Minerals and trace elements - Sodium
Sodium is responsible for regulating body water content and electrolyte balance. The control of blood sodium levels depends on a balance between sodium excretion and absorption at the kidneys, which is regulated by nerves and hormones. Sodium is also required for the absorption of certain nutrients and water from the gut. Sodium is a component of common salt, known as sodium chloride (NaCl).
As with some other minerals, sodium levels in blood and tissues are under homeostatic control. The kidneys tightly regulate sodium concentration and can make the urine almost salt-free or excrete sodium in urine when supply is excessive. Sodium intakes in the UK are considered to be too high and so deficiency of sodium is unlikely but under some circumstances losses can occur:
- Excess sweating:, e.g. due to exercise in a hot environment, may cause some sodium depletion.
- Diarrhoea can cause fluid loss and dehydration leading to some sodium depletion.
- The kidneys normally act to protect the body’s stores of sodium, but in Addison’s disease failure to produce aldosterone (hormone that allows the kidneys to retain sodium and water) leads to the kidneys inability to conserve sodium.
- Renal failure: The kidneys may also lose sodium in some types of renal failure.
- Drugs: Diuretic drugs may remove large amounts of sodium in the urine.
High sodium intakes, along with obesity and high alcohol intake, are considered to be among the risk factors for high blood pressure (hypertension), which is a risk factor for cardiovascular disease and stroke. A low salt diet may be used in the treatment of hypertension.
Most raw foods contain very small amounts of sodium chloride (salt). But salt is often added during the processing, preparation, preservation and serving of foods. The Food Standards Agency’s 2008 urinary sodium survey assessed salt intakes in the general adult population in the UK and showed that some progress had been made towards the 6g/day target for adults. The survey showed a reduction in the UK’s average daily salt consumption from 9.5g to 8.6g since the National Nutrition and Diet Survey (NDNS) in 2000/01. Work continues to reduce the amount of salt present in the food supply. To date much of the emphasis has been on foods sold through supermarkets but food consumed outside the home is also beginning to be targeted by the FSA’s activities.
The public also has a role to play in restricting the addition of salt to their food in the kitchen and at the table. About 20% of salt consumed is added at home during cooking and at the table.
© British Nutrition Foundation