Effect of calcium and vitamin D supplementation on blood pressure: the Women's Health Initiative Randomized Trial

Abstract

Experimental and epidemiological studies suggest that calcium and vitamin D supplements may lower blood pressure. We examined the effect of calcium plus vitamin D supplementation on blood pressure and the incidence of hypertension in postmenopausal women. The Women's Health Initiative Calcium/Vitamin D Trial randomly assigned 36 282 postmenopausal women to receive 1000 mg of elemental calcium plus 400 IU of vitamin D3 daily or placebo in a double-blind fashion. Change in blood pressure and the incidence of hypertension were ascertained. Over a median follow-up time of 7 years, there was no significant difference in the mean change over time in systolic blood pressure (0.22 mm Hg; 95% CI: -0.05 to 0.49 mm Hg) and diastolic blood pressure (0.11 mm Hg; 95% CI: -0.04 to 0.27 mm Hg) between the active and placebo treatment groups. This null result was robust in analyses accounting for nonadherence to study pills and in baseline subgroups of interest, including black subjects and women with hypertension or high levels of blood pressure, with low intakes of calcium and vitamin D or low serum levels of vitamin D. In 17 122 nonhypertensive participants at baseline, the hazard ratio for incident hypertension associated with calcium/vitamin D treatment was 1.01 (95% CI: 0.96 to 1.06.) In postmenopausal women, calcium plus vitamin D3 supplementation did not reduce either blood pressure or the risk of developing hypertension over 7 years of follow-up.

Figure 1

Systolic blood pressure change (A) and diastolic blood pressure change (B) by calcium/vitamin D treatment assignment in 36,189 participants with measured blood pressure at randomization. R indicates randomization into the trial. P-values are for main effect of randomization assignment.

Figure 2

Effect of Calcium and Vitamin D assignment on risk of developing hypertension in 17,122 participants without hypertension during an average of 7 years follow-up, overall and by baseline subgroups. Hypertension defined as first self-report of medication prescribed for hypertension or BP of ≥ 140/90. (see attached PDF)