Combined calcium, magnesium and potassium supplementation for the management of primary hypertension in adults.

BACKGROUND

Previous research suggests that increasing dietary intakes of calcium, potassium or magnesium separately may reduce BP to a small degree over the short term. It is unclear whether increasing intakes of a combination of these minerals produces a larger reduction in BP.

OBJECTIVES

To evaluate the effects of combined mineral supplementation as a treatment for primary hypertension in adults.

SEARCH STRATEGY

We searched the Cochrane Library, MEDLINE, EMBASE, Science Citation Index, ISI Proceedings, ClinicalTrials.gov, Current Controlled Trials, CAB abstracts, and reference lists of systematic reviews, meta-analyses and randomised controlled trials (RCTs) included in the review. The search was unrestricted by language or publication status.

SELECTION CRITERIA

Inclusion criteria were: 1) RCTs of a parallel or crossover design comparing oral supplements comprising a combination of potassium, and/or calcium, and/or magnesium with placebo, no treatment, or usual care; 2) treatment and follow-up >=8 weeks; 3) participants over 18 years old, with raised systolic blood pressure (SBP) >=140 mmHg or diastolic blood pressure (DBP) >=85 mmHg with no known primary cause; 4) SBP and DBP reported at end of follow-up. We excluded trials where participants were pregnant, or received antihypertensive medication which changed during the study.

DATA COLLECTION AND ANALYSIS

Two reviewers independently extracted data and assessed trial quality. Disagreements were resolved by discussion or a third reviewer. Random effects meta-analyses and sensitivity analyses were conducted.

MAIN RESULTS

We included three RCTs (n=277) with between 24 and 28 weeks follow-up. Three combinations of minerals were investigated: potassium & magnesium, calcium & magnesium, and calcium & potassium. One trial investigated combinations of calcium & magnesium and of calcium & potassium, and for each found a statistically non-significant increase in both SBP and DBP. All three trials investigated the combination of potassium & magnesium. None of the trials provided data on mortality or morbidity. The combination of potassium & magnesium compared to control resulted in statistically non-significant reductions in both SBP (mean difference = -4.6 mmHg, 95% CI: -9.9 to 0.7) and DBP (mean difference = -3.8 mmHg, 95% CI: -9.5 to 1.8), although the results were heterogeneous (I(2)=68% and 85% for SBP and DBP respectively).A sensitivity analysis using alternative reported values which accounted for missing data had very little effect on DBP but resulted in a larger, statistically significant reduction in SBP (mean difference = -5.8 mmHg, 95% CI: -10.5 to -1.0). The quality of the trials was not well reported.

AUTHORS' CONCLUSIONS: We found no robust evidence that supplements of any combination of potassium, magnesium or calcium reduce mortality, morbidity or BP in adults. More trials are needed to investigate whether the combination of potassium & magnesium is effective.