Researchers simulating humans living in a closed habitat while on deep space travel found that the human body balances its sodium levels in a cycle that is independent on the actual salt intake. They have published their findings in the journal Cell Metabolism.
Sodium is used by the body to regulate blood pressure and control blood volume. It also is used for osmotic equilibrium and pH. A cell is said to be in osomotic equilibrium when there is no water loss or gain while in the body. Sodium ions are used by the central nervous system for the proper function of its nerve cells.
Salt (Sodium chloride) is the prime source of sodium in the diet. It contains 40% sodium. The minimum physiological requirement for sodium is 500 milligrams per day while the DRI (Dietary Recommended Intake) is 2300 milligrams per day. Anything above 3400 milligrams may cause hypertension.
The body through the kidneys (as part of its renin-angiotensin system) regulate the sodium concentration of the body. As mentioned in the article (detailed below), the textbook explanation of sodium regulation is that when the body detects an uneven concentration of sodium in the fluids, the kidney will either retain or decrease water to maintain the optimal concentration. Thirst is a sign that the body needs more water to maintain this balance.
A 150 pound (70 kilogram) person would have 15 liters (~4 gallons) of water in his body. The sodium content maintained by the body in the water would be about 1.75 ounces (50 grams).
