The Blood Pressure Effects of Calcium Supplementation in Humans of Known Sodium Responsiveness

We examined the interactions between sodium and calcium responsiveness of blood pressure by studying the effects of calcium supplementation in 46 normotensive and hypertensive subjects who had been previously characterized as salt sensitive or salt resistant on the basis of their blood pressure responses to rapid sodium and extracellular volume expansion and contraction. The calcium supplementation study utilized a placebo-controlled, double-blind, randomized crossover design. Subjects received calcium carbonate supplementation (1.5 g/day) for 8 weeks or matching placebo, with 2-week placebo lead-in and crossover periods. For the entire group, no significant blood pressure changes were seen with calcium supplementation. When the subjects were separated on the basis of race or prior salt sensitivity, significant differences were seen. Blacks and salt sensitive subjects exhibited a significant (P < .05) blood pressure decrease when compared to their counterparts. Calcium sensitive subjects had significantly (P < .02) lower levels of plasma renin activity than those not demonstrating a decrease in blood pressure with added calcium. When urinary calcium excretion of subjects previously defined as salt sensitive or salt resistant were compared, the former had significantly (P < .001) higher calcium excretion values at baseline as well as during the placebo and calcium supplementation periods than did the latter. There were no known differences in dietary calcium intake to account for the striking urinary findings. These observations confirm the heterogeneity of blood pressure response to calcium supplementation and demonstrate congruity between sodium and calcium responsiveness of blood pressure in normal and hypertensive humans.(ABSTRACT TRUNCATED AT 250 WORDS)