Let’s find out the role of sodium (salt) in the nervous system and the key role that it plays in mental performance, physical performance, and health. The brain senses salt levels in our body, and that relates to our feelings of thirst.
Conscious and unconscious salt intake and sensing modulate cravings for sugar, water, and other things. There is a direct relationship between the stress system (glucocorticoid system) and the salt craving system if you’re feeling anxious or stressed.
Brain-gut connection & its role in taste
- Neurons activated in the gut are activated when sugar, fatty acids, and amino acids are present
- Nerve cells in the gut are collecting information about what’s there and send that information up to the brain
- Neuropod cells sense nutrients, particularly sugar, which activates areas of the brain that cause you to seek out more of that food
- The selective preference for seeking out sweet foods occurs even if you can’t taste the food and it is injected straight into the gut
- The gut can detect the difference between sweet things that contain calories and things that do not (artificial sweeteners)
Types of thirst
- Osmotic thirst (concentration of salt in the bloodstream);
- Hypovolemic thirst (thirst related to drop in blood pressure)
The cascades are set off for concentrations of both high and low sodium in the blood.
- Osmotic and hypovolemic thirst are not just about seeking water – they’re also about seeking salt which can help retain water
- Sodium engages the action potential, which is the firing of electrical signals by neurons
- If you ingest too much water (this requires A LOT of water), you will actually kill yourself because you’ll disrupt the body’s ability to communicate, brain, and neurons
Kidneys: It’s a complicated, highly contextual balance between hormones, salt, and fluid
- The kidneys are responsible for retaining and releasing substances in the body such as glucose, amino acids, urea, uric acids, salt, potassium, etc.
- Very general mechanism: blood enters the kidney and responds to hormonal signals to make mechanical or chemical changes to retain or release substances accordingly
- Your urine is filtered blood!
- Vasopressin: anti-diuretic which prevents urination by increasing permeability of distal tubes
- Water follows salt: the kidney holds on to water in the body when it needs salt
- When estrogen levels are high, there’s water retention
General functions of salt
- Fluid balance: salt regulates how much fluid you desire and how much you excrete.
- Salt appetite: you crave salty things when salt stores are low and avoid salt when stores are high.
- Nutrient appetite: salt regulates appetite for sugar, carbohydrates, and other nutrients.
- Scientifically, table salt and sodium are not the same things – one gram of table salt contains 388 mg of sodium.
Blood pressure and salt intake
- Blood pressure is in part regulated by sodium intake and sodium balance
- An increase in sodium could help combat symptoms of low blood pressure
- Historically, we’ve been taught that a high salt diet may be consequential for brain function
- However, high salt diets are likely related to other unhealthy factors like processed foods, poor balance of carbohydrate and fat, etc.
- A high salt diet can have detrimental health consequences – but – a very low salt diet can also have deleterious health events
Functions of salt in the brain
The blood-brain barrier prevents substances from entering the brain unless those substances are very small or required for brain function – but there are special areas (organum vasculosum of the lamina terminalis; OVLT) that monitor salt and osmolarity sense contents of blood and salt levels
OVLT detects changes to salt levels in bloodstream and sends signaling cascades accordingly – thirst, regulation of blood pressure, kidney function, secretion of salt
