In medical practice refers to Sodium Chloride (NaCl).
- It is an essential component of the diet.
- The body maintains sodium homeostasis to very strict tolerances mainly by regulating intake and output of salt
- The human kidney is inefficient compared to that of many other land animals in its ability to conserve salt.
- There is accordingly the potential for a fair salt loss each day through excretions such as sweat and urine.
- It is toxic if ingested with insufficient water to allow excretion of any excess on the daily loss
Throughout much of human history the availability of salt to many inland populations was marginal. However, such populations have intakes that are very close to the daily intake that studies have shown is the physiological set point of maximum efficiency in the homeostatic mechanisms. In populations that were able to use salt as a food preservative or had free access to salt due to location adjacent to the sea, intake would have been excessive.
A major consequence of excessive intake of sodium chloride relative to potassium chloride is believed to be essential hypertension. It may also be a risk factor1 for Type 2 diabetes There is strong evidence that the average population intake in modern diets is excessive in this way. The precise excess and its consequences is subject to debate. Certainly there is too much of it in commercially prepared food in Western Countries (often used as a flavour enhancer), considering the proportion of the average diet now made up from these foods.
- Sweat. Contains about 50mmol/l.
- Bowel. While losses are small in health, they can be marked with diarrhoea and/or vomiting. The usual cause of death in cholera is excessive salt loss.
- Renal. This is normally regulated to between 0.5 to 30 g a day to get rid of the excessive intake. The adult kidney can excrete between about 1 to 400 mmols of sodium a day. Immature kidneys do not have this dynamic range, and indeed babies run the risk of sodium poisoning from cows milk for this reason.
- To correct insensible losses. For example, execrise can lead to marked salt loss through sweating.
- To correct hyponatraemia due to excess salt loss.
- In solution, usually referred to as saline.
- ↑ O'Donnell MJ, Yusuf S, Mente A, Gao P, Mann JF, Teo K, McQueen M, Sleight P, Sharma AM, Dans A, Probstfield J, Schmieder RE. Urinary sodium and potassium excretion and risk of cardiovascular events. JAMA : the journal of the American Medical Association. 2011 Nov 23; 306(20):2229-38.(Link to article – subscription may be required.)