a chemical element essential to life. Communications between nerve cells depend on letting sodium ions (electrically charged atoms) in through the cell membrane, and cells contain a mechanism called the ‘sodium pump’ which constantly removes the excess. Up to a third of the energy used by the cell goes to keeping this ‘pump’ running.
Sodium in its pure state is an inflammable metal and it is always found in compounds or, in cells, as ions (charged atoms). The most abundant sodium compound, and the form in which most sodium is consumed, is common salt, sodium chloride. Other compounds used in foods include bicarbonate of soda (sodium hydrogen carbonate) and Chile saltpetre (sodium nitrate). Caustic soda (sodium carbonate), the most powerful of all alkalis, is used to clean and disinfect kitchen surfaces.
In the body, it is essential to keep levels of sodium and potassium in balance. Almost always, any imbalance is an excess of sodium due to eating too much salt. The body's attempts to correct this can damage the heart. Doctors prescribe a low sodium diet, which in practice means not adding salt to food; ordinary foodstuffs provide enough sodium to maintain normal levels in the body.
Ralph Hancock is an encyclopedist with a special interest in food history and food science.
