January 31, 2024

AMA #15: Fluoride Benefits/Risks & Vagus Nerve Stimulation

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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.

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So without further ado, let's get to answering your questions. The first question is about fluoride, and the specific question is, why is fluoride in our water and how much is it harming us?

OK, well, that might seem like a short question, but there's actually a lot to that question. And I want to be very clear, by posing the question, how much is it harming us? It implies that fluoride is harming us. And I want to be very clear, the degree to which fluoride can harm you or not harm you depends on how much of it happens to be in the water or toothpaste or some other thing that you're consuming.

So this is very important. I don't want the question to seem like a leading question to imply that fluoride is necessarily harming us because as I'm about to tell you, there are clear benefits of fluoride for tooth strength and for warding off cavities. But if you get too much fluoride into your system, it is dangerous. It is a poison at certain levels. So as you've probably heard before, the dose makes the poison.

So let's take this seemingly simple question and dissect it in two. The first part of the question was, why is fluoride in our water? And believe it or not, even that is hard to answer directly because here's what's happening right now in 2024. There is a major lawsuit in the State of California to try and get fluoride removed from the drinking water.

The outcome of that case is still yet to be determined, but the case was filed by a group of individuals who strongly believe that fluoride at any concentration in the drinking water is bad. Why would they say that, and what is their evidence, and how strong is that evidence?

Well, there is some evidence that if levels of fluoride in drinking water exceed a certain threshold, it can cause problems with thyroid hormone function and perhaps even certain aspects of brain function. Again, if the levels exceed a certain threshold. So in the State of California, there is a major lawsuit to try and get fluoride removed from the drinking water.

Now at the same time, meaning right now, there is also a major lawsuit in the United States, this one taking place in Buffalo, New York, whereby citizens are suing the city because they insist that there is not enough fluoride in the water, and they are suing for damages based on the dental health needs of their children that did not, in their opinion, get enough fluoride in the drinking water.

So I'm telling you about all of this because the question, again, was why is fluoride in our drinking water? And believe it or not, there are certain states in the United States, certain areas of the United States where the fluoride levels in the drinking water are low-- are zero, perhaps-- that's what the lawsuit in Buffalo is about.

And by the way, the City of Buffalo may have now corrected the amount of fluoride in the water, taking it from zero to something. Whether or not it was actually zero is still debatable, but I think starting to get the point that there is a wide, wide divergence in terms of how safe people feel about having fluoride in drinking water.

Some people want it and are suing cities because they feel there wasn't enough of it in their drinking water, and others don't want any fluoride in their drinking water and they're suing cities because of that. So this is a really barbed wire topic, as I like to say. It's one that no matter how close you get to it, whatever angle you look at it, you're likely to get stuck a little bit, it's going to be a little bit painful.

OK. Why is fluoride in some drinking water at all? OK, let's set aside the levels and just answer that question. Well, in an upcoming episode of the Huberman Lab podcast about oral health, I'll get into this in a lot more detail, but fluoride is a really interesting compound with respect to oral health, and here's why.

Your teeth, believe it or not, are always in a state of either demineralization or remineralization. Those are tricky words to say. Go ahead and try and say it-- demineralization, remineralization. So I'm going to refer to them as "demin" for demineralization and "remin" for remineralization.

OK, your teeth are always in one state or the other, or one state predominates versus the other. Now a cavity in your mouth occurs when bacteria-- in particular, Streptococcus mutans, sometimes called Strep mutans, feeds on sugars in your mouth, and then as a byproduct of that feeding, creates acids that then erode the enamel and deeper layers of your teeth. In other words, it demineralizes the tooth.

Now I just told you that your teeth can be in a state of demin or remin at any moment. The way that your teeth remin, the way they're mineralize and can potentially fill in little cavities that have not yet made it to the deeper layers of your teeth is through a process that involves the construction of crystals from minerals-- that's why it's called remineralization.

And get this, this is really wild. These minerals actually stack together in very organized little sequences, kind of like LEGO blocks, and the critical element within those blocks is something called hydroxyapatite. I love that it has the word appetite in it because we're talking about oral health. That's the normal process.

Fluoride was discovered not because it's a vitamin, not because it's an essential nutrient. In fact, at high concentrations it's actually a poison-- I'll tell you a story about that in a moment where I was actually poisoned by fluoride at the dentist when I was a kid, in large part due to my own error. Fluoride, it was discovered, can actually get inside of those LEGO chain-like crystals, the building of those, and form bonds between them that are actually stronger than the hydroxyapatite bonds that would normally form.

In other words, if you consume fluoridated water or you use toothpaste with fluoride, especially if you do this when you're a kid, what ends up happening is that the crystals and the mineralization structure of the teeth becomes ultra strong, meaning super physiologically strong, which then limits the ability for that Strep mutans and the acid Strep mutans produces when it eats sugar to erode the enamel of your teeth, causing what we refer to as cavities.

OK, so I went and asked several dentists and a periodontist about why is fluoride in drinking water? Why is fluoride in toothpaste? And they, of course, gave me the explanation that I just gave you, which is a chemical mechanical explanation or rationale. However, most of the things for our health, such as the foods we eat, the amount of exercise that we do, are not naturally put into our environment, but tap water, which goes out to everyone who consumes it from the tap, is basically a government or local government-supplied resource.

And basically, the rationale was-- and I believe this took place first in the 1950s, was, OK, given the potential for fluoride to make super physiologically strong teeth, what can we do to reduce the cavities and tooth decay that would occur in children and adult populations? Let's put fluoride in the drinking water. So that's what they did.

They did not do this, I was told, because it was necessarily the best way to take care of teeth and avoid cavities. It turns out, there are a bunch of other things that you can do even if you consume no fluoridated water or toothpaste. There are things that you can do to enhance the mineralization state of your teeth-- even fill in cavities, provided those cavities haven't made it into the deeper so-called dentine layers of the teeth. I'll get into all of this in that future episode.

But what the US and other governments decided-- this, of course, varies across the world to the extent to which there's fluoride in the drinking water or not, was that by putting fluoride in the drinking water, they could prevent a large amount of tooth decay and cavities that would otherwise occur. It was and remains a fairly low-cost approach for these cities to introduce fluoride to the drinking water, and that's why fluoride is in drinking water. It is to try and create super physiologically strong teeth.

And indeed, every single dentist I spoke to, including functional dentists, I spoke to periodontists, I spoke to several dentists ranging from-- let's call them more traditionally trained dentists to more-- let's call them alternative dentists, all of them agree that at a chemical-mechanical level, fluoride creates stronger teeth.

However, every single one of them also acknowledged that the bonds that are created in those mineralization chains as I'm referring to-- I realize that's not the technical term, is not the normal hydroxyapatite bonds that would form. They are stronger than the bonds that would normally form. They are structurally different-- if you look at them down what's called an electron microscope, you'll see that they're structurally different.

And some-- not all of the dentists I spoke to-- said, yeah, it would be best to remineralize the teeth to fill in any cavities that initially have formed-- again, not down to the deep layers, but they could still be filled in naturally through the building up of those hydroxyapatite natural bonds, but they acknowledged that many people-- perhaps most people-- don't take adequate care of their mouths and their teeth, so they understood the rationale of putting fluoride into drinking water, and of course, that's also why fluoride is in many, not all, toothpastes.

OK, so I'm hoping that clearly answers for you the question of why there is fluoride in our drinking water at all, at least in most American cities, there is fluoride in the drinking water, although this lawsuit in Buffalo, I guess soon to be determined. Will probably tell us whether or not, indeed, there was a total lack or a partial lack of fluoride in the drinking water there. I'm presuming that the accusation is true, but I don't actually know that to be true.

I just know that there's a lawsuit that exists. If you Google that, you can see some YouTube videos about it. There's information about this happening. There are a bunch of angry parents. And I'm sure there are angry parents on the other side, and I don't know what the kids are saying, but hopefully no matter what, they're saying them through healthy teeth.

OK, now the second half of the question was, how much is the fluoride in drinking water harming us? I'm going to answer this question very specifically. The person asks, how much is the fluoride in our drinking water harming us? Well, I already told you ways in which it is helping the strength of your teeth. That's not debated.

Again, there might be some dentists that say, oh, the bonds that are formed by fluoride are different than the ones that are naturally created with no fluoride, and so there might be some debate about that, but all of them acknowledge that those bonds and the mineralization of the teeth is stronger with fluoride. They understand and agree with the rationale even if they don't necessarily agree with the practice as the best practice.

How much is fluoride in drinking water harming you? Well, there two things you need to ask. One is, how much fluoride are you actually drinking? Because it turns out, there's a tremendous range of fluoride concentrations in tap water depending on what city you live in. Now I did an entire episode of the Huberman Lab podcast about water. We talked about distilled water versus spring water, we talked about hydrogenated water, we talked about alkaline water, we talked about all of those things. And we did talk about fluoride.

And one of the key takeaways when you're thinking about fluoride in drinking water is to know that if fluoride concentrations in drinking water are too high or-- and this is a very important "or." Or you're consuming a lot of a particular water that contains even low levels of fluoride, well, there's the potential-- and again, I want to highlight the word potential here. I don't want to cause alarm-- that the fluoride is causing disruptions to thyroid hormone output, or on the receptor end-- in other words, disruptions to thyroid hormone metabolism and usage in the body.

OK, I want to be really clear here. I don't want people to think, oh, fluoride destroys your thyroid hormone. It's the dose that makes the poison. It depends on how much.

Now the Center for Disease Control have set a recommended level of 0.7 milligrams per liter-- 0.7 milligrams per liter of fluoride in drinking water as the level-- and here, I'm paraphrasing-- that can help prevent tooth decay and promote good oral health and that they have deemed safe. But if you want to know how much fluoride is in your drinking water, whether or not it is above, at, or below that value, you need to get your tap water tested.

Now fortunately, there are websites that can tell you how much fluoride is in your drinking water, and if you trust the data on those websites, you can simply put the city you live into one of those websites and you'll get the information back. I'll provide a few links to those different websites in the show note captions for this episode. We also provided those links in the show note captions for the episode on water. And then you can see, are you adjusting the level of fluoride in your drinking water that's deemed safe, less than that value, or more than that value?

But keep in mind, that if you drink a little bit, a moderate amount, or a lot of fluoridated drinking water, you're going to be consuming either more or less fluoride. Just because there's a concentration that's been deemed safe by the Center for Disease Control does not actually tell you whether or not OK if you're drinking half-a-gallon of tap water a day versus a gallon versus just a couple of cups, whether or not you are in that safe zone.

And of course, this is going to vary by body weight. If you're a small child, those lower levels of fluoride are going to equate to a larger total amount of fluoride as seen by the volume of the body. If you think about this, everything's by body weight volume and this is why drug dosages are most typically calculated as a function of pounds or kilograms of body weight. Not everybody gets the same dose of every drug. And if you're a very large person, maybe you can tolerate more fluoride.

As I mentioned before, high levels of fluoride have been shown to disrupt thyroid metabolism. It has also been hypothesized-- again, this is still highly debated-- hypothesized to be neurotoxic under certain conditions-- that is, toxic to neurons. It can kill neurons at certain concentrations, not necessarily the concentrations present in your drinking water.

A lot of the evidence that fluoride is neurotoxic is from so-called in vitro studies-- so studies done effectively in a dish, although there is some in vivo evidence that it can cause a neurotoxicity-- a.k.a., neurodegeneration.

So I think when it comes to the topic of fluoride, people tend to bin out into not concerned and simply want fluoride to strengthen their teeth. Mildly concerned, keeping an eye on this stuff. OK, fluoride doesn't sound great for me, but as long as the concentrations aren't too high, people will say, I've been drinking tap water my whole life and I feel great know my teeth are strong and my brain works and my thyroid seems fine. OK. And then people who are very, very concerned about fluoride at any concentration in their drinking water, hence the lawsuit in California-- and other lawsuits around the country.

So I believe that when we're talking about fluoride, you really need to think about the dosages and you need to ask yourself, which one of those three categories you fall into?

Now if you are concerned about fluoride, it does not necessarily mean that you can't drink tap water. The suggestion simply would be to filter that tap water. And during the episode I did on water, I talked about a number of different filtration approaches. Many of those filters will filter out fluoride and you can simply look up "water filters that eliminate or reduce fluoride."

And then some people have enough disposable income and/or are concerned enough about fluoride in their drinking water that they will purchase or create very extensive, very thorough filtration systems to completely eliminate fluoride from their drinking water. So you'll find different ranges of concern.

Again, aside from the data of high fluoride levels being disruptive to thyroid hormone pathways and possibly neurotoxic, I personally am somebody who filters the drinking water I consume out of the tap unless, that is, I'm going to boil water with it for making things like loose leaf yerba mate, which is one of my favorite drinks, although lately I drink this cold brew Mateina Yerba Mate, which, by the way, is made with purified water and no fluoride and so on and so forth.

But if I'm making rice or I'm making pasta or I'm making oatmeal and I need to use tap water, I don't worry about removing the fluoride from that water. However, if I'm going to drink water, if I'm going to mix an electrolyte pack in or just drink a glass of water or go out on a hike and take some water with me, I do use a water filter, either a filter that fills from the top and then seeps down and the ones you put in the refrigerator, or--

And I recently purchased a whole house filter for the drinking water taps in my house so that it does remove all the fluoride and removes some other contaminants as well. So it's going to depend on your level of concern and it's going to depend on your disposable income and any number of other things.

And I must say that every once in a while, I'll drink a little bit of tap water out of the tap without any concern about filtering the fluoride. I'm not somebody who gets hyper-concerned about these things, but I do understand why some people do get hyper-concerned about these things, especially people who've read up on fluoride and some of the health concerns of consuming too much fluoride.

Because I also find it very logical and understandable that as people learn more about how a particular substance might be harming their brain or bodily health, that they will become more concerned about consuming that substance. It just stands to reason.

So what am I suggesting? I suggest that you figure out how much fluoride is in your tap water. I suggest that you then make a decision as to whether or not to filter that water or not before drinking it. And then, of course, you have to make a decision about what sort of financial investment you're willing to make to filter that water.

You can find a list of different price ranges of water filters in the show note captions in the water episode. You may also want to watch that episode and go to that timestamp. And there's an enormous range there. I want to be very clear, I don't have a financial relationship to any of those filtration mechanisms.

Again, some people have zero dollars to devote to that process of taking the fluoride out of their water and other contaminants, some people have many, many tens of thousands of dollars, so it really just depends on your disposable income and your level of concern.

But if you were to ask me, I would say, yeah, I think given that the cost of most of the filters that can remove most of the fluoride is low and given that there is some health concern of consuming too much fluoride, why not just remove fluoride from the drinking water? And then if you say, well, won't that weaken my teeth?

Then I would say, well, watch the episode that's soon to come out on oral health because it's going to explain a lot of approaches, including fluoride-containing toothpaste, but some other non-fluoride-containing toothpaste and other things that one can do that the community of professionally-trained dentists all agree can really help improve the mineralization state of your teeth, and indeed, can fill in cavities that have begun to form but haven't yet made it to the deeper layers of your teeth and on and on.

Now I do have a brief story about fluoride that I'd be remiss if I didn't tell you, which essentially shows that fluoride is designed to strengthen teeth, but is also indeed a poison. So when I was a kid, I had a lot of dental issues. I didn't consume much sugar. My mother, fortunately, was good about not letting us consume too much sugar. But for whatever reason, my mouth was kind of a mess.

I'd brush, I'd floss, I would do all these things, but I actually had my adult teeth come in behind my baby teeth, so it didn't push out my baby teeth. So not only did I not collect from the Tooth Fairy, which I only recently discovered isn't real, but how would I know? Because the Tooth Fairy never showed up, because all of my adult teeth came in behind my baby teeth. So I had to have all of my baby teeth pulled on the top.

So I did not have a good relationship to the dentist as a location or a person. In fact, they had to tell me not to bite the dentist. By the way, I haven't bitten a dentist in a long time, so hopefully my dentist, if watching this, is not too concerned. I do get twice-a-year cleanings. I think every dentist agrees, that's a good thing to do. Some people may need less, some people may need more. But how do you know? You need to go to a dentist to find out.

Back to the story about fluoride. I started going to the dentist quite a bit because of all these dental issues that I had as a kid. And what they used to do-- I don't know if they do this anymore, but what they used to do is they give you these little trays, which are like mouth guards that you would use for boxing or hockey so your teeth don't get knocked out. And they would fill those trays with this jelly-like stuff that contained fluoride, and they put it on a top and on the bottom.

And the stuff just-- oh. Little bits of it would seep onto your tongue and your throat and it was so sour, it was so awful. And they'd seat me in this little wicker chair in front of a television and turn on cartoons as if that was supposed to make me forget how awful the whole experience was. If anything, it probably just created a Pavlovian-conditioned response to hate cartoons, which I suppose did not work because I liked cartoons then. I don't watch them now. Truly, I don't watch them now.

So I sit down on this wicker chair. I've got the fluoride in my teeth with these two trays and I'm just hating this whole process. I think I must have been about five or six years old. So I decide, in my infinite wisdom, to just swallow all the fluoride paste. So I start sucking it down through these mouth guards. I can feel it going back into my throat, and it's sour and it's stinging and it's awful, but I'm thinking, OK, I'm just going to do this. And I'm going to sit there I'm basically going to-- I'm going to beat the test.

And so I drink all this fluoride paste. And then, of course, I got immensely sick within about three minutes. I stood up, I turned around, and puked all over the wicker chair. I think that was deliberate. Actually looking back, it was deliberate. And puked all over the wicker chair.

My mom comes running in. What happened, what did you do to him? She was very protective of me. Thanks, mom. What did you do to him? And then I said, I just swallowed the stuff. They wanted to do it again and I stopped doing the fluoride treatment at that point.

Why did I vomit? Well, I vomited because fluoride is, indeed, a poison at high concentrations. Now do I tell you that story to make you afraid of giving your kids fluoridated toothpaste or fluoridated water? No. By all means, do what you think is best for you and for your children. For me, however, I've made some effort to avoid fluoride toothpaste.

I do go to the dentist, as I mentioned, about once a year. I confess, during the pandemic, it was probably less as they were busy and it was hard to schedule, et cetera. I've had very, very few cavities in my adult life. Hardly any.

And my gum health is very strong, et cetera, et cetera, largely through taking on protocols that I'm going to describe in the oral health episode and that were recommended to me by friends who are both dentists and other friends who are periodontists because again, there are a lot of things that we can do to strengthen our teeth in natural ways by building up those hydroxyapatite bonds, which are the natural bonds that teeth form, and yes, believe it or not, being able to reverse some early-formed cavities as long as they haven't made it deep into the tooth.

Also things like using a soft toothbrush because if you brush too hard, if you take that approach, you're going to brush your teeth really hard, get them really, really clean, yes, you'll scrape off all the biofilm, you'll avoid tartar build up, but you can really cause some tenting of the gum tissue above the teeth and those little recesses back in there are where bacteria get in.

And there's now a lot of really strong evidence showing that some of that bacteria can translate into cardiac disease, can translate into metabolic disease, and maybe even into some neurologic disease. So it's serious stuff. Oral health is one of the most important areas of health and it's one of the most overlooked areas of oral health, and I think people generally fall into two categories. And I'll use these two categories to frame up the episode on oral health that's coming.

One category of person seems really bullish on their oral health. They're like, keep my teeth white and clean and they floss and brush twice a day every day, and they use tooth whiteners and mouthwash and all those things. And the other category is blasé about it. Yeah, I brush my teeth in the morning so that my breath doesn't kill every person I get into an interaction with and so on and so forth.

But in reality, both the group of people that are doing an immense number of things to try and keep their teeth white and their breath fresh are, yes, doing things that are good for their oral health, but also no doubt damaging their oral health, in particular, the oral microbiome, which is absolutely critical.

And then of course, the other category of people that are neglecting their oral hygiene and are not taking mouthwashes and things like that are also damaging their oral health, but in different ways.

So during the episode on oral health, I'll spell out all the things that you can do, most of which, by the way, are completely zero-cost. Many of them actually will save you money, both in the short- and long-term, and can really help you improve your oral microbiome, the strength of your teeth, and reduce the number of cavities, maybe even reverse cavities that have begun to form and are not too deep into the tooth yet. And in a really nice way, all of that independent of your stance on fluoride.

OK, the next question is about the vagus nerve. By the way, the vagus nerve is the 10th cranial nerve that basically leaves an area right around the region of the neck, involves something called the nodose ganglion. Pretty cool name. And then goes down and extensively innervates the organs of the body. The heart, the lungs, the liver, the viscera. Even some of the musculature around them is influenced by the vagus nerve.

And then there are also vagal nerve pathways that go back from those organs up to the brainstem and can influence higher brain centers. Now that means that the vagus nerve, despite its name suggesting it's a nerve, like a single fiber bundle of axons, the wires that come from neurons is actually a superhighway. And it's a very divergent and convergent superhighway of nerve pathways. In fact, the word "vagus" means essentially "vagabond" or "to wander."

Because when early neuroanatomists started to chart the neural connections from the brain stem into the body and from the body back to the brain, they saw that it was this extensive superhighway, hence the word "vagabond," hence the name "vagus."

Now, the vagus nerve has been described gust prominently in pop psychology and popular wellness circles. So much so that it's generally believed that the vagus nerve is responsible for calming the body and the brain down. And the reality is, that is not true. It's simply not true.

There are conditions under which vagal nerve stimulation, either by electrical current or through specific breathing techniques that I'll talk about in a moment, or through other modalities such as pressure massage can cause a calming or a parasympathetic response. But, get this-- anytime someone tells you that vagal nerve stimulation or activating the vagus will calm you down, you just tell them, really?

Well, then, why is it that neurobiologists with laboratories use vagal nerve stimulation as a way to try and create more arousal and alertness-- that is, elevated activation of the sympathetic arm of the autonomic nervous system, the one that's sometimes called the fight or flight arm of the autonomic nervous system, although that's a bit too simplistic a name-- in order to try and alleviate depression or in order to try and wake up experimental animals or people undergoing neurosurgery who are drifting toward a coma state?

So the reality is that vagal nerve stimulation is not, quote unquote, "calming." The reality is that depending on which pathway, what neuroanatomists call which aspect or which branch of the vagus nerve is stimulated and how it stimulated, you can either get an elevation in alertness, maybe even an anxiety, or a decrement in alertness and an increase in calm.

Now I feel very passionate about this topic because as a public educator with my major background in neuroscience, it can be frustrating when people try to oversell the vagus-- or oversell any brain structure or neural circuit as doing just one thing. But, I must say, that by and large, I am a fan of most of the practices and most of the knowledge that's been put forth by others in the domain of vagal nerve activation for sake of calming people down or for reducing anxiety.

Now how can I say that based on what I just said a couple of minutes ago? Well, I think it's important, of course, to be accurate, but rarely are we able to be both accurate and exhaustive about what any given brain structure or neural pathway does, especially when speaking to the general public.

Now on the Huberman Lab podcast, I try to be as exhaustive as possible and offer as many caveats and disclaimers as possible to try and give the information in the most concise, and yet at the same time, accurate, exhaustive way, but I do understand why people have put forth the vagus as a calming tool. OK, I get it. And there are ways to calm yourself down through at least partial activation of the vagus nerve.

So let's talk about a couple of those methods because I think most people listening to this are probably thinking, OK, how do I calm myself down using my vagus nerve? Well, one of the better-established ways to do that is to take advantage of the fact that the vagus nerve interacts with some of the diaphragmatic pathways related to breathing.

Now if you've heard me talk about breathing on the Huberman Lab podcast or other podcasts before, what you'll immediately remember is that any time we emphasize the duration and the intensity of our exhales and we do it deliberately, we are going to slow our heart rate down. And that's through a different nerve pathway called the phrenic nerve, a spinal nerve, that innervates the diaphragm. The diaphragm is this muscle within the body that basically moves up or down depending on whether or not you're breathing in or you're breathing out.

There are many ways to activate the diaphragm through the phrenic nerve, but if you want to know where your diaphragm is and how it works, simply take an inhale through your nose and let your stomach, your belly, extend outward while you do that. You can try that right now. You can inhale and let your belly go out, and then exhale, belly goes in. So that's, no doubt, including your diaphragm, so-called diaphragmatic breathing.

Now you could also do it the other way. You can inhale and bring your stomach in. Exhale and bring your stomach out. That will also involve the diaphragm, but not as efficiently as letting your belly extend out a bit as you inhale.

So one way to quickly calm down, if you're feeling too much anxiety, alertness, or stress, is to just deliberately do an exhale through the mouth or nose, whereby your stomach moves outward. Now, again, that's accomplished by phrenic nerve-- by the way, spelled P-H-R-E-N-I-C-- phrenic nerve activation of the diaphragm, it will slow your heart down by virtue of some changes in the volume of your heart, the speed at which blood is pumping through your heart, et cetera. I've talked about this on other podcasts, so I won't get into the details now.

The fastest way that I'm aware of to calm down is to do the so-called physiological sigh. Many of you have heard of this before because I've spoken about it before. I didn't discover this, but it's a remarkable circuit built into your phrenic nerve pathway that will also trigger activation of the vagus nerve, which is what we're talking about now. The physiological sigh is a big, deep Inhale through your nose, then a second sharp, fast inhale to maximally inflate your lungs, and then a long two lungs empty exhale through the mouth. So this is performed in the following way.


OK, that's the fastest way to bring your heart rate down, to calm down. It works very fast in real-time. You might not even need to repeat it. Some people just achieve dramatic levels of calming very fast through one physiological sigh. Now what you didn't see and what relates to this discussion about the vagus nerve is that underneath my shirt, I was making very certain to make my belly extend-- go outward, that is, as I did those two inhales.

So as I do the inhale, my stomach is moving out.


Second inhale, my stomach moves out a little bit more, and then-- [BREATHS] the exhale the stomach moves back in. That's through that phrenic nerve innervation of the diaphragm, which then relates to slowing of the heart through a couple of different stations.

So here, what I'm saying is the fastest way to calm down in real time is indeed the physiological sigh, but if you want to make that even more effective, you'll recruit the vagal nerve pathway, which can be, at least to my knowledge, best accomplished by making sure that your stomach is moving out while you do the two inhales, and certainly the first inhale, and then when you do the exhale, two lungs empty through the mouth at the end, the stomach is moving in.

Try it both ways. Do a physiological sigh where you don't pay any attention to whether or not your stomach is moving in or out-- or actually, you could do it in a way where your stomach is actually moving in while you do the inhales, and then do a second physiological sigh where you're paying specific attention to making sure that your stomach moves out during the inhales and back in as you exhale. We'll take a little attention to doing this.

And what you'll notice is that you'll calm down to a much greater degree when you are certain to get that vagal nerve activation, or what I really should say, because we're being technical here, vagal nerve activation related to diaphragmatic breathing, that's going to calm you down even more than a physiological sigh would if it were done in the reverse way where the inhales are making your stomach move in.

So I realize we're getting down into the weeds, but this is an AMA for premium subscribers and here's where you can really get the fine tweaks on some of the protocols that we talk about on the Huberman Lab podcast and make them, especially effective for you.

Now, as I mentioned earlier, the vagus nerve has a lot of different branches. Some of those branches can indeed cause calming. Activation of those, for instance, can be accomplished through certain forms of organ massage. So for those of you that have explored some of the Eastern practices, there are certain organ-type massages where they will actually press on specific organs, and sometimes at two locations.

Some of that is done to benefit the organs directly. That'll be a topic for a future podcast. Some of it's done to transiently cut off blood flow pathways to particular organs then let that blood flow return. It's very interesting practices. In my mind, still needs a lot more mechanistic understanding, but some interesting stuff there. And then still, other aspects of organ massage are specifically to activate the vagus nerve.

Now unless you're a practitioner of those organ massage practices, I don't think that one can go in and just start pressing on their organs and learn to achieve the desired response. I think it requires-- I know it requires some extensive training, but that is the rationale behind those organ massage approaches.

Now in addition to physiological sighs done with the diaphragmatic inhale triggering the extension-of-the-belly-type breathing, in addition to organ massage, there are other ways to activate the vagus that can induce a calming response. One of the more interesting ones, I find, is the humming response. There's actually growing interest in humming.

James Nester has started to talk about this-- James Nester, of course, being the author of the fabulous book Breath, which is a book I highly recommend if you haven't read. It talks about the value of breathing in particular ways for physiological and psychological reasons, emphasizes nasal breathing whenever possible, et cetera.

But James more recently has been talking about humming. I think he talks about it a little bit in the book, but now he's talking about it more. There's a growing body of research on humming. Humming, it seems, can activate the release of certain things like nitric oxide, which is a vasodilator, allows more blood flow to various organs and tissues of the body.

Humming, provided it's done at a low frequency, meaning you're not humming-- [HUMMING] like up in your head, you're humming-- [HUMMING] where you can actually feel the fluttering down into the body is thought to-- small amount of literature, but growing amount of literature, showing that it is thought to activate some of the vagal pathways associated with calming.

Now, I want to be very clear, humming is not just activating the vagus, it's also an exhale. Think about it. [HUMMING] If you can hum while inhaling, I'm very impressed. Actually, you should probably see a neurologist. That was a joke. I'm sure you're fine even if you can hum while inhaling. But if you think about it, humming is actually a very low frequency, if it's done the way I'm talking about, a low-frequency slow exhale.

So again, we're getting back to exhales, we're getting back to activation of the vagus through long exhale breathing-- in this case, humming, which is also associated with nitric oxide release.

Now are we talking about humming like you would hum a tune? [HUMMING] Maybe. What we're really talking about is breathwork-style humming. I realize this is getting pretty esoteric, but here, we're talking about simply mechanical activation of neural pathways. I want to be really clear about this.

Anytime you're talking about a biological or physiological effect-- you could even call it a biohack, even though that's a word I loathe, because I like mechanisms, not hacks. But anytime you're talking about a biological or physiological effect, especially in human physiology, you need to think, are we talking about a mechanical or a chemical stimulation or both?

And when you're talking about humming or you're talking about long-exhale breathing, well, long-exhale breathing has a mechanical component. There's the moving out of the belly if you do it the way I described before. It also has a chemical component. There's a exchange. There's a differential in the amount of oxygen versus carbon dioxide that you're offloading. In fact, that long exhale out the end of the physiological sigh is to offload the maximum amount of carbon dioxide.

Carbon dioxide some people will refer to as the gas in the bloodstream that makes you anxious. That's not true. You need carbon dioxide in order to transport oxygen to your cells. So it's much more interesting than that, and we cover that in the episode on breathing.

But the point is that if you hear humming in order to activate the vagus nerve in a way that induces more calm, more parasympathetic activation, your first question should be, OK, is that mechanical or is it chemical or both? Well, in this case, it's probably mostly mechanical. It's probably activation of the phrenic and the vagus innervation of the viscera, organs within the big body cavity-- or the big portion, excuse me, of your bodily cavity. And-- [HUMMING] and mechanical stimulation there.

And it's also inducing-- and we know this to be true, that nitric oxide release that causes vasodilation. So a mechanical and a chemical aspect. Now, these are very simple, zero-cost, immediately accessible tools for vagal activation for sake of calming. There are, of course, devices now available for microstimulation of the vagus. This is being used to treat depression. But why is it being used to treat depression?

Well, it's being used to treat depression of the sort that people feel underaroused, understimulated. Too tired, not looking forward to the future. And these people get a vagus nerve stimulator that when-- and these are remarkable studies, by the way. I'll provide a link to a story about one in the show note captions-- that when you crank up the level of stimulation, it's been observed that people who are in really deep, dark depths of depression will start to say, I feel better. I can imagine a future in real-time.

Now that is not because of excessive calming down. That's actually the opposite. It's taking people who are depressed, who have low levels of energy, who are feeling very unexcited, even suicidally depressed about the future, and increasing their level of alertness and optimism. It's a remarkable effect.

Now the problem with some of those micro-stimulation treatments for the treatment of depression is that they have to be adjusted quite often-- and of course, requires the implantation of a micro-stimulation device.

The other issue is that because the vagal nerve pathways are braided with and interdigitated with other neural pathways, and because of the huge number of neural pathways within the vagus, sometimes those people will experience excessive coughing or challenges swallowing, or they'll feel like they're getting constriction of the throat, and this is why all of that has to be done in coordination with a very well-trained neurosurgeon and psychiatrist.

So there's a whole world to explore there, but it's a world that needs to be explored with licensed professionals. I do not recommend that people start buying vagal nerve stimulation devices commercially. And even while there are some of those out there, the ones that work from outside the body are not going to be very good at targeting the specific branches of the vagus nerve that are going to be required for the treatment of depression.

So if we take a step back now, we can say a couple of things in short-order form. One, the vagus nerve can cause both calming or increases in alertness. Two, there are mechanical and chemical consequences to stimulating certain branches of the vagus. Long-exhale breathing, diaphragmatic breathing being two of them, humming being a third, all of which are zero-cost and easy to access.

There's a whole landscape of micro stimulation devices used to stimulate the vagus in ways that increase alertness and can be used to treat depression. Those can have side effects such as challenges with swallowing or coughing. And now there is a plethora of commercially-available devices that activate the vagus nerve in specific ways in order to achieve or try to achieve specific outcomes.

And frankly, the science on most of those is rather scarce, but I promise, in a future episode of the Huberman Lab podcast, I'll do an episode all about commercially-available neurotech, by the way, with which we have no financial relationship-- I have no financial relationship-- just as a way to gauge whether or not these things work, what the rationale is for how they ought to work, and whether or not people are seeing success or even negative side effects with them. So I look forward to that episode.

Meanwhile, the vagus nerve is so fascinating. It's this super highway in you, in me and it has oh-so-many interesting effects. And before I close out on the vagus nerve, I'll just tell you about one effect that is very relevant for everybody, which is, as you recall earlier, the vagus nerve doesn't just consists of nerve pathways from the brainstem out to the organs of the body, but also back from the organs to the brain itself.

And there is a specific vagal nerve pathway that goes from the lining of the gut up to regions in the brain that then send on to yet further regions that stimulate the release of dopamine, which, as many of you know, is a molecule associated with motivation and seeking. More often than not, the seeking out of things that are pleasurable or at least that, in the short-term, are pleasurable. Sugar, sex, temperature, exercise, rewards of financial or relationships or et cetera.

The vagal nerve pathway that starts within the gut and then communicates with the dopamine system is sensing three things-- mainly three things, I should say. Essential fatty acids. So this would be your omega-3s, your omega-6s. Amino acids. In particular, the essential amino acids that come from high-quality protein foods. And sugar.

There are neurons in your gut that are activated-- that is, they send electrical impulses up through the vagus nerve to the brain to then stimulate the release of dopamine when you ingest things that contain sugar, amino acids-- in particular, essential amino acids from high-quality proteins, and essential fatty acids.

Why would this pathway exist? Well, this pathway exists, we believe, in order to get us to motivate-- to seek out more of particular foods that bring sugar, essential amino acids, and essential fatty acids because those three things are not just highly rewarding, but they are critical for our survival, perhaps much more so than other things out there because we need essential amino acids for muscular and tissue repair.

We need essential fatty acids for nerve cell and other cellular repair. Those essential fatty acids are actually brought into and become the building blocks of the cellular membranes of everything, from neurons to other cells in the body, but in particular, neurons.

And then, of course, sugar is highly rewarding, we know that. Even if you're somebody who doesn't like really sweet stuff like me, I don't know anybody that, at least at some stage of their life, didn't like a really delicious chocolate chip cookie or a really delicious piece of cake at some point in their life, maybe before they wean themselves off sugar.

Well, these neurons in the gut are essentially sitting there, and in an unconscious, completely unconscious way so you're not thinking about the taste of them in your gut-- you taste things in your mouth, as you recall, not within your gut.

But yes, the taste of sugar; yes, the taste of savory meat; yes, essential fatty acids will trigger a appetite of the sort that we're used to thinking about, the kind of mental and emotional appetite for certain foods, but at the level of your gut, the neurons of the vagus are sending signals up to the brain and getting you to seek out and consume more of those foods because your body can use those foods and really wants those foods.

Now do you need more of them? Not necessarily. That's where the taste of these foods becomes confounded with our absolute need for them. We tend to over-consume sugars. Most people probably don't over-consume essential amino acids from healthy sources, but some people do. We need essential fatty acids.

What the issue becomes is when people are consuming a lot of sugar and these neurons are getting activated, and then we're seeking out more sugar, and then we're not getting enough of the foods with the essential amino acids, such as high-quality proteins or high-quality fatty acids. And so I've often said to people, when they ask, hey, how can I quit my sugar cravings? Well, I'm not aware of any randomized controlled trial to support this. Maybe there is one, but I'm not aware of one.

One thing that I know by my own experience and the experience of many other people really can work to reduce those sugar cravings is to simply increase the amount of quality protein-containing essential amino acids that you consume and to increase the amount of essential fatty acids like omega-3s in the form of fish oil that you consume-- or another form of omega-3 fatty acids. Because then those neurons will essentially send signals to the brain where you seek out more of those particular foods.

In other words, you can do a sort of-- I guess in neuroscience, we would call this a silent substitution. You can, in an unconscious way, substitute the thing that activates those very same neurons so then you're seeking out the things that are actually healthy for you. And while I'm not someone to demonize sugar, I do believe that most people would do well to eat less sugar, less highly processed foods, and more high-quality proteins and more high-quality essential fatty acids, things like fish oil.

So you can pick your protein sources according to whether or not you're vegan, vegetarian, or omnivore such as me. I'm an omnivore-- proud omnivore. Can't put me in any camp because I'm in all of them. And in that way, control your appetite, get the nutrients you need. And yes, it's all being done via the vagus.

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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