Dr. Lindsy Kass and colleagues at the University of Hertfordshire, UK, reported in the European Journal of Clinical Nutrition, that supplementation yielded net pressure reductions of 3-4 mmHg systolic, and 2-3 mmHg diastolic on average. Duration of treatment in the various trials ranged from 3-24 weeks, with a mean of 11 weeks.
The effects were dose-dependent, with the largest responses seen in subjects taking 370 mg/day or more. The pressure reductions were statistically and clinically significant. Effects of the size observed in this analysis are deemed meaningful in terms of CVD risk reduction when seen in antihypertensive drug studies.
Subjects in the various trials comprising Dr. Kass' analysis were from 12 different countries in Europe, Asia, North & South America, and had baseline pressures in the ranges of 110-173 mmHg systolic, and 73-106.5 diastolic, representing a spectrum from normotensive to fully hypertensive. The investigators found no geographically-associated variation in the patterns of BP reduction.
The notion that magnesium may have a role in managing hypertension emerged from epidemiological observations of an inverse relationship between magnesium intake and prevalence of hypertension, and from recognition that this mineral induces vasorelaxation. Several studies have shown consistent pressure-lowering effects among normotensive people taking supplemental magnesium, but previous metanalyses of data from hypertensive patients, including a 2006 review by the Cochrane Collaboration, were inconclusive.
The authors of the current metanalysis took into account the fact that different forms of supplemental magnesium contain different amounts of elemental magnesium. They adjusted for this in their dose calculations prior to determining the effect sizes. Only one of the 22 studies included in the analysis provided data on serum magnesium levels.
"It would also have been beneficial if trials had looked at pre-trial serum magnesium levels and then looked at this again after supplementation; this would also have given a better understanding of absorption over a range of magnesium intakes," said Dr. Kass in the report.
Thirteen of the 22 trials reported adverse effects associated with higher levels of magnesium intake. However, for the vast majority of patients these were not serious, consisting of the expected mild diarrhea and GI discomfort.
Dr. Kass and colleagues believe these new data should prompt a re-assessment of magnesium for preventing or treating hypertension, and by extension, cardiovascular disease in general. "Magnesium as a supplement has been shown to decrease BP in normotensives, yet is rarely considered as a supplement for elevated BP."
The authors hope this will change, as more clinicians realize the potential of this low-cost and ubiquitous supplement which has a host of other cardiovascular, neurologic, and musculoskeletal benefits.
"Although these (pressure) reductions are small, they could have a significant effect on BP, particularly on the pre-hypertensive population group."