EFFECTS OF DIETARY CALCIUM SUPPLEMENTATION ON BLOOD-PRESSURE - A METAANALYSIS OF RANDOMIZED CONTROLLED TRIALS

Objective.-To review the effect of supplemental calcium on blood press ure. Data Source. We searched MEDLINE and EMBASE for 1966 to May 1994. We contacted authors of eligible trials to ensure accuracy and comple teness of data and to identify unpublished trials. Study Selection.-We included any study in which investigators randomized people to calciu m supplementation or placebo and measured blood pressure for at least 2 weeks. Fifty-six articles met the inclusion criteria, and 33 were el igible for analysis, involving a total of 2412 patients. Data Extracti on.-Two pairs of independent reviewers abstracted data and assessed va lidity according to six quality criteria. Data Synthesis.-We calculate d the differences in blood pressure change between the calcium supplem entation group and the control group and pooled the estimates, with ea ch trial weighted with the inverse of the variance using a random-effe cts model, Predictors of blood pressure reduction that we examined inc luded method of supplementation, baseline blood pressure, and the meth odological quality of the studies. The pooled analysis showed a reduct ion in systolic blood pressure of -1.27 mm Hg (95% confidence interval [CI], -2.25 to -0.29 mm Hg; P=.01) and in diastolic blood pressure of -0.24 mm Hg (95% CI, -0.92 to 0.44 mm Hg; P=.49). None of the possibl e mediators of blood pressure reduction explained differences in treat ment effects. Conclusions.-Calcium supplementation may lead to a small reduction in systolic but not diastolic blood pressure. The results d o not exclude a larger, important effect of calcium on blood pressure in subpopulations. In particular, further studies should address the h ypothesis that inadequate calcium intake is associated with increased blood pressure that can be corrected with calcium supplementation.