CALCIUM
Calcium is more likely to lower blood pressure in hypertensive individuals consuming a -.u-salt intake, further suggesting a link between sodium and potassium intake in their effects blood pressure. The amount of potassium intake required for optimal reduction in blood ssure in those who are sensitive to this mineral is not clear. Most studies indicate that . a.ary potassium defi-::iency begins at levels of intake 50 mmol/d and is clearly observed at :akes of 30 mmol/d or less.
Dietary sources of potassium are largely fresh fruits and vegetables. In environments here these are scarce, e.g., because of cold climate or high cost, potassium deficiency is ore likely. Among a group of normotensive nurses in whom dietaiy intakes of potassium, :alcium, and magnesium were defiCient, only potassium supplementation reduced blood pressure. 3ecent studies using diets involving multiple mineral manipulations, such as the Dietary Approaches Stop Hypertension (DASH) Trial are discussed in the Combination Diets section.
Epidemiological surveys have suggested a relationship between reduced dietary calcium take and hypertension. Several studies have demonstrated a small and inconsistent effect f calcium supplementation to lower blood pressure. Again, this appears to be largely owing to the heterogeneity in human responses to calcium supplementation. Subgroup analyses of some of the larger studies suggest that those in whom dietary calcium intake is often reduced
African-Americans, the elderly) are more likely to demonstrate a reduction in blood pressure with calcium supplementation than other groups in whom intake is higher. Since both subgroups are traditionally salt sensitive, we conducted a study of calcium supplementation in a group of normal and hypertensive subjects who had been previously categorized with respect to salt sensitivity of blood pressure. We found no significant effect of calcium supplementation on blood pressure for the entire group.
However, when the subjects were separated on the basis of salt-sensitivity status, we found a significant decrease in blood pressure when the salt-sensitive subjects received calcium supplements and a significant increase in blood pressure when calcium was given to the saltresistant subjects. These findings suggested a reciprocal relationship between the effects of calcium and sodium on blood pressure that was confirmed by the results of the DASH Trial.
