Preliminary report: natriuretic effect of calcium supplementation in hypertensive women over forty.

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Abstract
Twenty-four hypertensive women over 40 years of age were given calcium carbonate 1 g/d for 12 weeks after a 4-week period of observation. Blood pressures were measured every 2 weeks. Plasma ionized calcium (Ca++), sodium (Na), and potassium (K) were measured twice in the control period and twice in the Ca-supplementation period. Urine measurements included Ca, Magnesium (Mg), Na, K, prostaglandin E2, and osmolality. Blood pressures were averaged to get group means, and these were compared using the paired t-test. For the group, seated systolic blood pressure fell from 141.5 +/− 13.2 to 136.3 +/− 11.4 mm Hg (p less than 0.025) at the end of 12 weeks of supplementation, and diastolic blood pressure fell from 84.5 +/− 7.5 to 81.1 +/− 7.1 mm Hg (p less than 0.025). There was no correlation between serum Ca++ and blood pressure. The urinary Na excretion was markedly elevated during the Ca supplementation period: 25.8 +/− 14.2 vs. 18.4 +/− 7.9 mmol/4 hr (p less than 0.005). These results suggest an indirect (natriuretic) effect as the means by which Ca supplementation lowers blood pressure.