ABC of Nutrition.

Correlation of blood pressure and salt intake is often not demonstrable between individuals VA I There are a few isolated communities in which hypertension is not seen, such as the Yanomamo Indians (in the Amazon), Kalahari Bushmen (Botswana), and remote Pacific islanders. These people have very low salt intakes, about 2 g salt per day or less. In northern Japan salt intakes are very high, 25 g salt per day, and there is a higher incidence of both hypertension and stroke than in the USA. Inability to show a consistent correlation between individual salt intake (most conveniently assessed by 24 hour urinary sodium excretion) and blood pressure is the major weakness of the salt hypothesis. Rats show genetic variations in sensitivity of blood pressure to salt intake and the same probably occurs in man. Correlation has been found in people with a family history of hypertension. There have been several reports that people with hypertension tend to have increased sodium concentrations in cells and abnormal activities in blood cell membranes of the several mechanisms for keeping sodium out of and potassium inside the cells. Diuretic drugs lower blood pressure by increasing urinary sodium excretion. Alternatively a sufficient reduction of dietary sodium can produce negative sodium balance. This requires (a) no salt added at table or in cooking; (b) restriction or omission of foods in which salt has been incorporated during processing; and (c) emphasis on foods at the lower end of the table. The physiological requirement for sodium is no more than 20 mmol Na per day, equivalent to about 1 g of salt (NaCl). Sodium loss through the skin is very small unless there is much sweating. But people on low sodium intakes and those who have adapted to hot climates lose less sodium in sweat, about 30 mmol/1. For the general adult population, mainly as a measure to reduce hypertension, the USA and Australia and the WHO Expert Committee on Prevention of Coronary Heart Disease (1981) recommend that people should not eat more than 6 g salt per day.