This review examines whether taking potassium supplements can be recommended for treating adults with high blood pressure from no known cause. The results of the trials varied a lot: some trials found potassium lowered blood pressure much more than a dummy drug (placebo), while others found little difference between potassium and placebo. Overall no significant reduction in blood pressure from taking potassium supplements was found.
Most included trials were of poor quality, so their results may not be reliable. The trials were not long enough or large enough to measure whether potassium supplements reduce the risk of death, heart attack or stroke, which may be caused by high blood pressure. The studies reporting adverse effects did not find any serious side effects from taking potassium supplements.
This review does not confirm whether potassium supplements can lower high blood pressure and therefore does not recommend them for treating hypertension. More trials enrolling a large number of participants with long periods of follow-up are necessary to know whether or not potassium supplements can lower high blood pressure.
Potassium supplementation has no statistically significant effect on blood pressure. Due to small number of participants in the two high quality trials, the short duration of follow-up, and the unexplained heterogeneity between trials, the evidence about the effect of potassium supplementation on blood pressure is not conclusive. Further high quality RCTs of longer duration are required to clarify whether potassium supplementation can reduce blood pressure and improve health outcomes.
Epidemiological evidence on the effects of potassium on blood pressure is inconsistent.
To evaluate the effects of potassium supplementation on health outcomes and blood pressure in people with elevated blood pressure.
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.
Inclusion criteria were: 1) RCTs of a parallel or crossover design comparing oral potassium supplements with placebo, no treatment, or usual care; 2) treatment and follow-up >=8 weeks; 3) participants over 18 years, with raised systolic blood pressure (SBP) >=140 mmHg or diastolic blood pressure (DBP) >=85 mmHg); 4) SBP and DBP reported at end of follow-up. We excluded trials where: participants were pregnant; received antihypertensive medication which changed during the study; or potassium supplementation was combined with other interventions.
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.
Six RCT's (n=483), with 8-16 weeks follow-up, met our inclusion criteria. Meta-analysis of five trials (n=425) with adequate data indicated that potassium supplementation compared to control resulted in a large but statistically non-significant reductions in SBP (mean difference: -11.2, 95% CI: -25.2 to 2.7) and DBP (mean difference: -5.0, 95% CI: -12.5 to 2.4). The substantial heterogeneity between trials was not explained by potassium dose, quality of trials or baseline blood pressure.
Excluding one trial in an African population with very high baseline blood pressure resulted in smaller overall reductions in blood pressure (SBP mean difference: -3.9, 95% CI: -8.6 to 0.8; DBP mean difference: -1.5, 95% CI: -6.2 to 3.1). Further sensitivity analysis restricted to two high quality trials (n=138) also found non-significant reductions in blood pressure (SBP mean difference: -7.1, 95% CI: -19.9 to 5.7; DBP mean difference: -5.5, 95% CI: -14.5 to 3.5).