AMA #7: Cold Exposure, Maximizing REM Sleep & My Next Scientific Studies

Andrew Huberman (0:00)

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 is an Ask Me Anything episode, or AMA. This is part of our premium subscriber channel. Our premium subscriber channel was started in order to provide support for this standard Huberman Lab podcast, which comes out every Monday and is available at zero cost to everybody on all standard feeds, YouTube, Apple, Spotify and elsewhere. We also started the premium channel as a way to generate support for exciting research being done at Stanford and elsewhere. Research on human beings that leads to important discoveries that assist mental health, physical health and performance. I'm also pleased to inform you that for every dollar the Huberman Lab premium channel generates for research studies, the Tiny Foundation has agreed to match that amount. So now we are able to double the total amount of funding given to studies of mental health, physical health and human performance. If you'd like to subscribe to the Huberman Lab podcast premium channel, please go to hubermanlab.com/premium.

It is $10 a month to subscribe or you can pay $100 all at once to get an entire 12 month subscription for a year. We also have a lifetime subscription model that is a one-time payment. And again, you can find that option at hubermanlab.com/premium. For those of you that are already subscribers to the premium channel, please go to hubermanlab.com/premium and download the premium subscription feed. And for those of you that are not Huberman Lab podcast premium subscribers, you can still hear the first 20 minutes of today's episode and determine whether or not becoming a premium subscriber is for you. Without further ado, let's get to answering your questions. The first question asks, is it possible to get a cold or to get sick from deliberate cold exposure? And I suppose a related question is, should you even do deliberate cold exposure if you have a sniffle, a cold or a flu? I get that question all the time as well. So I'll answer both of those questions and I will also touch on some of the immune enhancing effects of deliberate cold exposure. But just to make sure that we answer the specific question asked here right off the bat, is it possible to get a cold or to get sick from deliberate cold exposure? Well, assuming that you're not doing the deliberate cold exposure for more than say, five or six minutes at one stretch, probably not directly from the deliberate cold exposure. I mentioned that because most people are doing anywhere from about a minute to three minutes, sometimes five or six minutes. And maybe for those of you that are really pushing it, 10 minutes of deliberate cold exposure. And most often after doing that deliberate cold exposure, people are either getting clothed or they're getting into a sauna or they're taking a hot shower and then getting clothed and heading off into their day or off to sleep, depending on what time of day or night you happen to do your deliberate cold exposure. We can safely say that if you warm up after a relatively brief, meaning one minute to, let's extend it out to 10 minutes, 10 minute deliberate cold exposure. Although I really want to caution people to not do 10 minute deliberate cold exposure right off the bat. If you are somebody who is not accustomed to it, don't jump right up to that long exposure to cold water. Start with shorter exposures. But if you're doing that one to 10 minute deliberate cold exposure and then you're getting warm afterwards and heading about your day, I can't see how the deliberate cold exposure itself would enhance your susceptibility to getting sick. That said, we know from an enormous number of studies that have looked at cold virus transmission and other forms of viral and bacterial transmission, that the environment that you happen to be in does impact your susceptibility to colds and other types of viruses and to bacterial infections in the following way. There have been controlled studies in which people go into laboratories, whose laboratories have rooms which they can very tightly control the humidity, so essentially the water content in the air, as well as the temperature in the room. And if you look at the total mass of those data, we can say a couple of specific things in kind of bullet point fashion. First off, cold dry air does seem to increase our susceptibility to viral and bacterial infections because whether or not you're a mouth breather or a nose breather, and by the way, I suggest everyone be a nose breather unless you're exercising hard enough that you have to breathe through your mouth or you're talking or something of that sort. But if you're a nose breather or a mouth breather or both, viruses and bacteria enter through your nose and mouth, sometimes through your eyes, but your nose and mouth are going to be the main sites of entry and your main barriers to viral and bacterial infections. In fact, one of the ways you are constantly fighting off bacterial and viral infections that you're exposed to all the time is by way of those viruses and bacteria getting trapped in the mucus lining of your nose or your mouth, most notably in the back of your throat. So if you spend time in cold, dry environments, there is a tendency for that mucosal lining to be thinner. There is a tendency for that mucosal lining to not be as robust in general. When I say robust, what I mean is that if you're mouth breathing, for instance, in a cold, dry environment, I'm thinking from the time I spent in Cambridge, Massachusetts in winter at the tea station, you know, if you're, I'm just imagining myself, because it was so darn cold back there, you know, breathing through your mouth or having gone for a run and your mouth isn't covered, or even if you're deliberately nasal breathing, you're drying out your nasal passages and making them more susceptible to infections. Does that necessarily mean that every time you go out in cold, dry air that you're going to get an infection? No, of course it doesn't. But to relate this back to the question we had before, there are a lot of data pointing to the fact that more humid, warm environments are going to make your mucosal lining and the general upper respiratory area more, I don't want to say immune because I don't want to conflate that word with the other meaning of immune, it's going to make it more robust against bacterial and viral infections. Okay, so if you get into a cold shower or a cold plunge or a cold ocean or a cold lake and then you get out and you're out there shivering and shaking, trying to boost your metabolism or whatever it is that you're doing it for and it's cold, dry air and especially if you're mouth breathing in that cold, dry air, yes, I could see how that might lead to a higher probability of getting a cold or other type of infection, but there's nothing specific about the deliberate cold exposure, itself that can induce a cold or other type of infection, assuming that the water is clean, right? We're not talking about bacterial infections of cuts on the skin, etc. We're talking about colds and other forms of being sick, namely upper respiratory infections, right? Now, with that said, I often get asked whether or not for people who already have a little sniffle, they're feeling a little rundown or perhaps a lot rundown should they do deliberate cold exposure. And what's a little tricky to give a one size fits all answer, but I think we can safely say that if you are feeling malaise, if you're feeling like you have to rest, you're tired, you're not feeling good because of a cold or because of a flu or because of a bacterial infection. Okay, now I'm not saying just feeling not good. I'm saying feeling not good due to a cold or other form of virus or bacterial infection. Then I would say stay out of deliberate cold exposure. Don't use it. Now, why would I say that? Given the data I'll talk about in a few minutes, showing that regular deliberate cold exposure, if done correctly, can in fact increase immune system markers and perhaps even make you much more robust to combating different types of infection through the release of adrenaline. We'll talk about what all that looks like in a moment in terms of protocols and some of the science. But to just be very clear and very direct, if you're sick, stay out of deliberate cold exposure. There I would instead recommend warmer hot baths, warmer hot showers, the sauna, et cetera. But I also would caution that if you are getting into saunas that are too hot, saunas that are so hot that it's stressful for you. And again, a lot of people use deliberate heat exposure because of the stress it induces. They're doing some heat-induced, for instance, heat shock proteins and different ways of increasing heart rate. That's a different sort of thing. That's hard, it's stressful in order to generate an adaptation. I don't recommend doing that. In fact, I don't recommend doing deliberate cold exposure, exercise or deliberate heat exposure if you're feeling really not well. Now, if you're feeling just a little bit not well, you're feeling a little bit rundown, a little bit of sniffle, a little bit of malaise. Well, then it's kind of an edge case where we could say, all right, you know what? Just take a hot shower and go to sleep. That's probably the best advice, right? That good old fashioned advice. But if you are determined to do your deliberate cold exposure anyway, then I would say definitely get warm or take a hot shower afterwards, hot bath or a hot sauna, but not too hot that it's stressful, of course. And keep in mind that one of the variables that's been measured quite a lot in laboratory studies of deliberate cold exposure is the increase in immune system markers. So I'll provide a few links to some of these studies, although nowadays there are many, many of them, but it's very clear that deliberate cold exposure can increase the release and the production of different immune molecules and immune cells. One slightly older study, but nonetheless, a good study that has relevance here is entitled Immune System of Cold Exposed and Cold Adapted Humans. Now keep in mind that this study is a little bit extreme and there are reasons for that, I guess to make a long story short, oftentimes in order to quote unquote see an effect in a study, scientists will use conditions that are pretty extreme compared to control group. Oftentimes you'll see a dose response too, but it's a little bit trickier to do with human studies of deliberate cold exposure. It can be done, but not too common. But here they used a pretty, what I would call extreme stimulus. It was exposing people to 14 degrees Celsius water. So that's 57.2 degrees Fahrenheit, which isn't that cold. It's like cool, I would say very cool water, but not what you might consider cold, depending on how well you tolerate cold. And that will vary, of course. But they had people exposed to that for an hour, which is a pretty long time. Most people, as I mentioned, are using colder temperatures of deliberate cold exposure. So even high 30s, low 40s, maybe upper 40s, for anywhere from one to 10 minutes, depending on how conditioned they are. And again, don't just jump into 10 minutes of deliberate cold exposure. Or please, at 35 degrees or 40 degrees or even 45 degrees, if you aren't familiar with deliberate cold exposure, you have to ease into these sorts of things over time. And if you're interested in protocols for deliberate cold exposure, we have a zero cost newsletter at hubermanlab.com. Go to the menu, go to newsletter and you can find that. We've done several episodes on deliberate cold exposure. In any event, this study, immune system of cold exposing cold adapted humans, as I mentioned, had people in 14 degrees Celsius water for one hour. And basically what they found is that one exposure to cold did not change immune system function in any kind of significant way. However, what they found was if people did deliberate cold exposure repeatedly over a period of about six weeks, and by repeatedly, I mean three times per week, what they found were trends. And again, trends are not statistically significant, but trends towards increases in plasma concentrations of things like IL-6, interleukin-6, or total numbers of T lymphocytes and T helper cells and T suppressor cells and activated T and B lymphocytes. These are all immune cells and immune molecules that roughly correspond to an increase in immune system function. If you'd like to learn more about the immune system, I did an episode on immune system function. Again, you can find that at hubermanlab.com, and it spells out the basic cell types of what's called the innate and the adaptive immune system. This study, which we will link to in the show note captions, is but one study of several other studies showing that deliberate cold exposure can increase immune system markers, especially when deliberate cold exposure is done repeatedly over time. So in this case, three times a week over a period of six weeks. But again, I want to highlight these aren't highly significant effects. These are trends in the direction of increased numbers of immune cells and immune markers. Now, what's impossible to know is how those trends translate to actual resistance to specific concentrations of say cold virus or flu virus or any other virus or bacteria. That would be great, but that's a very difficult study to do, especially in the context of deliberate cold exposure as well. Now, we can all be scientists about this and say, what is it about deliberate cold exposure that would increase immune system function? And there we can confidently say the molecules epinephrine and norepinephrine, which are released in both brain and body in response to cold water exposure, as well as things like deliberate hyperventilation. The release of norepinephrine and epinephrine into the brain and body is known to have a number of different effects related to the immune system. It can be proimmune, at least in the short term. And in the long term, meaning if norepinephrine and adrenaline, again, those are just different names for norepinephrine and epinephrine. I'm sorry those are the same thing, but that's why I use them interchangeably so that you don't get confused if you see norepinephrine or norepinephrine. That's the same thing. You hear epinephrine or adrenaline, same thing. Deliberate cold exposure or deliberate hyperventilation will increase those molecules, norepinephrine and epinephrine, and their increase is proimmune. It can trigger the activation of immune cells and immune molecules that can make you more resistant to certain forms of infection. However, if norepinephrine and epinephrine are elevated chronically, and especially if they are elevated late in the day, repeatedly over many, many days, that can cause reductions in the number and efficiency of immune cells in combating infections. So getting cold in this context of whether or not you can get sick from it should really be considered more as what happens when you spike your adrenaline and norepinephrine. And there's one other study that we can look to, which is now really a famous study published in Proceedings of the National Academy of Sciences, looking at so-called Wim Hof breathing. But really that just translates to cyclic hyperventilation. So this is inhaling through the nose, exhaling through the mouth repeatedly, 25 times or so.