Essentials: Using Salt to Optimize Mental & Physical Performance

**Andrew Huberman** (0:00)
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. Today, we are going to discuss salt, also referred to as sodium. Salt has many, many important functions in the brain and body. For instance, it regulates fluid balance, how much fluid you desire and how much fluid you excrete. Salt also regulates your appetite for other nutrients, things like sugar, things like carbohydrates. We all harbor small sets of neurons. We call these sets of neurons nuclei, meaning little clusters of neurons that sense the levels of salt in our brain and body. There are a couple of brain regions that do this, and these brain regions are very, very special. Special because they lack biological fences around them that other brain areas have. And those fences, or I should say that fence, goes by a particular name, and that name is the blood brain barrier, or BBB. Most substances that are circulating around in your body do not have access to the brain, in particular large molecules. Can't just pass into the brain. The brain is a privileged organ in this sense. However, there are a couple of regions in the brain that have a fence around them, but that fence is weaker. And it turns out that the areas of the brain that monitor salt balance and other features of what's happening in the body at the level of what we call osmolarity, at the concentration of salt, reside in these little sets of neurons that sit just on the other side of these weak fences. And the most important and famous of these, for the sake of today's conversation, is one called OVLT. OVLT stands for the organum vasculosum of the lateral terminalis. The neurons in that region are able to pay attention to what's passing through in the bloodstream and can detect, for instance, if the levels of sodium in the bloodstream are too low, if the level of blood pressure in the body is too low or too high, and then the OVLT can send signals to other brain areas, and then those other brain areas can do things like release hormones that can go and act on tissues in what we call the periphery in the body. For instance, have the kidneys secrete more urine to get rid of salt that's excessive salt in the body. So let's talk about the function of the OVLT and flesh out some of the other aspects of its circuitry, of its communication with other brain areas and with the body in the context of something that we are all familiar with, which is thirst. Have you ever wondered just why you get thirsty? Well, it's because neurons in your OVLT are detecting changes in your bloodstream, which detect global changes within your body. And in response to that, your OVLT sets off certain events within your brain and body that make you either want to drink more fluid or to stop drinking fluid. There are two main kinds of thirst. The first one is called osmotic thirst. And the second is called hypovolemic thirst. Osmotic thirst has to do with the concentration of salt in your bloodstream. So let's say you ingest something very, very salty. Let's say you ingest a big bag of, I confess I don't eat these very often, but I really like those kettle potato chips. And I don't have too much shame about that because I think I have a pretty healthy relationship to food and I enjoy them. And I understand that it will drive salt levels up in my bloodstream. And that will cause me to be thirsty. But why? Why? Because neurons in the OVLT come in two main varieties. One variety senses the osmolarity of the blood. And when the osmolarity, meaning the salt concentration in the blood is high, it activates these specific neurons in the OVLT. And by activates, I mean it causes them to send electrical potentials, literally send electrical signals to other brain areas. And those other brain areas inspire a number of different downstream events. The consequence of that communication is that a particular hormone is eventually released from the posterior pituitary. So from the pituitary, there's a hormonal signal that's released called vasopressin. Vasopressin also goes by the name antidiuretic hormone. And antidiuretic hormone has the capacity to either restrict the amount of urine that we secrete or when that system is turned off to increase the amount of urine that we secrete. So there's a complicated set of cascades that's evoked by having high salt concentration in the blood. There's also a complicated set of cascades that are evoked by having low concentrations of sodium in the blood. But the pathway is nonetheless the same. It's OVLT is detecting those osmolarity changes, is communicating to the supra optic nucleus. Supra optic nucleus is either causing the release of or is releasing vasopressin, antidiuretic hormone, or that system is shut off so that the antidiuretic hormone is not secreted, which would allow urine to flow more freely, right? Antidiuretic means anti-release of urine. And by shutting that off, you are going to cause the release of urine. You're sort of allowing a system to flow. So to speak. The second category of thirst is hypovolemic thirst. Hypovolemic thirst occurs when there's a drop in blood pressure, okay? So the OVLT, as I mentioned before, can sense osmolarity based on the fact that it has these neurons that can detect how much salt is in the bloodstream. But the OVLT also harbors neurons that are of the baroreceptor-mechanoreceptor category. Now, more on baroreceptors and mechanoreceptors later, but baroreceptors are essentially a receptor, meaning a protein that's in a cell, that responds to changes in blood pressure. So there are a number of things that can cause decreases in blood pressure. Some of those include, for instance, if you lose a lot of blood, right? If you're bleeding quite a lot, or in some cases, if you vomit quite a lot, or if you have extensive diarrhea, or any combination of those, both types of thirst, osmotic thirst and hypovolemic thirst, are not just about seeking water, but they also are about seeking salt. In very general terms, salt, aka sodium, can help retain water, but sodium and water work together in order to generate what we call thirst. Sodium water work together in order to either retain water or inspire us to let go of water, to urinate. I'd like to take a quick break and acknowledge one of our sponsors, Function. 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Again, that's functionhealth.com/huberman to get early access to Function. So before we can dive into the specifics around salt and how to use salt for performance and various recommendations and things to avoid, we need to drill a little bit deeper into this fluid balance mechanism in the body. And for that reason, we have to pay at least a little bit of attention to the kidney. The kidney is an incredible organ. And one of the reasons the kidney is so amazing is that it's responsible for both retaining, holding on to, or allowing the release of various substances from the body. Basically, blood enters the kidney and it goes through a series of tubes, which are arranged into loops. If you want to look more into this, there's the beautiful loop of Henle and other aspects of the kidney design that allows certain substances to be retained and other substances to be released depending on how concentrated those substances are in the blood.