Effects of calcium plus vitamin D supplementation on blood pressure: a systematic review and meta-analysis of randomized controlled trials
The effect of calcium or vitamin D supplement on blood pressure (BP) has been explored in previous meta-analyses, but the results are conflicting. The combined efficacy of calcium and vitamin D on BP has not been systematically assessed. Thus, we conducted a meta-analysis of randomized controlled trials (RCTs) to explore the effect of calcium plus vitamin D (CaD) supplementation on changes of systolic blood pressure (SBP) and diastolic blood pressure among male and female participants (with and without diagnosed hypertension) aged 18 years or older. The PubMed, the Embase and the Cochrane Central Register of controlled trials were searched. A random effects model was used to calculate the pooled weighted mean differences (WMDs) with 95% confidence intervals (CIs) for the continuous outcome data. Cochrane Collaboration tool was used to assess the study quality of each trial. We further performed subgroup analysis and meta-regression by ethnicity, gender, age, health status, supplement dose, co-interventions, supplement duration and quality assessment. Eight RCTs involving 36 806 participants were assessed. The followup time ranged from 15 weeks to a maximum of 7 years. No meaningful effect on daytime office BP was detected in the present study, with evidence of significant heterogeneity. Subgroup analysis by gender indicated some evidence of elevated SBP in male participants, and the WMD (95% CI) was 1.49 mm Hg (1.03, 1.95). Further high-quality research is still warranted to confirm the magnitude of the effect of CaD supplementation on the changes of BP among participants with different ethnicity, gender, health status and CaD supplements.