something I personally love to do, but I do it and I go up and train. I like that now. But in the beginning-

Dr. Mark Hyman:
You didn't like it. Yeah.

Susanna Soeberg:
No. And everybody who takes a break from exercise don't love the first run for five kilometers and they will hurt in your muscles. And that is just exactly when you do the hormetic stress by going into the cold and through the heat. But back to the 57 minutes. So you can divide that out. And if we compare it with the Finnish sauna studies, it seems that there's a higher and a lower threshold as well.
But we see that if you do more than 19 minutes, up to 30 minutes, so 19 to 30 minutes, it seems also to have... Right, I'll start another place. So I'll say from zero minutes and up to 19 minutes, you will have an increase, you'll have a lower risk, sorry, a lower risk of cardiovascular diseases, and that window will continue up to 30 minutes, but it won't be better or anything, your risk will get better. But after 30 minutes, there seem to be a plateau where the benefits are not shown anymore. And maybe even the risk of cardiovascular diseases increases. So it seems that under 30 minutes is like the healthy and if you can stop at 19 minutes, that is where you get the most out of it. So my protocol shows 10 to 15 minutes, even gives you benefits. So that is in between, so that's why I call it a bit maybe it's the sweet spot. I don't know.

Dr. Mark Hyman:
Love that. I love that. Well, I also emphasize important people stay hydrated, so make sure they drink plenty water. And also I recommend electrolytes because you lose a lot of electrolytes and people will often be able to tolerate more heat if they stay hydrated and have electrolytes. So that's a little tip. So in terms of technology, there's infrared saunas, there's regular heat saunas, there's hot baths, there's sauna blankets. Are they all the same? What's your better? Does it make a difference? Do you have any data? Do we not know?

Susanna Soeberg:
Yeah, there are not too many, I don't want to offend anyone, but there are not very good studies on this yet, but there are some studies and it shows that you can use the infrared sauna and it's going to... The most studies are on skin on eczema. And if it has a difference in eczema, patients in children, and also in adults, and it seems actually to increase the moist of the skin. And if you don't overdo it, you won't get burned. That was also one of the results for-

Dr. Mark Hyman:
For infrared?

Susanna Soeberg:
For infrared, yeah, you can burn yourself actually from that. But I think it's a difficult thing to go into infrared sauna research because there are different length of the sauna-

Dr. Mark Hyman:
Waves lengths.

Susanna Soeberg:
Exactly. And there are the short, the mid, and the long length of wavelengths. So it's very difficult to compare also these studies. So some saunas have only the long wavelengths and some have the near combined with... It's a little bit difficult to go into that and-

Dr. Mark Hyman:
We need more data, but they work.

Susanna Soeberg:
They work.

Dr. Mark Hyman:
They work. And what about hot bath? Because many people don't own a sauna. Yeah. What about a hot bath? Does that work?

Susanna Soeberg:
Yeah, hot baths are very good, actually, it seems. So there are more studies on this, and I can just give an example.

Dr. Mark Hyman:
So it should be as hot as you can handle it or it shouldn't matter?

Susanna Soeberg:
No, no, no, no, it shouldn't be. So there are studies in where they have tested type two diabetic patients and looked at glucose levels where they have been in a hot bath. They used the hot bath for three weeks, and they saw that the type two diabetic patients who was in the study, they actually lowered their HB1C level.

Dr. Mark Hyman:
Wow.

Susanna Soeberg:
Which is, yeah-

Dr. Mark Hyman:
Your average blood sugar. Yeah.

Susanna Soeberg:
It shows the amount of how much sugar over a period of time they have in the blood. And there are also studies showing that is the temperature was 39 to 40 degrees Celsius. What is that Fahrenheit?

Dr. Mark Hyman:
Like 100. They're 90s to 100. Yeah.

Susanna Soeberg:
Okay. So you can use that. Right?

Dr. Mark Hyman:
But baths can be effective, but they're different than saunas and we don't know if they activate all the same pathways or do they?

Susanna Soeberg:
Not the same. But it's also the diving response because you also go into the hot water, but it seems that it also activates the brown fat, but that is not tested like my study exactly what they have measured, what happens if they're hot bath, but you activate your metabolism as well, and you must do that because they also lower that blood pressure, heart rate and also the blood sugar. But the other study about the pain showed that you can have a pain relief if you go into a hot bath at 20 degrees Celsius, which is on the middle side. Not too cold, but not too hot, but it's like, yeah. And also, another study showed 25 to 27 degrees also had pain relief effects. So you can have many, many different temperatures doing all this. So I just think that it also shows that you should vary the temperature, and even the temperature just being different from your skin is going to activate-

Dr. Mark Hyman:
It makes a difference. So basically, you don't have to live by the North Sea in the winter to do this. Right? You can use a cold shower and a hot bath, and most people have access to that. You can do cold showers, you can alternate back and forth. You can do them independently. This is all stuff that we most people have access to. But you think it's worth the investment to buy some type of sauna, a sauna blanket, a small sauna for your house, or a cold plunge?

Susanna Soeberg:
Yeah, I think so. If you are a person-

Dr. Mark Hyman:
If we look at all the things we spend our money on for our health, it's the gift that keeps on giving. I put a steam shower in my bathroom.

Susanna Soeberg:
Really?

Dr. Mark Hyman:
23 years ago. And it's still working. I've had to replace the glass a little bit around the shower. But basically, it's the gift that keeps on giving. And I just have a big bathtub and I fill it with cold water. I don't cold lunge yet, but it's something I've been doing for so long, and I find it one of the most powerful health enhancing technologies out there. And it's basically very inexpensive or can be close to free.

Susanna Soeberg:
It can be almost free. But actually, I think people should start thinking about this like, for example, exercising and going to the gym or buying your exercise equipment. You have to exercise your nervous system also, and you have to buy some equipment for this because this is training your physiology, but also your mental health. So this is doing a lot more, I think. Of course, the exercise is actually doing some of the same things, but here you can do it really rapidly and you can mix this, but you have to invest in it, and people just have to get used to the thought of exercising your nervous system, I think.

Dr. Mark Hyman:
Well, this is so exciting because there's all these people talking about biohacking this and biohacking that, but you're a PhD research scientist, and you spent your career focusing on the biology of hot and cold stress and how that can activate our body's own innate healing systems and even activate our longevity pathways, which I think is just phenomenal. And what's great about your work is that not only are you publishing papers in academic journals, but you create an online school for people called the Soberg Institute, which is not how you pronounce it in Danish, but for us who don't speak Danish. So Soberg is how I pronounce it, S-O-B-E-R-G Institute. And it basically teaches you how to use heat and cold therapy and breathing in a way to optimize your health. And you've written a book called Winter Swimming, the Nordic Way toward a Healthier and Happier Life. It's super exciting. So give us just briefly, a couple of minute rundown on the institute, what we're going to learn and why people should sign up right now.

Susanna Soeberg:
Yeah. Well, I made the school because I get so many questions about how to do this, and I would really love to teach everyone about this, like I did my subjects in my studies. So I have made this course. It's a free week course, a 21 days. It's just something that you can do in your own pace, but it's about the cold, how to use the cold in different ways, but also the heat, and how functional breathing is also going to lower your stress level. So the main thing about the course is how to lower stress and inflammation to a more healthier and happier life. So I give you a rundown through all these videos. It's all video content, which you can take in your own pace, and it's very bite size. So every video is very short, but there are many of them in a library. So it's really easy to go through. And I'm very happy that I just got the first reviews of my courses and they are actually brilliant. So I'm really happy. I'm really happy.

Dr. Mark Hyman:
Congratulations.

Susanna Soeberg:
I spent so much time on this course, so I'm happy it's well received so far.

Dr. Mark Hyman:
What's so great is that a lot of academic researchers don't translate their work into practical applications for people. And I'm so happy you created the institute. I'm so happy people can go online and find it. We're going to put the link in the show notes, but you can just Google the Soberg Institute, S-O-B-E-R-G. You can also get her book, Winter Swimming. And also, if you go get the course now, you get a 10% discount on the three-week online thermals course with the code Hyman, H-Y-M-A-N. So I would encourage you to check that out. We'll put all this in the show notes, and I encourage you all to make sure you incorporate heat and cold therapy into your life on a regular, weekly basis. It's a game changer in so many ways. It'll make you happier, healthier, fitter, skinnier, and live a long time. So I think it's kind of a win-win.

Susanna Soeberg:
Yeah. Amen.

Dr. Mark Hyman:
Well, Susanna, thank you so much for your work. Keep going at it. We want to learn more research from you over time. Everybody listening to this podcast, I hope you liked it. It certainly was exciting for me to learn so much about the science behind the things that I've known feel good, and now we know why. So thank you so much Susanna. And for those listening, if you've actually had experience with hot and Cold Therapies, what have they done for you? How have they changed your life? We'd love to hear or leave a comment, share this with your friends and family, everybody needs to hear about it. And subscribe wherever you get your podcast and we'll see you next week on The Doctor's Farmacy.

Susanna Soeberg:
Thank you for having me.
Closing:
Hi everyone. I hope you enjoyed this week's episode. Just a reminder that this podcast is for educational purposes only. This podcast is not a substitute for professional care by a doctor or other qualified medical professional. This podcast is provided on the understanding that it does not constitute medical or other professional advice or services. If you're looking for help in your journey, seek out a qualified medical practitioner. If you're looking for a functional medicine practitioner, you can visit ifm.org and search their Find a Practitioner database. It's important that you have someone in your corner who's trained, who's a licensed healthcare practitioner, and can help you make changes, especially when it comes to your health.