Studies in animals have demonstrated that all require a high salt intake to develop high blood pressure. The higher the salt intake, the greater the rise in pressure. For instance, a study in chimpanzees (98.8% genetic homology with man) where one group was maintained on their normal diet of around half a gram of salt per day was compared with a randomly selected group that had salt intake increased to 10 to 15 grams per day over 20 months. There was a substantial rise in blood pressure in those chimpanzees on the high salt diet (1) (Fig 1).
Figure 1. Blood pressure in chimpanzees who either continued on their usual diet (0.5g salt/day) or on an increased salt intake (10-15 g salt/day). At the end of the 20-month study, the salt supplements were stopped and blood pressure declined to that of the control group. (Adapted from Ref. 1 ).
Human Genetic Studies
There are several very rare genetic causes of high blood pressure. All of these result in a reduction in the kidney's ability to excrete salt, and thereby cause high blood pressure. This is considerably aggravated if salt is consumed (2, 3). Rare genetic causes of low blood pressure have also been described. These result in the kidney being unable to hold on to salt normally, thereby causing low blood pressure. These forms of low blood pressure are ameliorated by high salt intake. Overall, these studies clearly indicate the importance of salt intake in regulating blood pressure in humans.