Essentials: Using Salt to Optimize Mental & Physical Performance

This Huberman Lab Essentials episode, presented by Andrew Huberman, a Stanford professor of neurobiology and ophthalmology, starts from one claim: salt, or sodium, does far more than flavor food. It regulates fluid balance, both how much fluid we want and how much we excrete, and it also shapes appetite for other nutrients such as sugar and carbohydrates. The body tracks salt using small clusters of neurons called nuclei, which sense salt levels in the brain and body.

These sensing regions are unusual because of where they sit relative to the blood-brain barrier (BBB). Most substances circulating in the body, large molecules in particular, cannot pass into the brain, which the episode calls "a privileged organ in this sense." A few regions, however, have a weaker version of that barrier. The neurons that monitor salt balance and osmolarity, meaning salt concentration, sit just on the other side of these weak spots.

For this discussion, the most important of these regions is the OVLT, the organum vasculosum of the lateral terminalis. Its neurons monitor the bloodstream and can detect whether sodium is too low and whether blood pressure is too low or too high. The OVLT then signals other brain areas, which can release hormones that act on peripheral tissues. One example given is telling the kidneys to secrete more urine to get rid of excess salt.

Thirst is the episode's way into how the OVLT works. On this account, we get thirsty because OVLT neurons detect changes in the bloodstream that reflect changes across the body, and the OVLT then sets off events that make us want to drink more or stop drinking. The episode names two main kinds of thirst, osmotic thirst and hypovolemic thirst.

Osmotic thirst depends on the salt concentration in the blood. The example is eating a big bag of salty kettle potato chips, which raises blood salt levels and causes thirst. In the mechanism described, one type of OVLT neuron senses blood osmolarity. When salt concentration is high, these neurons send electrical signals to other brain areas, and the downstream result is that the posterior pituitary releases vasopressin, also called anti-diuretic hormone. Vasopressin restricts how much urine is produced. When the system is switched off, urine output increases.

Low blood sodium triggers its own set of cascades, but the episode says the pathway is the same. The OVLT detects the change in osmolarity and communicates with the supraoptic nucleus. Either vasopressin is released, or the system shuts off and urine flows more freely. As the episode explains it, "Anti-diuretic means anti release of urine," so turning the hormone off allows urination.

Hypovolemic thirst is triggered by a drop in blood pressure. Besides its osmosensing neurons, the OVLT has neurons in the baroreceptor and mechanoreceptor category. A baroreceptor is described as a protein in a cell that responds to changes in blood pressure. Causes of low blood pressure listed include heavy bleeding and, in some cases, a lot of vomiting, extensive diarrhea, or a combination of these.