Salt and hypertension.

Studies comparing different communities have suggested that the amount of salt in the diet may play an important role in determining blood pressure levels within a particular community. Intervention studies have also suggested that salt intake may play an important role in determining blood pressure levels in man. In animals, where more clearcut experiments can be done, an increase in salt intake both in inherited forms of hypertension and experimental hypertension causes a further rise in blood pressure. Recent work has suggested that this rise in blood pressure could be related to an inherited or imposed defect in the kidney's ability to excrete sodium, which will give rise to greater compensatory mechanisms to overcome the sodium retention. These compensatory mechanisms might eventually be responsible for the development of high blood pressure. In patients who have already developed high blood pressure, restricting the amount of salt in the diet does cause a fall in blood pressure in many patients. However, short-term reduction of salt intake in normotensive subjects causes little, if any, fall in blood pressure. The effectiveness of short term salt restriction in lowering blood pressure in adults therefore appears to be related to the severity of the high blood pressure and, probably more directly, to the suppression of the renin system that occurs as blood pressure rises.