A Cochrane review [Abstract] 1 included 20 studies with a total of 3 512 normotensive subjects. 18 studies (n=3 140) were included in the meta-analysis. Included studies compared dietary calcium interventions such as supplementation (tablets in 17 studies) or food fortification (high-calcium skim milk in 1 study, and fortified juice in 2 studies) versus placebo or control with a median follow-up intervention period of 3.5 months. For most studies, the intervention was 1000 to 2000 mg of elemental calcium per day.
Calcium supplementation decreased systolic blood pressure (SBP; MD -1.37 mmHg, 95% CI -2.08 to -0.66; 18 studies, n=3 140) and diastolic blood pressure (DBP; MD -1.45 mmHg, 95% CI -2.23 to -0.67; 17 studies, n=3 039) compared with placebo. A dose-response effect trend was detected. Studies with interventions of 1500 mg of calcium a day or higher showed a higher decrease in SBP and DBP than studies with interventions less than 1000 mg a day. Studies performed in younger people tended to show higher reductions in systolic and diastolic blood pressure than those in older people. There was a greater effect in those studies lasting less than 6 months, and there was some suggestion that the effect might be lost over time in populations with adequate calcium intake, as some studies showed no effect after 30 months.
Another Cochrane review [Abstract] 2 included 13 studies with a total of 485 adults over 18 years of age with elevated blood pressure (a minimum of 140 mmHg for SBP or 85 mmHg for DBP). Calcium supplements with mean dose of 1.1g/day (range from 0.4 to 2 g/day) were compared to placebo (except in one study to no treatment) with a median duration of 8 weeks follow-up (range from 8 to 15 weeks). Combining all studies, participants receiving calcium supplementation had a statistically significant reduction in SBP (MD -2.5 mmHg, 95% CI -4.5 to -0.6), but not DBP (MD -0.8 mmHg, 95% CI -2.1 to 0.4) compared to control.
A meta-analysis of randomized controlled trials 3 included 40 studies with a total of 2 492 normotensive (27 studies) or hypertensive (23 studies) subjects. Calcium supplementation (mean daily dose 1200 mg) reduced SBP by -1.86 mm Hg (95% CI -2.91 to -0.81) and DBP by -0.99 mm Hg (95% CI -1.61 to -0.37). In people with a relatively low initial calcium intake (≤ 800 mg per day) the observed reduction was somewhat larger, -2.63 mmHg (95% CI -4.03 to -1.24) for SBP and -1.30 mmHg (95% CI -2.13 to -0.47) for DBP. Blood pressure responses to calcium supplementation did not differ significantly in strata of median age (<45 vs ≥45 years), calcium dose (≤1000 mg vs >1000 mg/day), initial BP (<140/90 vs ≥140/90 mm Hg) and gender (≤50 vs >50% males).
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