Magnesium supplementation for the management of primary hypertension in adults

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Abstract
Background Epidemiological evidence on the effects of magnesium on blood pressure is inconsistent. Metabolic and experimental studies suggest that magnesium may have a role in the regulation of blood pressure. Objectives To evaluate the effects of magnesium supplementation as treatment for primary hypertension in adults. Search methods 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. Selection criteria Inclusion criteria were: 1) RCTs of a parallel or crossover design comparing oral magnesium supplementation 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; 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 magnesium supplementation was combined with other interventions. Data collection and analysis Two reviewers independently abstracted 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 Twelve RCTs (n=545) with eight to 26 weeks follow‐up met our inclusion criteria. The results of the individual trials were heterogeneous. Combining all trials, participants receiving magnesium supplements as compared to control did not significantly reduce SBP (mean difference: ‐1.3 mmHg, 95% CI: ‐4.0 to 1.5, I2=67%), but did statistically significantly reduce DBP (mean difference: ‐2.2 mmHg, 95% CI: ‐3.4 to ‐0.9, I2=47%). Sensitivity analyses excluding poor quality trials yielded similar results. Sub‐group analyses and meta‐regression indicated that heterogeneity between trials could not be explained by dose of magnesium, baseline blood pressure or the proportion of males among the participants. Authors' conclusions In view of the poor quality of included trials and the heterogeneity between trials, the evidence in favour of a causal association between magnesium supplementation and blood pressure reduction is weak and is probably due to bias. This is because poor quality studies generally tend to over‐estimate the effects of treatment. Larger, longer duration and better quality double‐blind placebo controlled trials are needed to assess the effect of magnesium supplementation on blood pressure and cardiovascular outcomes.