DIETARY CALCIUM, CALCIUM SUPPLEMENTATION, AND BLOOD-PRESSURE IN AFRICAN-AMERICAN ADOLESCENTS

Background: Intake of calcium from the diet is inversely associated wi th blood pressure in observational studies and animal models but rando mized trials in humans have found only small effects of calcium supple mentation on blood pressure. A blood pressure-lowering effect of calci um supplementation may thus be restricted to persons with a low intake of calcium from the diet and specific genetic or other characteristic s. Objective: A randomized trial was conducted to assess the effect of calcium supplementation on blood pressure in African American adolesc ents. Rapid growth during adolescence may increase calcium requirement s, and avoidance of milk and milk products by some African Americans c an result in low intake of calcium.Design: One hundred sixteen adolesc ents (65 girls, 51 boys; mean age: 15.8 y) were given calcium (1.5 g/d ) or placebo for 8 wk in a randomized, double-blind, crossover design. Blood pressure was measured after 2, 4, and 8 wk. Dietary calcium was determined with a validated food-frequency questionnaire. Results: Th e net effect (+/-SE) of calcium supplementation on diastolic blood pre ssure was a reduction of 1.9 +/- 1.1 mm Hg (P = 0.04, one-tailed t tes t). Blood pressure reduction was greater in adolescents with lower int ake of calcium from the diet (P = 0.003, one-tailed t test for interac tion): -4.9 +/- 1.6, -2.3 +/- 1.6, and 1.4 +/- 1.8 mm Hg for change in the lower (0.024-0.067 g Ca/MJ), middle (0.069-0.091 g Ca/MJ), and up per (0.093-0.217 g Ca/MJ) tertiles, respectively. No main effect on sy stolic blood pressure was detected. Conclusion: These findings suggest that calcium supplementation may lower diastolic blood pressure in Af rican American adolescents with low dietary intakes of calcium.