It's official: taking potassium supplements will lower your blood pressure if you have mild hypertension.

Although several medical studies have pointed to the beneficial effect of potassium and magnesium supplementation, a controlled trial at the University of Poona in India attempted to investigate whether potassium supplements, alone and in combination with magnesium, had any benefit to 37 patients with slightly elevated blood pressure.

The investigators found that blood pressure decreased dramatically with the potassium supplements, but that the magnesium had no additional benefit.
According to the authors, several mass epidemiological surveys have suggested that the less potassium a person has in his diet, the more likely he is to suffer from hypertension - hence why vegetarians whose diet is rich in potassium have a lower incidence of the disease than the population at large.

'Our results also suggest that treatment with potassium lowers serum cholesterol concentrations, which will be an added advantage,' they conclude. 'Hence, moderate daily supplements of potassium could be a valuable alternative to pharmacological methods for controlling mild hypertension, especially in those who are not willing or able to restrict salt intake.'-The British Medical journal, 15 September 1990.