Sodium occurs naturally in many foods and is also added in the form of salt or other sodium-containing substances. Common salt or table salt is a chemical compound of sodium and chlorine and is called sodium chloride. The sodium content of food has important implications for health. Salt contains about 40 per cent sodium, and a teaspoon of salt, which weighs about 5 grams, contains about 2 grams of sodium.
Rock salt and sea salt are almost entirely sodium chloride, with only traces of other elements (minerals). In contrast to pepper, which loses flavour once ground, there is no advantage in freshly grinding salt prior to its use. Iodized salt contains about 0.03 milligram of iodine per gram of salt. It is intended as a supplement for people whose diet is deficient in iodine. Recent findings in the U.S.A. indicate that the level of iodine in the diet has increased and that the widespread use of this salt is unnecessary.
Varying amounts of sodium are added to food, but not always in the form of salt. Common food additives, such as baking soda, some preservatives, and monosodium glutamate (MSG), also contribute to the total amount of sodium we consume.
SALT AND HIGH BLOOD PRESSURE
Probably one-fifth of the population, because of genetic predisposition, may be increasing their risk of high blood pressure (hypertension) by having a high intake of sodium. People who have a high intake of sodium have a high incidence of hypertension and stroke. High blood pressure is rarely seen in those who consume less than 1.2 grams (1200 milligrams) of sodium per day. In Australia, on the other hand, where the sodium intake can be in the region of 4 to 8 grams per day, about one in five adult Australians has high blood pressure. Salt is not necessarily the only important factor leading to high blood pressure, but in some cases it is. There are sound reasons why Australians should reduce their sodium intake. But sodium is an essential nutrient, and we need a certain amount for normal body function. A safe intake is considered to be between 0.9 and 2.3 grams of sodium per day, although in special circumstances, such as excessive sweating and diarrhoea, higher levels may be needed.
There is usually no need to increase salt intake in hot climates to avoid cramps, fainting and other symptoms because the body's hormones will adjust over a few days and conserve body sodium. Excessive heat presents other risks and should, in any case, be avoided.
HOW CAN WE CONTROL OUR SALT INTAKE?
Some people find it hard to reduce their intake of sodium. We all have the ability to taste salt, but the extent to which we like our food salted can be modified by experience. The amount of salt we consume cannot be wholly controlled by the moderate use of the salt shaker at the dinner table. This use only accounts for about one-third of our daily intake. Up to half of our salt intake is from processed food, with the balance occurring naturally in food and water. The amount consumed in processed food is difficult to control, although with highly salted foods, taste is a reliable guide. Some items that do not taste highly salted can contribute significant quantities of sodium to our diet because of the amounts we consume. Examples include bread, tomato sauce, and cakes and biscuits. Many 'take-away' foods, such as fish and chips, hamburgers and Chinese food, are highly salted. Bottled mineral waters can contribute a significant amount of sodium. An indication of sodium content is usually given on the label.
An increase in potassium intake seems to offset the adverse effect that sodium has on blood pressure. Foods that contain significant amounts of potassium and also low levels of sodium are fresh and frozen fruits and vegetables. But there is no justification for the unrestricted use of potassium salts as substitutes for sodium, as this would present new problems. Potassium supplements and salt substitutes can be potentially hazardous to health and should only be used under medical supervision.
SODIUM INTAKE
Recommended daily dietary intake of sodium (Australia):
Infants: 6-25 millimoles 0.1-0.6 grams
Children: 14-100 millimoles 0.3-2.3 grams
Adults: 40-100 millimoles 0.9-2.3 grams
