November 30, 2023

AMA #13: Winter Months & Sickness, Wim Hof Breathing & Stressors

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In the full AMA episode, we discuss:

  • Wim Hof Breathing and Sickness
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ANDREW HUBERMAN: Welcome to the Huberman Lab podcast, where we discuss science and science-based tools for everyday life.


I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. Today 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 the 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. So without further ado, let's get to answering your questions.

The first question is about colds and flus. And the question specifically is, why is it that we get more colds and flus in the winter months? Is it the temperature outside? Is it the fact that people are spending more time indoors? Or is it a myth that we get more colds and flus in the winter months?

Well, the first thing is that the research very clearly shows that in winter months, there is a greater prevalence of colds and flus. Now of course, the words, in the winter months, means many things. For instance, in most areas of the world, unless you live directly near the equator, in the winter months means that days are going to be shorter and nights are longer than in the summer months. In general, that's true.

It's of course, especially true if you live very far from the equator. So imagine somebody living up in Tromsø Norway, which is very close to the North Pole. In winter, days are very, very short in Tromsø. And conversely, in the summer months, days are very, very long in Tromsø, Norway. Now, Tromsø, Norway represents an extreme of day length variation according to time of year. The closer you get to the equator, the less variation there is in day length and therefore night length across the year.

However, in most locations on Earth, days will be significantly shorter by about an hour or two at least for certain parts of the year. And in general, shorter days correlate with colder temperatures. That's what's really important to know, which is that shorter days generally correlate with colder temperatures regardless of where you live on the planet Earth.

So in the winter months, as we're calling it, involves at least two things, shorter days, which means what? It means less sunlight and either more artificial light or more darkness, depending on how much artificial light you rely on. It also means, as we mentioned, colder temperatures. Colder temperatures, of course, doesn't necessarily mean that you are exposed to those colder temperatures because what's the third thing? Shorter days and colder temperatures outside mean that people are spending more time indoors.

So what the research clearly shows is that one of the reasons, not the only, but one of the reasons for the greater prevalence of colds and flus in the short days, a.k.a. winter months of the year, is that people are spending more time indoors and therefore at closer proximity. Which raises a whole bunch of really interesting questions that have been explored in the peer reviewed research about proximity cold and flu transmission.

There have been studies, for instance, where people come into the laboratory who are suffering from cold and flu and are sneezing. Having them sneeze at different proximity to other people. Obviously, people are doing this under consent. They're agreeing to participate in these particular experiments.

And there does seem to be a very nice relationship between physical distance between you, the uninfected person, and the sneezing, coughing, nose-wiping, eye-wiping, we'll get into why I mentioned all of those things in a moment, person that is suffering from the flu. In other words, the closer you are to somebody who's sneezing or coughing, the higher probability that you will contract that cold or flu.

So we've already established two things. First of all, physical proximity is a key variable in terms of transmission of cold and flu. And at some level, that's sort of a duh. I mean, if you think about it, if you're in the next room or down the hallway from or across the street from somebody with a cold or flu, you don't expect to contract that cold or flu from them.

Whereas if you're in the same vehicle with them or you're sitting next to them on an airplane or you are on the same bus or in the same classroom as them and they are sneezing and coughing, well then, the probability that you would get that cold or flu from them is increased. That's just obvious.

But the studies that have explored the relationship between physical proximity and transmission of cold and flu have actually analyzed things down to the range of well, if you're standing one foot apart or you're standing three feet apart or six feet apart, what's the probability that you'll contract that cold or flu?

And it follows a very direct relationship where the closer the proximity, the more likely that you're going to contract the cold or flu from that person. And of course, anything like exchange of skin contact or exchange of saliva because obviously, in cases of romantic relationships where people will kiss or in familial relationships or friendships where people hug, any kind of contact also further increases the transmission of cold and flu.

Not just from stuff emitted from the nasal passages and from the mouth when people sneeze and cough but also when people wipe their eyes, even when people wipe their skin because oftentimes, they have cold or flu virus on their skin. It doesn't always survive terribly long on the skin. But if they wipe their face or wipe their nose or are using tissues and then don't wash their hands thoroughly afterwards, indeed, they can transmit cold and flu simply through handshake. So for all you hypochondriacs out there, I'm arming you with a lot of useful knowledge that will justify staying away from people who perhaps have cold and flu.

Now, this particular point about proximity and people being indoors more during the winter months, and that's why there's more cold and flu transmission, raises a whole bunch of interesting questions and in fact protocols that I plan to cover in a Huberman Lab podcast episode solely devoted to colds and flus and how to avoid getting colds and flus.

But one brief mention or telegraph of what I plan to cover in that episode is that if people are telling you that they are sneezing and coughing due to a cold or flu but that they are quote unquote, "not contagious" either because they are early in the cold or flu or late in the cold or flu and they have these theories or claims that oh, I'm no longer contagious, keep in mind that anytime someone is sneezing or coughing, they are in fact contagious.

So I'll get back to that in that full length episode about colds and flus. But I felt it was too important not to mention right now that people's theories about when they are quote unquote, "contagious or not contagious" are rarely substantiated by the actual data. The actual data point to the fact that when people are sneezing and coughing, if it's due to a cold or flu, they are still contagious.

So we've established that cold outside means people tend to be indoors more, which increases physical proximity, which is one of the reasons why there's more cold and flu transmission. One of the other reasons why being indoors more tends to increase cold and flu transmission is that in the cold months of winter, when people are indoors, they tend to be not under air conditioning, not at neutral temperatures but rather they tend to be in heated rooms. And depending on the type of heating that's used but in general due to all forms of heating, the heated air tends to be drier air.

Now this is a little bit counterintuitive because if you ever go outside on a really cold winter day, you will realize that the cold weather outdoors is extremely dry. You can almost quote unquote, "feel" the dryness of the air. And if you can't quote unquote, "feel" the dryness of the air or imagine what that's like, just imagine this.

Think of yourself outdoors on a very cold winter day taking a brisk walk. Then think about yourself taking that same brisk walk on a very humid summer day. Humidity is, of course, the concentration of water in the ambient environment, the air. Whereas, the dryness is the lack of humidity.

And just that little simple Gedanken or thought experiment will remind you just how dry the cold air is out of doors during the winter months. Whereas indoors, we're heating that air. And indeed, the heating of that air does have the property of drying the nasal and oral passages. But especially the nasal passages.

So another key reason why there's more transmission of colds and flus in the winter months is because people are spending more time indoors. And oftentimes, the way those indoor environments are being heated is drying out the nasal passages. And the nasal passages represent a primary site of defense for viral infections like colds and flus but also bacterial infections and fungal infections for that matter.

Now, I've talked before on this podcast about the importance of using nasal breathing under any conditions where you don't have to breathe through your mouth. So if you are not eating, if you're not speaking or if you're not exercising hard, which by the way oftentimes requires that you breathe through your mouth. There's nothing wrong with breathing through your mouth if you're exercising hard and you need to breathe through your mouth in order to bring in enough oxygen. There are conditions under which that's entirely appropriate. You can learn more about that in the podcast episode I did all about breathing and breathwork.

But for the most part, it's best to be a nasal breather except under the conditions I just mentioned. Why? Well. The nasal passages contain a number of physical barriers, including the hairs within your nose. I know that hairs in the nose, especially if they are super numerous, are not considered aesthetically nice. People will trim them, et cetera. But those hairs in your nose actually serve as a barrier toward infection. This is well-established.

The lining of the nose, the mucosal lining of the nose contains a lot of things. First of all, it acts as its own physical barrier and physical trap for incoming viruses, fungal infections, and bacterial infections. They literally get trapped in the nasal passages and therefore can't enter deeper into your physiology. And right now is not the time to go into the whole anatomy and physiology of the nasal passages.

But keep in mind, if you saw the episode that I did with Noam Sobel or you listen to the episode that I did on olfaction, both of those episodes highlight the fact that your brain sits not far behind your nasal passages. There's a bony barrier there called the cribriform plate and there are some other things as well. But it's not far from your nostrils to your brain. And it is not far from your nostrils to the rest of your respiratory pathway, of course.

And so the hairs of your nostrils, the mucus itself, and the microbiome, the trillions of little micro bacteria that thrive in the mucosal lining of your nasal passages actually serve to protect against many of the incoming infections. This is why it's so important to keep the mucosal lining of your nasal passages thriving and intact. How do you do that? Well, one of the best ways to do that is to make sure that the air that you're breathing is sufficiently humidified.

So while there are many different claims out there about how to avoid colds and flus, as long as we're having a discussion about why there are more colds and flus in the winter months, because indeed there are, it's worth mentioning that if you suffer from colds and flus and you're going to spend a lot of time in particular indoor environment, you might be wise to find air humidifier, something that brings more moisture in to the air that you're breathing especially at night while you're sleeping.

Now, that's not going to prevent the person in your environment who happens to have a cold or flu and is sneezing actively from transmitting that cold or flu. But it will keep your nasal passages and the rest of your respiratory pathways as healthy as they can be and as resistant as they can be to any colds or flus that you might be fighting off.

And this is another key point, which is regardless of whether or not it's the winter months or the other months of the year, all day long, you're combating different types of infections. Different types of viral, fungal, and bacterial infections are bombarding your system, and your immune system counters that both through physical and through neurochemical and hormonal and pure immune mechanisms.

There's a whole discussion of this in the episode that I did on the immune system. We'll do more on this. But keeping the air that you breathe, especially at night, sufficiently humidified is one great way to try and offset colds and flus that you might be combating because you brought that cold or flu home from work and your immune system needs to ward it off.

If you are having a hard time grasping how it is that you could bring home a cold or flu and then ward it off, like, do you have it? Do you not have it? Is it sitting there trying to get into your system or do you have it a little bit? Well, this is some of the gray area around cold and flu and viral transmission generally.

I mean, we don't know, for instance, if you got a mild sniffle as opposed to a really bad cold or flu, whether or not it would have been a really bad cold or flu. Had you slept less? Had you not humidified your air better? Et cetera. Probably it would be. And if you've ever not slept well for a little bit and you're sick, you experienced just how much worse that sickness feels. The symptoms of that sickness go from very mild to moderate or from mild to moderate to very severe when you are sleep-deprived.

That said, it's also clear that some strains of the cold or flu can be more mild than other strains of the cold or flu. So this can be pretty nuanced, and we'll go deeper into this in the episode that I do on cold and flu and how to avoid cold and flu. But nasal breathing, whenever possible, day and night time is extremely important for encouraging the overall health and resistance of your respiratory pathways to incoming cold and flu and other types of viruses.

Similarly, humidifying the air that you breathe, especially at night. But perhaps also during the day in your office environment or home environment can also be very beneficial for warding off colds and flus. And if you'd like to read more about the nasal versus mouth breathing components of colds or flus, I'll just mention one paper now. And again, I'll go into this in more depth in the future episode on colds and flus. But I want to mention that this is a bidirectional effect, meaning people who deliberately breathe through their nose tend to get fewer colds and flus. Also, people who tend to breathe through their mouth more tend to get more colds and flus.

Now, you might think that's the same thing or just two sides of the same coin. But actually, it's not. There's what we call a double dissociation whereby if people are mouth breathers, they are far more susceptible to colds and flus and other types of respiratory illnesses.

I'll put a link to one particular paper that I like a lot in the show note captions entitled, association of oral breathing with dental malocclusions and general health in children. This paper explores a lot of different things about nasal versus mouth breathing, all of which, by the way, point to the fact that nasal breathing whenever possible is better for us health-wise, aesthetically, dental health wise than is mouth breathing.

But one of the key components here, and this is why I bring it up in the context of this discussion, is quote, "oral breathing is related to a significantly higher prevalence of allergies and a significantly more likely getting sick and taking medication for being sick." So lots in this study, lots in related studies.

But nonetheless, being a nasal breather, humidifying your air, paying attention to whether or not you're indoors with people who are coughing and sneezing because it's cold outside, all of those things are going to be relevant. Perhaps keeping a little bit of distance, maybe a lot of distance from those people or encouraging them to wash their hands after they wipe their nose. Maybe even sending them to a little bit of not necessarily isolation, although that might be necessary. But keeping them at a distance. I don't think it's too much to ask somebody who's sick to not get you sick. Personally, I think that's the polite thing to try and do.

And there's actually not many things ruder than someone who knows that they're sick showing up to something because they didn't want to miss that particular event and getting everybody else sick. Frankly, that's my opinion. I think that opinion is shared with many of you out there as well.

Now, as I mentioned earlier, when it's cold outside, the air tends to be drier. Not always. I mean, you could live in an environment that's very cold and very rainy. Obviously, very rainy is very humid. It's maximum humidity if you think about it. But if you are going to spend time out of doors in cold days of winter, which by the way, is a really good thing for other reasons. I'll get into those reasons in a moment because they relate directly to why there's such a prevalence of colds and flus because in general, people are not doing what I'm about to tell you to do. But there are two things to keep in mind if you're going to be out of doors.

First of all, all the things about proximity still hold. There have been studies of people who have colds and flus sneezing in indoor environments versus outdoor environments and how much transmission there is. Again, it boils down to proximity. Yes, you can get a cold or flu from somebody sneezing out of doors next to you just as well as you can if they sneeze next to you indoors. There's a slightly higher probability that you'll get it from them if they're sneezing at that same distance. But you're indoors as opposed to outdoors.

Obviously, sneezers, coughers. Sneeze and cough in the other direction. Cover your mouth and nose. If you don't have a tissue or something, we are told, and I subscribe to the idea that sneezing into your elbow or coughing into your elbow is probably the next best thing to not covering up at all as opposed to into your hand, which then you touch other things and yourself.

Anyway, without getting into the mechanics of sneezing and coughing too deeply, if you're going to be outside in the cold winter months and you'd like to avoid getting colds and flus, when you run, when you exercise, when you walk, when you're in conversation, try to nasal breathe unless you have to mouth breathe. And if you can sense your nasal passages or your mouth drying out because of that hard breathing--

And by the way exercise during the winter months is still important. So I'm not discouraging people from exercising outdoors during the winter months as long as you can do it safely. But if you feel those air passages drying out, just be aware that when you take those dried out air passages indoors and you're around other people that might have colds and flus, you are going to be more susceptible. So that's cause for taking a hot shower, perhaps if you have access to a steam room or humidifier and rehydrating those nasal and oral passages.

Now, if you're outside and running and you're breathing hard and your nasal passages are drying out, does that mean that you're more susceptible to colds and flus that are just out in that environment if no one else is around? Chances are, no.

However, what we were all told when we were kids, which is if you go outside and you get a chill, it's a good idea when you come back inside to take a hot shower or a hot bath or if you have access to a sauna and to a heat back up, that's also true. Why? Well, it does seem that there's a relationship between core body temperature and susceptibility to cold and flu. And this is something I'm going to go deeply into in the episode on colds and flus.

Keep in mind that fevers that are the response to exposure to a cold or flu or being full-blown sick with a cold and flu are an attempt of your immune system to heat up that virus and destroy it. Keep that in mind if you're considering taking any kind of medication to lower your fever. Of course, know that highly elevated body temperatures a.k.a. fever can be very dangerous to the brain and body.

There's a fairly limited upper range of temperatures that we can go into before we start damaging ourselves. But also keep in mind that fever is an adaptation designed to destroy viruses. So if you blunt the fever, you are actually letting a cold or virus to proliferate more readily than it would if you allowed a slight fever to combat that.

So there's a whole discussion to be had there because obviously, you don't want people cooking their brains due to elevated fever and not treating that fever. But you also don't want to reduce your core body temperature too much, which raises the question of things like cold plunges. Should you be taking cold showers and doing cold plunges in the winter months when it's already cold and you're susceptible to colds and maybe you're coming down with a cold? Should you do that?

Well, that segues into the next question that I'm going to answer for this AMA which relates directly to cold exposure and so-called cyclic hyperventilation breathing sometimes associated with so-called Wim Hof breathing but other forms of deliberate breathing as well. And how specific forms of deliberate breathing and how deliberate cold exposure can indeed be used to offset or even prevent entirely infection due to bacterial or viruses.

But if you're already coming down with a bacterial or viral infection, why cyclic hyperventilation breathing or why deliberate cold exposure may actually be the worst thing if you are already contracting or if contracted. If you are contracting or have already contracted a cold or virus. So we'll answer that question next.

In the meantime, just know that yes, indeed in the winter months, you are more susceptible to colds and flus because there's more of them going around. We talked about some of the reasons why they're going around and some of the things you can do to protect yourself against those colds and flus. There are a bunch of other things that you can do that are very valuable that we'll explore in the full length episode on colds and flus and how to avoid getting them. And I'm hoping you all stay clear of colds and flus these winter months. And now you have some tools to try and reduce the duration and severity of those colds and flus should you get one.

OK. So as I alluded to a few minutes ago, the next question is about cyclic hyperventilation a.k.a. Wim Hof breathing as well as deliberate cold exposure and trying to ward off or shorten the amount of time that one is sick with a cold or a flu. Now as I answer this question, I'm also going to take the liberty of expanding the question a little bit, so a little bit of editorializing here because I know that a number of people are probably also going to wonder whether or not they should exercise if they are feeling not well with a cold or flu or more commonly whether or not they should exercise if they feel like they quote-unquote, "might be coming down with something" or whether or not they should rest instead.

Now I want to emphasize that I think these questions are really great and really important because it's the winter months or it's the summer months. We all contend with this stuff. We are exposed to people on planes, at work, kids come home from school with different sniffles and coughs, and we don't know because there aren't clear data as to whether or not we should rest more or whether or not we should engage in specific practices in order to keep our immune system strong. And a lot of that has to do with the fact that the messaging around exercise, and cold exposure, and cyclic hyperventilation is very direct on the one hand, but also very complicated.

For instance, we hear that exercise, nutrition, and great sleep, and quality social interactions keep our immune system strong. And by the way everything about that statement is true. However, a few minutes ago, we were talking about how proximity to others also increases your risk of cold or flu and a lot of social interaction involves proximity to others. Now perhaps that's not the best example. But we also hear that exercise can improve our immune system. And indeed, it can. However, we also know that if you exercise too long and/or too hard you can actually deplete your immune system.

Now the immunologists out there will say there's no such thing as a depleted immune system. What we're really talking about here is making yourself more susceptible to colds and flus and other types of infections had you not exercised than if you did. Why? Because any sort of exercise that's going to create a meaningful adaptation, so a reduction in heart rate over time or a reduction in blood pressure over time, or hypertrophy muscle growth, or strength increase, or muscular endurance increase, any sort of exercise that actually will trigger that sort of adaptation requires that, in the short term, you actually raise your heart rate, or raise your blood pressure, or raise your inflammatory cytokines, or challenge the muscle in some way that you can't actually move a weight another inch.

And the adaptation that follows is you get stronger, or your heart rate is reduced at rest, or your blood pressure is reduced at rest, all topics that we covered in the four episode guest series with Dr. Andy Galpin and other episodes that I've done about exercise physiology. So what we're talking about here is that exercise is a form of deliberate stress to your muscles, to your cardiovascular system, depending on the form of exercise and so on that's designed to create an adaptation that makes your muscles, your nerves, in some cases, both, your heart, et cetera, stronger, better, capable of more output. Similarly deliberate cold exposure, we know, is a stressor. It causes the release of the catecholamines, dopamine, epinephrine, and norepinephrine, and does so to a very significant degree and over a long period of time of several hours.

So it's a deliberate stressor to induce the stress response you are controlling it. That's the deliberate part. And indeed, when those catecholamines are deployed, you are, in fact, more resistant to colds and flus for a short while. However, if the stressor is ongoing, so if you do too much deliberate cold exposure in one session or too many sessions of deliberate cold exposure, or if you do too intense of a workout, or you work out too long or too frequently, especially if it starts to impede your nighttime sleep, either the duration or quality of your sleep, well, then those stressors that in many ways can protect you and buffer you against infections actually can make you more susceptible to those infections.

So this is very important to point out. People often think, OK, I'm coming down with a cold or flu, I'm going to exercise and I'm going to fight it off. I'm going to run it out. And you hear all sorts of lore that comes from running coaches and old wives' tales and from just around town where people will say things like, well, if the illness is below the neck, if it's in your lungs, don't run or lift weights. But if it's just the sniffles, if it's just a head cold, then it's safe to do.

Look, there is 0 minus 1 solid evidence that statements like that are true. It is highly individual because it's going to depend on which cold or flu, which strain of cold or flu, where you are in the arc of that infection, your natural immune response, the other people you're around whether, or not you're getting continual exposure to that cold or flu and you're trying to fight it off because you live with a family member with that cold or flu or whether or not you had a one time exposure, all of this stuff is relevant. So the question is, can cyclic hyperventilation a.k.a. Wim Hof type breathing keep us from getting sick.

So let's just answer that question first, then we'll talk about deliberate cold exposure, and then we'll talk about exercise because all three of these things basically converge on the same answer. There are some data to show that cyclic hyperventilation breathing can indeed help ward off the symptom response to bacterial infection. So what I'm about to describe are the results of what I consider now a classic paper exploring so-called Wim Hof breathing. Wim Hof a.k.a. The Iceman is somebody who achieved notoriety for a couple of things. One is deliberate cold exposure. And he has embraced and indeed embarked on these very extreme instances of deliberate cold exposure. He holds world records, multiple world records in fact for duration of time in ice up to his neck and swimming under icebergs, things that, frankly, I do not recommend most people do.

But Wim Hof method involves deliberate cold exposure. But also cyclic hyperventilation breathing so we need to separate out those two components any time we're talking about Wim Hof methods. I also want to point out that whether or not you're going to explore cyclic hyperventilation of any kind, any kind not just Wim Hof type breathing, which is one type of cyclic hyperventilation breathing that you never, ever, ever-- yes, I said it three times-- combine cyclic hyperventilation with exposure to water, meaning that you don't do it in the bathtub, you don't do it in a swimming pool. Frankly, don't even do it standing in a puddle. Don't do it anywhere near water because, in fact, people have drowned due to doing cyclic hyperventilation and then either deliberately going into water or passing out while in water and they've drowned, OK?

So even though Wim Hof method includes deliberate cold exposure and cyclic hyperventilation, and it does so in a very specific manner, it's very important that any time you're going to do cyclic hyperventilation, that you not do it anywhere near water or while operating heavy machinery, or driving, or anything that requires important mechanics or breathing for that matter. OK, I really want to establish that. I don't just say that to protect me. I say that to protect you. OK, what is cyclic hyperventilation breathing. Cyclic hyperventilation breathing is deliberately inhaling and exhaling with vigor repeatedly. OK? Cyclic hyperventilation.

My laboratory has studied cyclic hyperventilation in addition to other types of breathing. Although, it has different forms. It generally looks something like this, a big, deep Inhale through the nose, so putting a lot of physical effort into maximally inhaling the lungs, and then either letting the air leave the nose or mouth passively. So letting it, quote-unquote, fall out of the nose or lungs, or actively exhaling. So it's either active inhale, passive exhale or it's active inhale, active exhale. OK, so for instance, it would look something like this. I'll just do a cycle of three of these Inhale exhales but cyclic hyperventilation typically would go 15, 20, maybe even 30 of these breaths.







OK? So that's three active inhales, active exhales, repeating that for 10, 15, 25, maybe even 30 inhale-exhale cycles is so-called cyclic hyperventilation. And it's known to cause the release of epinephrine and norepinephrine within the brain and body. That's well established. Now there are other hormones that are actively released very quickly and significantly so as a consequence of cyclic hyperventilation. There is a study entitled voluntary activation of the sympathetic nervous system and attenuation of the innate immune response in humans that was published in the proceedings of the National Academy of Sciences USA in 2014, which took individuals who volunteered for the study, injected them with bacteria E. coli.

When that happens, people get very, very sick, they get a fever response. They tend to feel nauseous. They often throw up. They have diarrhea and other symptoms of bacterial infection. None of that surprising.

However, it was shown in the study that people that do the cyclic hyperventilation component of Wim Hof breathing, so no deliberate cold exposure in this study, just the cyclic hyperventilation component of Wim Hof breathing, had significantly lower if not zero response, that is symptom response to the injection of E. coli. OK. Now that could be viewed as good in the sense that they didn't get the fevers or they had lesser fever. They didn't get the headaches. They didn't get the vomiting. They didn't get the diarrhea. But of course, the E. coli was in their system too. So you could argue that they didn't get the immune response that they wanted. OK?

But the point of this study that I think is interesting is that it shows not that cyclic hyperventilation itself can prevent the symptoms of bacterial infection response but that high levels of adrenaline and noradrenaline, also called epinephrine and norepinephrine, those are the same things, that can reduce the symptoms in response to a bacterial infection. Now the idea here is that the innate immune response, which is a kind of global immune response to any kind of infection, bacterial, or viral, or otherwise was suppressed. It was somehow bypassed by having high levels of epinephrine and norepinephrine in the bloodstream.

And some of that was actually confirmed in this study. And there are a few other studies that allude to that mechanism as well. Now the point here is that we hear so often that stress makes our immune system vulnerable. It, quote-unquote, lowers our immune system or lessens our immune system. And to some extent, that's true. It certainly is true for chronic stress and especially any stress that impedes our sleep cycles and has us sleeping less.

Keep in mind that getting enough quality sleep each night is the best thing, the absolute best thing you can do, not just for mood, focus, and alertness throughout the day but also to keep your immune system robust and able to ward off infections of all kinds. So prioritize sleep. I'm always saying this. And we've done multiple episodes about sleep. So you can find protocols for all of that at just by putting sleep protocols into the Search function.

But sleep, sleep, sleep is the foundation of mental health, physical health, and performance. And that includes immune system function. But despite the fact that chronic stress, especially stress that impedes our sleep can disrupt our immune system and make us more vulnerable to bacterial, viral, and fungal infections, acute stress. That is brief peaks lasting minutes to hours of adrenaline and norepinephrine can actually protect us in keeping away infections. How? Why? Well, if you think about it in an evolutionary adaptive response kind of way, there were probably trillions of instances in human evolution and probably tens of thousands of instances in your own life that you've had and that you will have when you had to mobilize, something needed to be done.

You didn't have time to eat. This isn't necessarily the thing of saber-toothed tigers coming to get you. This is deadlines. This is you have to raise children. This is you have to help others that are suffering in your family elsewhere. And you, quote-unquote, did not have time to get sick. And what many people find is that after a period of stress, when they finally relax, they go on vacation, they get some time off, they take the weekend, that's when they get sick. Why? Because those increases in epinephrine and norepinephrine, adrenaline and noradrenaline, that are the response that we call the acute stress response can actually ward off illness. And it actually mobilizes the immune system through neural connections, to the spleen and thymus, and other organs of the immune system.

OK? So this idea that stress depletes our immune system is true. But short-term stress, such as the type of short-term stress that we can induce with, for instance, cyclic hyperventilation or a brief, intense workout. Let's not forget, if you do 12 to 15 minutes of high intensity interval training, that's also going to spike your epinephrine and norepinephrine and dopamine as well. And yes, deliberate cold exposure, cold shower of one to three minutes, ice plunge or cold plunge, one to three minutes, will spike that epinephrine, norepinephrine, and dopamine, and do so significantly over many hours.

Will that help ward off infection? Well, from a purely logical standpoint, the answer is, yes, it will. However, if you're already coming down with a cold or flu and you're a little bit sleep deprived or if you were exposed to a cold or flu earlier that day and you haven't even realized that you were exposed, you're not feeling that a little bit of scratchiness in your throat, the little bit of malaise that sort of like, I don't feel quite right. You know, that thing that we all recognize for ourselves that, for instance, I don't get headaches unless I'm getting sick.

I get sick about once every, gosh, I'd say 18 to 24 months, I'll get a cold or a flu. That's sort of the statistics of my cold flu averages. There are some exceptions to that. But I don't tend to get headaches. I don't get stomach aches. So if I have a headache or stomach ache, I know something's off. Something changed. There's something incoming or there's something in my system rather that I'm combating. So everyone needs to know for themselves where they are in that trajectory of getting ill. And here's the recommendation I would make. Cyclic hyperventilation, deliberate cold exposure, intense workouts, all are great for enhancing the functioning of your immune system. And they have other benefits as well that we've covered in previous podcast episodes.

Again, you can find all of that at Some of the benefits of cyclic hyperventilation and deliberate cold exposure have been a bit overblown I would say things like increases in metabolism, et cetera, not that well substantiated. But increases in dopamine, norepinephrine, and mood, and alertness, very well substantiated in my opinion. When it comes to cyclic hyperventilation, can it quote-unquote boost your immune system? Well, in the short term, yes, by way of increasing epinephrine and norepinephrine.

Likewise, for deliberate cold exposure, but also likewise for exercise, provided the exercise is neither too long nor too intense that you're taking your system from activated in terms of a stress response plus the dopamine response, which gives you that kind of like post-exercise feel good, right? Runners sometimes refer to it as the runner's high. Although the runner's high probably has something to do with endogenous opioids as well that you naturally make. We're not talking about opioids you take but opioids that you naturally make on long runs and things of that sort.

But if you're exercising too long. And what do we mean by too long? Well, for most people, if we're talking about 10 to 15 minutes of warming up and then doing somewhere between 45 minutes to 60 minutes of intense resistance exercise with weights, or machines, or even body weight, that's a pretty long high intensity resistance training workout. If that workout extends to 75 minutes, are you going to deplete your immune system? Well, probably not. But there's a lot of cortisol associated with a workout like that.

That's actually part of what induces the adaptive response. But once you get past 90 minutes or 2 hours, well, then, chances are, if you're maintaining intensity for the duration of those work sets, especially if the rest periods are short, but even if they're long, you are indeed running the risk of, quote-unquote depleting your immune system. So you have to find the duration of workouts that allow you to feel good both during, hopefully, although some of those workouts can be very hard. So you might not quote-unquote feel good to you subjectively but that also allow you to feel not completely depleted afterwards. OK? Because that will place you into conditions of vulnerability.

So for instance, if you are around a lot of people with colds and flus or it's the winter months and you are aware because of where you live or the conditions you live in that you're going to be exposed to a lot more colds and flus, you would be wise to pay attention to some of the things we talked about earlier in this episode and that are covered in the future episode on colds and flus and avoiding colds and flus, that is a standard Huberman Lab podcast episode will be all about that, but also paying attention to the duration of your workouts or-- I should say and/or your deliberate cold exposure, if you're doing that, any kind of cyclic hyperventilation, and frankly, any kind of stress that's spiking your adrenaline, keeping in mind that what you're trying to achieve is, yes, a robust immune response that can be buffered, can be augmented, and enhanced by these deliberate stressors but that if those deliberate stressors are too frequent, or too intense, or if you're already coming down with something, my stance, based on the research of colds and flus and their transmission as well as the research on cyclic hyperventilation, the immune system, deliberate cold exposure, and exercise, both the neural, hormonal, and immune related effects of all of that, that you'd be best off getting some extra rest and then returning to those things when you're feeling 100% robust.

So twice already during today's discussion, I talked about things that people have done or that people can do in order to somehow reduce the symptoms of infection but that perhaps are not advantageous in the long run or maybe even in the short run. For instance, when we talked about fever, I mentioned that the fever is a natural response that your body deploys in order to kill off bacterial infections, viral infections, and in some instances, fungal infections as well. And I mentioned that if fevers are too high, it's actually dangerous for the brain and body. But that if you reduce your fever by way of medication or other methods, well, then you're also reducing the immune response that can kill off those infections.

So it's a delicate balance sometimes, although, sometimes it's very clear. For instance, if you're an adult and your fever response is just by a degree or so, taking medication to reduce that fever response will probably prolong the existence of that viral or bacterial infection in your body. Similarly, we talked about this experiment where people did Wim Hof a.k.a. Cyclic hyperventilation breathing. They'd been injected with E. coli, and as compared to the control group, they didn't have the symptoms of the immune response, the fever. Again, here we are back to fever. The headache, the vomiting, the diarrhea. But keep in mind, the E. coli still existed in their system. So the cyclic hyperventilation breathing actually made them less effective at warding off or destroying that infection.

OK. So what they did is they bypassed the immune response. And as a consequence, the infection or the foreign invader, I should, say still existed within them and longer than it would have had they not done the cyclic hyperventilation. So I don't want to confuse anybody. I want to be very clear, however. There are certain things that one can do to reduce the symptomology of infection, such as taking something to reduce your fever but that actually are going to extend the duration over which that infection exists within you. Right?

Similarly, doing cyclic hyperventilation to reduce the immune response to a bacteria like E. coli will allow that E. coli to exist within you much longer than it would have otherwise. So we have to understand that sometimes, indeed, the symptoms of the immune response are very unpleasant, things like fever, vomiting, diarrhea, but all of those symptoms exist as an adaptation designed to get you healthy again much more quickly. OK? So in order to make things very clear. If you're feeling healthy, by all means, explore cyclic hyperventilation. Again, never near water. And by the way, there are some other safety caveats there. Perhaps listen to the episode that I did on breathing or look at the newsletter that I did about breathing.

Again, all of which is available zero cost at because there are certain individuals like those who suffer from panic attacks, who should probably avoid cyclic hyperventilation breathing, and there are other forms of deliberate breathing that I offer up that are research backed that those sorts of individuals might prefer or probably should use if they're going to do deliberate breathing of any kind. There's also, by the way, a newsletter all about deliberate cold exposure, and that also delineates who perhaps should and shouldn't explore deliberate cold exposure. But just to keep things fairly simple, exploring cyclic hyperventilation, exploring deliberate cold exposure are generally fine if done safely according to the protocols spelled out in those episodes if you are not experiencing symptoms of cold, or flu, or other types of infection. If you are experiencing symptoms of cold, or flu, or other types of infection, I recommend that you not do cyclic hyperventilation, you not do deliberate cold exposure at that time.

Also, I recommend that if you're going to do deliberate cold exposure, there is no reason whatsoever to do deliberate cold exposure for more than one to three minutes and starting with even 30 seconds and building up to 3 minutes is plenty. We talked about the 11 minutes per week threshold that was established by Dr. Susanna Søberg and others. You can learn more about that in the episode I did with Dr. Susanna Søberg. But when I hear about people doing 10 minutes of deliberate cold exposure, OK, like that. If you can build up to it safely, fine. That's impressive. And by all means, do that if you can do it safely. Certainly not a place for most people to start.

But I can't tell you how many people have contacted me saying, you know, I worked up to 30 minutes in the ice bath, and then I got sick or I did six minutes a day, every day in the ice bath, and then I got sick. Well, it's no surprise because you're inducing a lot of stress repeatedly day after day after day. So consider what minimal effective dose is in the context of deliberate cold exposure or even cyclic hyperventilation. And I recommend, for deliberate cold exposure, starting with 30 seconds or so. But really one to three minutes, working up to that. Anywhere from, I don't know, three perhaps, or seven times per week, or maybe even just once per week, you're still going to derive benefits from that.

No need to extend that much longer unless you have a specific reason to do that. And under those conditions, please go about doing that safely. With cyclic hyperventilation, my laboratory published a clinical trial showing that five minutes per day of cyclic hyperventilation has certain benefits in terms of improved mood, in terms of increasing heart rate variability, and some other important metrics of so-called autonomic nervous system function that were beneficial. There were other breathing techniques like cyclic sighing, which turned out to be more beneficial than cyclic hyperventilation.

But nonetheless, if you want to explore cyclic hyperventilation, do it under conditions where you're healthy and use it as a tool, perhaps doing, I don't know maybe 1 or 2 rounds of 25 to 30 of those cyclic hyperventilation breathing approaches that I demonstrated earlier and that I talk about in the breathing episode and in the newsletter on breathing. Maybe do that anywhere from one to five times per week. But if you're starting to do 10 to 15 minutes of cyclic hyperventilation every single day, you may buffer, that is augment your immune system in the short run. But if you're confronted with a stressor of a cold or a flu virus because you came into contact with someone who had a cold or flu virus and you're doing that much cyclic hyperventilation every day, keep in mind that you are introducing exposure to a cold or flu virus on a backdrop of a lot of deliberately induced stress.

And then when it comes to exercise, I already mentioned that, for resistance exercise, after a warm-up, most people aren't going to be able to tolerate more than about 60 to 75 minutes, maybe even as short as 45 minutes, but certainly 60 to 75 minutes of high intensity output, whether or not it's short rest or long rest. And then when it comes to endurance exercise, it's highly variable because it has to do with conditioning and a bunch of other factors. But for myself, for instance, I do a long run once a week on Sunday. This was by the way covered in the foundational fitness episode that I did. Again, you can find that at I also did a newsletter on it. It's all very easy to find, zero cost. I do a long ruck of a couple hours, that is a weighted hike, or a run, which for me is long.

So anywhere from 60 minutes to sometimes 90 minutes on Sundays but not if I'm feeling run down. If I'm feeling run down, I'll shorten that to 45 minutes or maybe I don't do it at all if I'm really feeling rundown. I feel like I might be contracting a cold or flu or other type of virus. And then in the middle of the week, I do a 30-minute run. And then on Fridays, typically, although it could fall on any day depending on your schedule, I do so-called high intensity interval training. Basically, what I'm trying to do is get my heart rate very close to maximum or maximum for periods of about a minute with some rest in between over the course of about 12 to 15 minutes.

So does that mean that you shouldn't train for your half marathon or marathon that you shouldn't run 7 or 8 or 10 miles, no, absolutely not. If you're conditioned to do that, it's hard to imagine that you are going to deplete your immune system by doing that. You've built up to it. However, if you're somebody that's doing my sort of running regimen and then you go out and you run 10 miles on one day and you do 12 the next day or even 6 the next day, chances are you're going to deplete your immune system, you're going to place yourself into conditions of heightened vulnerability to viruses of all kinds.

So you really have to consider the stress of exercise, the stress of deliberate cold exposure, the stress of cyclic hyperventilation, and think about it in the larger context of what you're being exposed to in terms of colds, flus, or other viruses, and also think about it in the context of how much sleep you're getting, how quality or depleting your social interactions are, and there's no perfect mathematical formula. No one's walking around with something measuring their cortisol from moment to moment, thinking about how those cortisol spikes are relating to the probability that they're getting colds and flus. This is something that's learned intuitively over time. It's always, always learned by trial and error, that is, for instance, in my case, I can remember, I think it was back in 2018 I came back from a trip, I landed on Sunday. Monday, I did a morning workout.

And I decided to do something I rarely ever do, I did an afternoon resistance training workout as well. I did the low rep heavy stuff in the morning and I went back in the afternoon and did some higher rep volume type work in the evening. And indeed, that night, I had a little bit of tickle in my throat the next morning. That tickle had grown into a scratchy throat, and I got really sick that week. Now was it all the consequence of those two workouts in one day? No, it was the consequence of whatever I'd been exposed to, either during those workouts or in the days before. It was the consequence of being depleted. So you need to think about these stressors as, yes, they can enhance your immune system, they can build you up, make you more resistant, but done too often or too intensely, they make you more susceptible to colds and flus.

I'd like to take this time to thank you for joining me for this Ask Me Anything episode. And I'd like to thank you for being a premium subscriber to the Huberman Lab podcast. I'd like to remind you that, if I haven't answered your question already, that I will be doing these Ask Me Anythings every month. I will continue to sift through the questions that are on the premium website. And I would encourage you to put additional questions there and to upvote questions that you'd like to see the answers to. If any of the questions that I responded to today you didn't feel were thoroughly answered enough, then please add a new question there and point that out.

I will read all the questions that are there. And I will strive to answer them as thoroughly, concisely, and clearly as possible. Again, you can put those at And as always, thank you for your interest in science.


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