Sodium is only naturally present in small amounts in most foods. Table salt is the main source of sodium. Processed foods in particular are rich in sodium (and chloride).

Sodium (symbol Na) is an electrolyte and is present in all cells and body fluids (blood and fluid surrounding cells). Healthy kidneys maintain a constant level of sodium in the body by regulating the amount excreted through urine and sweat.

The most important function of sodium as an electrolyte is the regulation of water balance and the acid-base balance. Sodium is also involved in the correct functioning of nerve impulses and muscles. Together with potassium, sodium plays a role in regulating blood pressure (and blood volume).