The influence of dietary and nondietary calcium supplementation on blood pressure - An updated metaanalysis of randomized controlled trials

We updated our previous systematic review of the effect of supplemental cal cium on blood pressure. We extended our previous searches on MEDLINE and EM BASE to May 1997 and examined citations from relevant articles. We contacte d the authors of eligible trials to ensure the accuracy and completeness of data, and to identify unpublished trials. We included any study in which i nvestigators randomized hypertensive or normotensive people to calcium supp lementation or alternative therapy and measured blood pressure for at least 2 weeks. In addition to 32 trials included in the prior metaanalysis, 10 n ew trials contributed to this metaanalysis. Two pairs of independent review ers abstracted data and assessed the validity of the study data according t o six quality criteria. We calculated the differences in blood pressure cha nge between the calcium supplementation and control groups and pooled the e stimates with each trial weighted with the inverse of the variance using a random effects model. The predictors of blood pressure reduction that we ex amined included method of supplementation, baseline blood pressure, and the methodologic quality of the studies. The pooled analysis shows a reduction in systolic blood pressure of -1.44 m m Hg (95% confidence interval -2.20 to -0.68; P < .001) and in diastolic bl ood pressure of -0.84 mm Hg (95% confidence interval -1.44 to -0.24; P < .0 01). We found statistically significant heterogeneity of results across tri als (P less than or equal to .02), which persisted when we looked at the no ndietary trials alone, but not when we restricted our analysis to dietary t rials. Although there was a trend toward larger effects with dietary interv entions, none of the possible mediators of blood pressure reduction explain ed differences in treatment effect. We conclude that calcium supplementation leads to a small reduction in syst olic and diastolic blood pressure. The effect of supplemental calcium in th e diet is at least as great as nondietary supplementation. (C) 1999 America n Journal of Hypertension, Ltd.