Elevated blood pressure (BP) or hypertension can lead to cardiovascular disease, stroke and renal disease. Epidemiological studies suggest that changing the dietary levels of calcium, potassium, magnesium or sodium can affect BP in some people. This systematic review focuses on the effects of concurrently attempting to change any combination of calcium, magnesium, or potassium levels in the diet of adults with primary hypertension.
This review found no robust evidence to suggest that combinations of potassium, calcium or magnesium can reduce high blood pressure (BP) in adults. Only three trials assessing a total of 277 participants were found. The only combination assessed by all three trials was potassium and magnesium, demonstrating a statistically non-significant reduction in BP among people receiving this combination. One trial assessed both calcium & magnesium and calcium & potassium and found that neither combination had very much effect on BP. None of the trials were of high quality, so their results may not be reliable. Very few mild adverse effects were reported. These were of short duration and participants did not have to stop taking their treatment.
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.
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.
To evaluate the effects of combined mineral supplementation as a treatment for primary hypertension in adults.
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.
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.
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.
We included three RCTs (n=277) with 24-28 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 potassium-magnesium combination. None of the trials provided mortality or morbidity data. The potassium-magnesium combination 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 (I2=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.