Essentials: How to Control Your Metabolism by Thyroid & Growth Hormone

In this Huberman Lab Essentials episode, I explain how two key hormones control metabolism and discuss tools to enhance their levels to improve metabolic health. I discuss the pathways through which the brain and body interact to produce thyroid hormone and growth hormone, and how these hormones influence essential processes like tissue growth and repair, body composition, and energy production. I explain how thyroid hormone levels are influenced by key nutrients, such as iodine, selenium, and L-tyrosine. I also explain how practices such as exercise, sleep, meditation and sauna can offset age-related declines in growth hormone, to optimize overall hormone health and metabolism. Read the full episode show notes at hubermanlab.com. Huberman Lab Essentials are short episodes focused on essential science and protocol takeaways from past full-length Huberman Lab episodes. Watch or listen to the full-length episode at ⁠⁠⁠⁠⁠hubermanlab.com⁠⁠⁠⁠⁠. Thank you to our sponsors AG1: https://drinkag1.com/huberman Eight Sleep: https://eightsleep.com/huberman David: https://davidprotein.com/huberman Timestamps 00:00:00 Huberman Lab Essentials; Hormones & Metabolism 00:01:41 Hypothalamus, Pituitary, Thyroid 00:03:22 Thyroid Hormone Functions, Tools: Iodine, Selenium, L-Tyrosine 00:07:55 Sponsor: Eight Sleep 00:09:27 Thyroid Hormone, Glucose & Metabolism; Thyroid Hormone Disorders 00:11:45 Growth Hormone Functions, Prescription Growth Hormone 00:14:41 Growth Hormone Release, Tools: Sleep & Bedtime Fasting 00:16:07 Growth Hormone Release, Tool: Meditation 00:18:21 Sponsor: AG1 00:19:24 Growth Hormone Release, Tools: Exercise, Warm-Up, Glucose, Cool Down 00:22:04 Growth Hormone Supplements, Arginine 00:24:07 Offsetting Age-Related Growth Hormone Decline 00:25:05 Temperature & Growth Hormone, Tool: Sauna Protocol 00:29:23 Sponsor: David Protein 00:30:38 Peptides, Sermorelin, Secretagogues, Risk 00:33:26 Recap & Key Takeaways Disclaimer & Disclosures Learn more about your ad choices. Visit megaphone.fm/adchoices

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Andrew D. Huberman?

  Welcome to Huberman Lab Essentials, where we revisit past episodes for the most potent and actionable science-based tools for mental health, physical health, and performance. I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. This podcast is separate from my teaching and research roles at Stanford. It is, however, part of my desire and effort to bring zero cost to consumer information about science and science-related tools to the general public. Today, we are going to talk about two hormones: thyroid hormone and its related pathways, and growth hormone and its related pathways, which arguably are the two hormones and two systems in the body

• 0:43Andrew D. Huberman?

  that are most significant for setting your overall level of metabolism. So metabolism is the consumption of energy, not necessarily eating, but it's the use of energy in the cells of the body for growth of tissues, for repair of tissues, and also just for day-to-day maintenance of function. These two hormones, thyroid hormone and growth hormone, we think of as related to metabolism of things in the body, keeping body fat low, and keeping muscles strong, and tendons strong, and repairing themselves, et cetera. But they are also key for brain function, for the ability to maintain cognitive function throughout the lifespan. So the big theme I'd like to introduce

• 1:26Andrew D. Huberman?

  is that metabolism isn't just about losing weight, but having a high metabolism, provided it's not too high, is great. It means that you will have more lean tissue, more bone and muscle, and less adipose tissue, fat. And we know that that's healthy. There are neurons in your brain in an area called the hypothalamus, which just means it's below the thalamus, hypo. It sits at the base of your brain, in the front. It's part of the forebrain. So it's more or less above the roof of your mouth, maybe about a centimeter or so, and then about a centimeter forward in most people. And neurons in the hypothalamus...

• 2:01Andrew D. Huberman?

  Release hormones that are called releasing hormones. So anytime you hear releasing, chances are those are neurons that are in your brain, and they extend little wires, we call axons, into your pituitary. And the pituitary releases a bunch of hormones into the bloodstream. And the pituitary releases things that most often have the name of stimulating hormone, because they stimulate organs. So, in keeping with the theme of thyroid hormone, you have thyroid-releasing hormone in the brain, tells the pituitary to release thyroid-stimulating hormone. And then the thyroid, which we'll talk about in a moment, releases thyroid hormones. The thyroid is a little butterfly-shaped gland that's right around the Adam's apple,

• 2:44Andrew D. Huberman?

  and it's got four little bumps behind it called the parathyroid gland. And it releases two hormones into the blood to stimulate different tissues and their metabolism. And those hormones are called T4 and T3. So if this is already sounding like a lot of information, it's really easy, I promise. Releasing hormone comes from the brain, stimulating hormone comes from the pituitary. And in this case, we're talking about the thyroid binding up that stimulating hormone and saying, "Oh, I need to release something," and it releases T4 and T3. And guess what? You can basically forget about T4. T4, it's not completely inactive, it has some roles, but T3 is the one that's more or less active. Now, what does thyroid hormone do?

• 3:25Andrew D. Huberman?

  The main role of thyroid hormone, of T3, is to promote metabolism. And that doesn't just mean the consumption of energy. It means the utilization of energy, including the buildup of tissues. So it acts on all sorts of target tissues in the body. It acts on muscle, it acts on the liver, it acts on the cartilage, it acts on the bone. It's involved in taking fats and breaking them down into fatty acids and converting those into ATP, which is an important thing for cells to use energy. It's also involved in taking sugars and turning those into energy. And yes, it goes to adipose tissue to fat.

• 4:09Andrew D. Huberman?

  We have different kinds of fat that we'll talk about today, but it goes to white fat and it liberates or helps liberate some of the fats from those fat cells and use them for energy. And this is why higher thyroid is associated with leaner bodies. Lower thyroid is associated with less lean bodies. One thing that's absolutely key and is actionable, we're right there already in discussing tools, is iodine. Iodine is most common in sea salt, in kelp and in seaweed. And most people can get enough iodine from the food they eat and/or the table salt they consume. Almost all table salt from all over the world, regardless of where you are, contains iodine.

• 4:54Andrew D. Huberman?

  The thyroid needs iodine in order to produce thyroid hormone. Iodine combines with an amino acid that we've talked about before called L-tyrosine. L-tyrosine comes from meat, from nuts. There are some plant-based sources as well. It is the precursor to dopamine. But in the thyroid, iodine combines or works with L-tyrosine to produce T3 and T4, the thyroid hormone. So you absolutely need sufficient iodine, you need sufficient L-tyrosine, and then you also need something else which is called selenium. Selenium is important in order for thyroid hormone to be made because of the way that it allows L-tyrosine and iodine to interact.

• 5:39Andrew D. Huberman?

  And the thing is, most people aren't getting enough selenium because they don't eat foods that are high in selenium. Now, how much selenium you need will depend on where you live. It actually varies country by country. Some countries I found say that you should get 100 micrograms, some say 200, some say 155. The average was about 155 micrograms, the countries I looked at. People who are trying to increase thyroid levels might want to consume more selenium. And if you consume a vitamin, of course, you want to make sure if it has selenium, that you're not overdoing it by consuming a lot of selenium-rich foods either. Brazil nuts are the heavyweight champion of foods to get selenium from. It has very high concentrations of selenium.

• 6:22Andrew D. Huberman?

  In just six or eight, Brazil nuts contain something like 550 micrograms.

• 6:28Andrew D. Huberman?

  Of selenium. It's also present in fish, ham of all things, contains a lot of selenium. For whatever reason pork does. I'm not a big consumer of pork. Beef has some selenium. But what's interesting, if you look at the sources, you know, pork, beef, turkey, chicken, cottage cheese, eggs, brown rice, they, what you want to understand is that they, they have something like 30 to 50 micrograms of selenium. So if you're not eating Brazil nuts, and I'm guessing most people aren't, then, and you're not eating a lot of animal-based foods, which I know many of you aren't, then you're probably not getting enough selenium. And again, you can have these levels measured, or you can just check what you're consuming and figure out

• 7:11Andrew D. Huberman?

  whether or not you're meeting the ration that you need in order to get healthy levels of thyroid. I also want to mention that for children, their daily requirements of selenium are much lower, as low as, you know, 30 or 40 micrograms for kids 14 years or younger. And again, that's micrograms, not milligrams. So again, look into what you need. But if you're somebody who's interested in keeping thyroid function healthy and productive, then you certainly want to make sure you're getting enough iodine, you're getting enough selenium, and you're getting enough L-tyrosine. And it's interesting, when you start looking at the various foods, especially highly processed foods, then you start to realize that perhaps many people, maybe you are not.

• 7:55Andrew D. Huberman?

  I'd like to take a quick break and thank our sponsor, Eight Sleep. Eight Sleep makes smart mattress covers with cooling, heating, and sleep tracking capacity. Now, I've spoken before on this podcast about the critical need for us to get adequate amounts of quality sleep each night. Now, one of the best ways to ensure a great night's sleep is to ensure that the temperature of your sleeping environment is correct. And that's because in order to fall and stay deeply asleep, your body temperature actually has to drop by about 1 to 3 degrees. And in order to wake up feeling refreshed and energized, your body temperature actually has to increase about 1 to 3 degrees. Eight Sleep makes it very easy to control the temperature of your sleeping environment by allowing you to program the temperature of your mattress cover at the beginning, middle, and end of the night. I've been sleeping on an Eight Sleep mattress cover.

• 8:38Andrew D. Huberman?

  For nearly four years now, and it has completely transformed and improved the quality of my sleep. Eight Sleep recently launched their newest generation of the Pod cover called the Pod 4 Ultra. The Pod 4 Ultra has improved cooling and heating capacity. I find that very useful because I like to make the bed really cool at the beginning of the night, even colder in the middle of the night, and warm as I wake up. That's what gives me the most slow wave sleep and rapid eye movement sleep. It also has snoring detection that will automatically lift your head a few degrees to improve your airflow and stop your snoring. If you'd like to try an Eight Sleep mattress cover, go to eightsleep.com/huberman to save up to $350 off their Pod 4 Ultra. Eight Sleep currently ships in the USA, Canada, UK, select countries in the EU, and Australia.

• 9:23Andrew D. Huberman?

  Again, that's eightsleep.com/huberman. If you're curious how thyroid actually increases metabolism, allows you to eat more, etc., it relates to something we covered last issue, which is glucose. Remember, when you eat something, blood sugar goes up, insulin is secreted from the pancreas, and it makes sure that blood glucose doesn't go too high, which can damage tissues, or too low, which can make you hypoglycemic. Thyroid increases glucose uptake by various tissues, in particular muscle and bone. It actually can increase bone mineral density, which is a really good thing as you get older. When I say older, I mean basically 30 and older. The reason you can recover more quickly from injuries if you have a healthy thyroid and healthy thyroid pathways is because you can consume energy.

• 10:08Andrew D. Huberman?

  That energy is diverted toward bone repair and muscle repair and cartilage repair. And so, the way it does this, again, is by increasing ATP. But, the whole idea here is that iodine, selenium, L-tyrosine allow thyroid to be at healthy levels so that thyroid then can take glucose in the blood and divert it to tissues for it to be used, in particular, your brain. And that's why the ability of your brain to use glucose, or ketones for that matter, is going to be aided by having healthy thyroid. So, Do the things, take the things, eat the things that are going to allow you to have healthy levels of thyroid hormone. If you're concerned about having excessively high or excessively low levels of thyroid

• 10:50Andrew D. Huberman?

  hormone, absolutely, look up what the symptoms are, talk to your physician, and there are a number of good treatments. I didn't talk about prescription drugs that can improve symptoms related to hypo or hyperthyroid. Of course, they have synthesized thyroid, so if you don't make enough thyroid, you can take thyroid, it's by prescription. If you have too much thyroid, sometimes they'll take out the thyroid gland, or they can administer drugs that will either block receptors, or will interfere with some of the pathways from the brain to the pituitary, or from the pituitary to the thyroid, in order to adjust thyroid hormone that way. So there are the big guns in terms of the treatments for different thyroid disorders,

• 11:35Andrew D. Huberman?

  but we're not talking about thyroid disorders. We're talking about how to get and maintain thyroid levels in healthy ranges, and some straightforward ways to do that through diet and supplementation. Next, we're going to talk about growth hormone. Growth hormone is a pretty straightforward one for you to understand now, because it follows the exact same logic as thyroid hormone. In fact, their functions are so closely overlapping, that you're probably going to think, you know, why do you have these two systems? So just very briefly, growth hormone-releasing hormone, so remember, releasing means it comes from the brain, comes from the brain, and tells the pituitary to release growth hormone. And then growth hormone is released into the bloodstream, where it goes and acts on

• 12:16Andrew D. Huberman?

  a ton of tissues, muscle, ligaments, bone, fat, et cetera, to increase metabolism. It sounds just like thyroid hormone, and they do work in parallel, and that's why we've lumped them together in the same episode. They increase metabolism, and repair and growth of tissues. Today, we're going to talk about the things that anyone can do to increase growth hormone, and there are reasons why certain people would want to do that. People that make "normal" levels of growth hormone, might want to do that as they age, because during puberty and development, the pituitary is churning out tons of growth hormone. It's responsible for the growth, not surprising, of the body and all its features, height just being one of those.

• 13:02Andrew D. Huberman?

  And so as we age, we make less growth hormone and that is one of the reasons why we recover more slowly from injuries. It's one of the reasons why we accumulate body fat and it's one of the reasons why our metabolism slows. And so growth hormone replacement therapy has been tremendously popular in the last 20 years, which is not to say it doesn't carry its problems. It does. Here's one of the major problems with injecting growth hormone. Not saying people shouldn't do this if the doctor has approved it or it's in keeping with their particular life goals, but growth hormone, if it's in levels that are too high, will cause growth of all tissues.

• 13:43Andrew D. Huberman?

  So not just muscle, not just reduction in body fat by metabolizing, you know, by allowing fatty acids to be pulled out of storage and used for ATP, but it will also cause increase in growth of the heart and the lungs and the liver and the spleen. And so this is the concern with abuse of growth hormone. So we're not going to be talking about abuse of growth hormone. We will, however, talk about tools that anyone can use to increase levels of growth hormone. Some of them are behavioral, some of them are supplement based, and some of them interact with behaviors and supplements. And what's cool about the discussion about growth hormone is that the tools that exist out there to increase growth hormone are very actionable.

• 14:26Andrew D. Huberman?

  There are things that can increase growth hormone 3, 4, 500% or more. And even though that's a short-lived increase, they can have very powerful effects on metabolism and on repair of tissues. So let's talk about those. As always, I want to emphasize, talk to a doctor before you do anything, including remove any treatments. Growth hormone is released every night when you go to sleep and it's released in the early part of sleep during so-called slow wave sleep. So, the two conditions that have to be met in order for growth hormone to be secreted regularly for tissue repair, et cetera, are you need to get into slow wave sleep,

• 15:08Andrew D. Huberman?

  that so-called deep sleep, and you need blood insulin and glucose to be relatively low. So, eating within two hours of going to sleep is going to suppress growth hormone release. That's very clear. So, what is special about this early phase of sleep? What in particular about slow wave deep sleep allows the pituitary to release growth hormone? So, the answer is, it's delta wave activity in the brain. Delta waves are these big, giant waves of activity in the brain that correlate with slow wave sleep, as opposed to faster waves of activity that associate with rapid eye movement sleep. It's the delta waves of activity, these sweeping big waves of activity in the neurons

• 15:51Andrew D. Huberman?

  that stimulate the brain to stimulate the pituitary, because once you understand that, then you have something to anchor to in terms of thinking, what are the things I can do in waking that will allow me to release more growth hormone, which for most people is going to be a good thing. Now, the delta wave activity and the slow wave activity in the brain being very important for growth hormone release, and growth hormone release being so important for metabolic functions and peeling away unwanted body fat and repairing tissues, et cetera, forces us to ask, well, what other things can we do in waking in order to increase growth hormone release? So, let's start with the ones that have a potentially big effect, but are a little bit harder to access. And for that, I want

• 16:36Andrew D. Huberman?

  to point toward a book, which is really kind of interesting. It's not focused on growth hormone, but the book is called Altered Traits. This is the book. It's an excellent book. Altered Traits by Goldman and Davidson. Science Reveals How Meditation Changes Your Mind, Brain, and Body. Very interesting book. For those of you that are interested in meditation, and perhaps those of you who are not, but are considering it, What they talk about in this book is the fact that meditation has two separate lines of effects. One of those lines of effects are things that change your state. So you're stressed, you sit down, you meditate, and you relax, and you go into a particular state. The other are the changes that occur over time, and those are changes in trait. So

• 17:21Andrew D. Huberman?

  personality can actually change with long bouts of TM meditation, or repeated meditation. In any case, the reason we're talking about altered traits today is because certain types of meditation can get people's brains into states that very closely mimic slow wave sleep. So what this means is for people that are interested in increasing growth hormone, a meditation practice that allows you to get into these slow wave delta-type frequency activity in the brain may be very beneficial, because as I mentioned before, that's what's gating growth hormone release. It's not just a circadian phenomenon, it's

• 18:05Andrew D. Huberman?

  actually controlled by these brainwaves. Now let's move to the things that one can do that have been shown to have, let's just be honest, pretty enormous effects on growth hormone release in waking. And these are things that are very actionable. I'd like to take a quick break and acknowledge our sponsor, AG1. AG1 is a vitamin mineral probiotic drink that also includes prebiotics and adaptogens. AG1 is designed to cover all of your foundational nutritional needs, and it tastes great. Now, I've been drinking AG1 since 2012, and I started doing that at a time when my budget for supplements was really limited. In fact, I only had enough money back then to purchase one supplement, and I'm so glad that I made that supplement, AG1. The reason for that is even though I

• 18:49Andrew D. Huberman?

  strive to eat most of my foods from whole foods and minimally processed foods, it's very difficult for me to get enough fruits, vegetables, vitamins and minerals, micronutrients, and adaptogens from food alone. And I need to do that, I also notice, and this makes perfect sense, given the relationship between the gut microbiome and the brain... That when I regularly take AG1, which for me means a serving in the morning or mid morning, and again later in the afternoon or evening, that I have. Right now, they're giving away five free travel packs plus a year's supply of vitamin D3 K2. Again, that's drinkag1.com/huberman to claim that special offer. One of the things that can have a dramatic effect on levels of growth hormone release in waking, as well as in sleep the following night, is exercise.

• 19:34Andrew D. Huberman?

  There are hundreds, if not thousands, of studies measuring growth hormone, both during or sometimes after exercise, or the following night. And the conclusion that one takes away from all of these is that exercise has to be of particular duration and intensity in order to get growth hormone release. So first, I'm just going to tell you what I found to be the maximum amount of growth hormone release as it relates to a particular form of exercise. The particular form of exercise is either weight training, or it can be endurance training, but the endurance training and the weight training actually have to be limited to about 60 minutes, not much longer.

• 20:17Andrew D. Huberman?

  A proper warm-up seems to accelerate the release of growth hormone once the hard work phase starts. So 10 minutes of warm-up or so was the number that I extracted from all these studies. And when you say warm-up, it doesn't mean just warm up the limbs and tissues that you're going to use so you don't get injured, actually warm the body. Getting the body warm as a warm-up seems to be important because temperature of the body seems to be an important condition or prerequisite for certain patterns of exercise to maximize growth hormone release. So if it's weight-bearing exercise, it would be getting close to that final repetitions where you can't complete them, but not pushing through those, or even going to failure,

• 20:57Andrew D. Huberman?

  but getting close, leads to anywhere from 300 to 500% increases in resting growth hormone levels, and 300 to 500% increases in growth hormone the following night when you go to sleep, which is incredible.

• 21:13Andrew D. Huberman?

  One of the other conditions that seemed to be important, again, was to have relatively low blood glucose, so probably not eating too close to exercise, or not ingesting a lot of sugars during the exercise. That was supported by the fact that ingestion of a sports drink that contains caloric sugar immediately flatlined the growth hormone levels. So, really interesting relationship between insulin, glucose, and growth hormone. And then, the other interesting thing was that even after the exercise, taking body temperature back down to normal levels relatively quickly seemed to be associated with these big spikes in growth hormone. Otherwise, what would happen is you'd get these big spikes in growth hormone, but if

• 21:56Andrew D. Huberman?

  the exercise went too long, or if body temperature remained too high for too long, then you didn't get the second increase in growth hormone the following night. Let's talk about supplements. So, this has been known about for some time, but arginine, the amino acid arginine, can increase growth hormone levels substantially. The levels and the amounts of arginine required to get big growth hormone release increases is pretty substantial. So, some people will take arginine before bedtime, some people will take it before exercise. The prerequisite, again, is low blood glucose. Blood glucose is high, it's going to quash the effect.

• 22:36Andrew D. Huberman?

  The amounts of arginine that people take are anywhere from 3 grams to 10 grams, or sometimes even more. Although, this is definitely a case of more is not better. There is a threshold at which growth hormone release is actually blunted by taking more than 9 grams of arginine. Now, 9 grams of arginine orally is a lot of pills, it's at minimum 9 pills, and it can cause some GI disturbance, right? People can feel nauseous, some people will throw it up. What's interesting, however, is that whether or not it's by mouth or by vein, taking arginine can dramatically increase growth hormone release, 400 to 600% above baseline.

• 23:20Andrew D. Huberman?

  So, these are huge increases in growth hormone. Now, here is something really important and interesting to note, which is that increasing arginine levels with the specific goal of increasing growth hormone release...

• 23:36Andrew D. Huberman?

  Can actually short circuit the effects of exercise on growth hormone. Several studies I looked at, looked at the interaction of taking arginine and the exercise, or just the arginine, or just the exercise alone. And so you don't, unfortunately, if growth hormone increases your goal, you don't unfortunately get to increase growth hormone 800% by taking arginine and exercising. It always seems to be clamped at about 300 to 500% increases. So hopefully that's clear. One thing that's particularly interesting to me, as somebody who's in his 40s, is that it's actually between ages 30 and 40, that the amount of growth hormone that you release each night is reduced by two to threefold.

• 24:20Andrew D. Huberman?

  And since everybody goes through this age-related decline very dramatically, it seems to me that the things that we're supposed to be doing anyway, like exercising, like trying not to eat too close to bedtime, trying to optimize sleep, all of these are wonderful tools that we should be pursuing and perhaps using, and they can actually offset the two to threefold decrease, right? If we're talking about a two to threefold decrease for people there in their 30s and 40s, and then we're talking about increases from exercise, or from, maybe from supplementation, but certainly from exercise of 300 to 500%, well then, all of a sudden, we're in a position to actually offset the age-related decline in growth hormone completely, just through behaviors. And I think that's quite interesting and quite powerful.

• 25:05Andrew D. Huberman?

  Now, I'd like to discuss a way that anyone can increase their levels of growth hormone dramatically. And when I say dramatically, I mean dramatically. I'll get to the numbers in a couple minutes. But we have to remember how growth hormone is released in the first place. Remember, it all starts in the brain, in the hypothalamus. The hypothalamus is a brain area that controls things like sexual behavior, temperature regulation, circadian behavior, meaning when you want to be awake and when you want to be asleep, aggression, all of that. There are other brain areas involved too, but it has a rich collection of different neurons involved in all these very basic functions.

• 25:45Andrew D. Huberman?

  Now, as we talked about, the releasing hormones, the growth hormone-releasing hormone, comes from neurons in the hypothalamus. Those then communicate with the pituitary, and the pituitary releases growth hormone, and then the growth hormone acts on all these different tissues, muscle, liver, cartilage, et cetera, body fat. Makes them use energy. That's why you lose body fat when growth hormone levels are high. It makes you grow muscle, strengthens bones, et cetera. Now, one of the things that has a profound effect on growth hormone levels, growth hormone release, is temperature. Now, the data on this are very strong, and the data come from

• 26:28Andrew D. Huberman?

  both animal studies and human studies. And if you're guessing which direction this is going to go, you can probably imagine that making animals or people warmer is the way to go if you want to increase growth hormone. Now, anytime you're going to increase temperature of yourself, or anyone else, or an animal, it is risky. I want to be really clear about this. Not everyone should engage in the behaviors I'm about to describe. But, and I should just say, the reason it's risky is it doesn't take much of a temperature increase in the brain to cook the brain, to cook neurons. And after that point, neurons can't come back, and people can die from hyperthermia. However, there are really strong data pointing

• 27:12Andrew D. Huberman?

  to the fact that sauna, aka deliberate hyperthermia, not too high, however, that sauna can increase the release of growth hormone and other hormones. And what's so dramatic about this literature is the size of the effects that are reported. Entering environments where it's very hot for short periods of time, anywhere from 20 minutes to 30 minutes, where the temperature is 80 degrees Celsius to 100 degrees Celsius, has been shown to increase growth hormone release 16-fold. That's right, 16-fold. That's 1,600%. Now, there are also

• 27:54Andrew D. Huberman?

  effects on other hormones, prolactin, cortisol, et cetera. So, the pattern that was described in this study, and there have been many studies now, endocrine effects of repeated sauna, were done in 17 humans. They actually had to do this three days in a row. And the pattern was to get into the sauna for 20 minutes, followed by 30 minutes of cooling, followed by 20 minutes sauna again, led to a five-fold increase in growth hormone. And then, by doing that... Day after day after day, on the third day, you would see these huge increases of like 16-fold, up to 16-fold. But these increases in growth hormone are tremendous. And what they probably stem from are increased activity of neurons

• 28:38Andrew D. Huberman?

  within the hypothalamus that stimulate growth hormone released from the pituitary. And that's probably because the growth hormone-releasing hormone neurons in the hypothalamus sit very closely and may even be intermixed with some of the neurons in the hypothalamus that regulate heat and body temperature. Remember, metabolism is in part a heat. It's like a furnace of how much energy you're consuming and using for building or for energy usage purposes. So sauna can be very, very interesting. And again, it's 20 minutes, 30-minute cooling, 20 minutes again. Proceed with extreme caution, but nonetheless, these are pretty extreme effects in terms of their abilities to increase growth hormone levels.

• 29:23Andrew D. Huberman?

  I'd like to take a quick break and acknowledge one of our sponsors, David. David makes a protein bar unlike any other. It has 28 grams of protein, only 150 calories, and zero grams of sugar. That's right, 28 grams of protein and 75% of its calories come from protein. This is 50% higher than the next closest protein bar. David Protein Bars also taste amazing. Even the texture is amazing. My favorite bar is the Chocolate Chip Cookie Dough, but then again, I also like the new chocolate peanut butter flavor and the chocolate brownie flavor. Basically, I like all the flavors a lot. They're all incredibly delicious. In fact, the toughest challenge is knowing which ones to eat on which days and how many times per day. I limit myself to two per day, but I absolutely love them. With David, I'm able to get 28 grams of protein in the calories of a snack, which makes it easy

• 30:08Andrew D. Huberman?

  to hit my protein goals of one gram of protein per pound of body weight per day. And it allows me to do so without ingesting too many calories. I'll eat a David Protein Bar most afternoons as a snack, and I always keep one with me when I'm out of the house or traveling. They're incredibly delicious, and given that they have 28 grams of protein, they're really satisfying for having just 150 calories. If you'd like to try David, you can go to davidprotein.com/huberman. Again, that's davidprotein.com/huberman.

• 30:37Andrew D. Huberman?

  There's a kind of new area that's developing now that I think deserves our attention, not because I'm encouraging it, but because it is happening. And those are peptides. So these days, you hear a lot about peptides. I'd like to clarify a little bit about what peptides are. Peptides is a really huge category of biological compounds. Peptides are just strings of amino acids, right? So we've talked about L-tyrosine, arginine, ornithine. Those are amino acids. Those are individual amino acids. And those are put together into little, small peptides, or they're what are called polypeptides, which are just longer peptides. Turns out that for any substance like growth hormone or growth hormone-releasing hormone, it's made up of different amino acids in different sequences, just like your genes

• 31:22Andrew D. Huberman?

  are made up of As and Gs and Cs and Ts, nucleotides in different sequences. It's like a recipe. Peptides tend to be short sequences of amino acids that resemble a hormone enough or resemble some other peptide enough that it can lead to the similar or same effects when you inject them. So for example, we make growth hormone-releasing hormone from our brain, which stimulates growth hormone from the pituitary. But people now will take things like sermorelin, S-E-R-M-O-R-E-L-I-N, sermorelin, which is not the entire peptide sequence of growth hormone-releasing hormone, but it's a subset

• 32:06Andrew D. Huberman?

  of those, then that stimulates the release of growth hormone from the pituitary. So this is not taking growth hormone, this is taking the stimulating hormone, or what's often called a secretagogue, or a mimic, all right? It causes a secretion of the hormone that one wants. Sermorelin is prescription. Do they work? Yes. Do they shut down your natural production of... Growth hormone releasing hormone. Well, there, the answer is yes, but some of these peptides actually have the effect of changing gene expression because as you recall, growth hormone in big increases in growth hormone that are short-lived like sauna, or I, you know, I should say, exercise

• 32:49Andrew D. Huberman?

  or arginine or sauna, it seems like has these huge effects. Those are transient, but when one is injecting over and over a constant level, you can put into action gene expression programs that can be long-lived. And let's say you have a particular tumor in the body. Tumors will grow when they see growth hormone, even if that tumor is unhealthy for you, right? You've got growth of tissues all over the body. So again, not promoting their use, but they're definitely out there. And so now, if you hear about them, or if someone's talking to you about them, now hopefully you have a better understanding about their underlying biology and you can think rationally about whether or not they are the right decision for you. Okay. Once again, covered an enormous amount of material. Hopefully now you understand thyroid hormone and what it does and a little bit about its

• 33:34Andrew D. Huberman?

  mechanism, or maybe a lot, and growth hormone and what it does and how both of them take care of our metabolism. They dictate how many nutrients we can eat and make use of. They can pull from body fat stores, repair muscle, repair cartilage. They really are incredible compounds and they are actionable. There are things that we can do, like getting that early phase of sleep, perhaps supplementing with arginine, maybe not. Hopefully getting adequate exercise, warming up properly, not making the exercise too long or too intense will help. Maybe sauna or things like it, you know, deliberate, safe hyperthermia, the emphasis on safe, might be things that are of use. So now hopefully you understand not just thyroid and growth hormone, but the logic

• 34:17Andrew D. Huberman?

  that underlies thyroid hormone, growth hormone, estrogen, testosterone, why we eat, why we stop eating, cholecystokinin, ghrelin. If these names don't mean anything to you, then perhaps go back and listen to those episodes. But regardless, I hope that you come away from this with a deeper understanding about these hormones, which are so powerful in controlling the way our brain functions and the interplay between the brain and hormones, because it is really a bidirectional conversation. The brain is telling the body what hormones to make. The hormones are influencing all the tissues of the body, but also telling the brain whether or not to eat more, or grow more, or think more, et cetera. So I really appreciate your time and attention. If you like this podcast and you're finding it useful,

• 35:01Andrew D. Huberman?

  Please recommend it to other people. And last but not least, I thank you for your time and attention, and above all, for your interest in science.

• 35:13Andrew D. Huberman?

  You