Salt – how it affects the brain and why we need it


Published: 19-02-2023

Almost 40% of table salt is sodium. It is the largest source of sodium in our diet. Its excess is unhealthy for many organs, but too little salt is equally harmful. Without sodium, our brain cannot function.

Role of sodium in nerve cell communication (action potential)

Salt is an essential ingredient for the functioning of nerve cells (neurons), because the sodium contained in it is involved in the action potential. It is the triggering of the electrical activity of the neurons, that is, the way the neurons communicate with each other. The axons of nerve cells secrete (release) neurotransmitters, i.e. chemical compounds that excite or inhibit the action potential of other neurons.

How does it happen? Normally, nerve cells are negatively charged, while the intercellular space is positively charged, mainly due to sodium cations. If a nerve cell receives enough neurotransmitters released from another cell, small pores open in the cell membrane and sodium cations begin flowing into the cell. This changes its charge from negative to positive and generates an action potential and releases neurotransmitters to the next cell. The cell then returns to its normal state by releasing sodium cations with what is known as sodium-potassium pump.

Drinking a lot of electrolyte-poor water, or sweating profusely during exercise on a hot day, can lead to symptoms such as dizziness, confusion, or coordination problems, precisely because a drop in sodium levels disrupts communication between neurons.

Two senses of taste

Everyone probably knows that we have taste receptors in the mouth, collected in the so-called taste buds that sense different flavors. It is our conscious sense of taste that makes us want to eat or drink what we like. In addition, however, we also have a second, unconscious system in the intestine. Research on this has been done with sugar, but it probably works similarly with salt.

In the intestine, there are neuropod cells, i.e. nerve cells that detect various molecules – some of them detect e.g. fatty acids, others amino acids, others sugar (as well as artificial sweeteners). When we consume sugar, neuropod cells send electrical signals via the vagus nerve to the brain and raise levels of dopamine, a chemical that is generally responsible for motivation. In this case, dopamine makes us want to take in even more sugar.

“Intestinal sense of taste” explains why we like to eat products that contain so-called hidden sugar. Such products often do not have a sweet taste that we can consciously feel, but our intestine can feel the sugar contained in them.

How does the brain detect sodium?

The brain is protected against the influx of various substances by the so-called blood-brain barrier. Only very small substances are able to enter the brain or those that are necessary for its functioning. Including sodium.

There are several areas in the brain where the blood-brain barrier is very weak, allowing substances and molecules to pass freely from the blood to the brain. One such region is the OVLT (organum vasculosum of the lamina terminalis), one of the circumventricular organs. Neurons in the OVLT detect e.g. whether the level of sodium in the blood is too low or whether the blood pressure is not too high or low and send signals to other regions of the brain. When needed, the right hormones are released that act on tissues in the body and can, for example, tell the kidneys to produce more urine to get rid of excess salt.

Thirst and water and electrolyte homeostasis

Salt has many important functions in the brain and body, including: regulates fluid balance, i.e. how much fluid we want to take in and how much we excrete. It also regulates salt cravings. We have a homeostatic mechanism that makes us tend to eat and drink salty things when our sodium levels are low and avoid salty things when our sodium levels are high. Salt also regulates cravings for other ingredients like sugar and carbohydrates.

There are two types of thirst: osmotic thirst and hypovolemic thirst.

Osmotic thirst is related to the osmolality of the blood, i.e. its concentration (the ratio of the amount of sodium to water). Nerve cells in the OVLT sense sodium concentration and send nerve signals to the supraoptic nucleus and the paraventricular nucleus. Neurons in the supraoptic nucleus, in turn, send signals to the pituitary gland, which deals with the secretion of hormones, including vasopressin (antidiuretic hormone). If necessary, this hormone is designed to prevent the excretion of water in the urine (it makes the kidneys produce less urine). If the sodium level in the blood is low, the supraoptic nucleus signals the pituitary gland to suppress the production of vasopressin, which in turn leads to more urine production.

Hypovolemic thirst, on the other hand, is associated with a decrease in blood pressure, which in practice is usually caused by heavy bleeding. Decreased blood pressure is also detected by neurons in the OVLT, and renin, secreted by the kidneys, also plays an important role. It activates angiotensin II, which leads to an increase in blood pressure.

In both types of thirst, even though we feel that we are simply thirsty, the body actually strives to absorb not only water, but also electrolytes, including sodium.

Water and sodium work together to retain water or excrete it.

In simple terms, if we have a lot of sodium in the body, it means that we have too little water (high blood osmolality). Two mechanisms then take place that aim to increase the amount of water in the body. On the one hand, the body retains water, i.e. it inhibits its excretion, and on the other hand, it causes a feeling of thirst, which makes us want to consume it. On the other hand, when sodium levels are low, we excrete water. In reality, however, the mechanism is a bit more complicated. For example, if we have a lot of sodium, the body will want to excrete the excess, and when excreting sodium, we will always excrete some water. On the other hand, if the level of sodium is low, then yes, we will excrete water, but if the level is low for a long time, the body will “notice” that we are getting rid of a lot of water and will start retaining it. All this to maintain the proper balance of sodium and water in the body, which is necessary for proper functioning.

Too much salt in the diet is harmful to many organs, including the heart, lungs, liver, but also the brain. A large amount of sodium leads to the accumulation of a large amount of water in the nerve cells, which causes the nervous tissue to literally swell. But just as bad is too little sodium. Water is then pushed out of the cells, causing them to shrink, which also disrupts their function.

What is the optimal amount of salt and water in the diet? It is difficult to quantify, because it depends, among other things, on your blood pressure, how active you are, and how much you sweat.

In general, our feeling of thirst, or lack of it, is a good indicator of whether or not we should drink. However, we cannot always trust this.

Our homeostatic water retention/excretion mechanism is not ideal as hormones including vasopressin are slow acting. Everything works well if we eat a salty meal. The nerve cells in the taste buds will detect this taste, which will make you feel thirsty and replenish fluids as a result. However, if the salt is mixed with other flavors, we may not feel it. We will increase the amount of sodium in the body, but we will not feel thirsty, and in a few minutes or hours we may feel tired because we will be dehydrated.

In addition, if we regularly consume large amounts of salt, the body gets used to high sodium levels and does not cause thirst when it should. Therefore, our appetite for salt or beverages is not always a good guide to how much salt and water we should consume. In practice, we often drink too little.

It is also worth knowing that food producers deliberately “cheat” our homeostatic system by combining salty and sweet tastes in foods. If we consume a lot of salt, at some point we start to feel that we don’t want salt anymore. It’s the same with sugar (or artificial sweeteners). We have a sweetness threshold, above which we lose our appetite for sweets. However, if a little sugar is added to salty food, it seems less salty to us, and similarly, salt reduces the sensation of sweet taste. Therefore, we will eat more of a salty-sweet product than if it had only salty or only sweet taste.

Salt and stress and anxiety

Near the kidneys are the adrenal glands, which secrete corticosteroids, including aldosterone and cortisol. Aldosterone acts on the kidney cells and inhibits the excretion of salts into the urine, while cortisol plays an important role in the stress response.

Therefore, there is a close relationship between the stress system and the “salt system”.

The role of the adrenal glands in the regulation of sodium levels is shown by studies on animals that had this organ removed. Normally, animals (including humans) prefer mild to moderately salty foods, and foods that are too salty (e.g. sea water) cause an aversion. When the adrenal cortex is removed, the threshold above which the food becomes too salty is greatly increased and the animal is tempted to take in very large amounts of sodium.

There are also studies (mainly in animals) showing that a diet low in salt increases anxiety.

Why? This is not entirely clear yet, and more human research is certainly needed. Low sodium equals low blood pressure, and this in itself can cause symptoms of anxiety, but it can also be independent of blood pressure.

The stress system is a generic system designed to deal with various challenges (stressors). It can be a psychological stressor, caused, for example, by problems at work or in a relationship with a loved one, but physical factors, such as infection, hunger or lack of water, are also stressors. The stress response is related to with an increase in blood pressure and heart rate, which allows us to work more intensively. Short-term stress also stimulates the immune system so that we can cope with the challenge. Low levels of sodium can reduce our ability to cope with stress, while increasing the amount of salt can increase blood pressure and thus improve functioning under stress.

Some people, when under stress, have an increased appetite for salty foods. The body naturally tells them that they need more sodium.


Using Salt to Optimize Mental & Physical Performance | Huberman Lab Podcast #63

Author: Maja Kochanowska

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