Kass L, Weekes J, Carpenter L. Effect of magnesium supplementation on blood pressure: a meta-analysis. Eur J Clin Nutr. 2012 Feb 8. doi: 10.1038/ejcn.2012.4. [Epub ahead of print]
Meta-analysis. Of the 141 papers identified, only 22 trials with 23 sets of data (N=1,173), with 3 to 24 weeks of follow-up met the inclusion criteria, with a supplemented elemental magnesium range of 120–973 mg (mean dose 410 mg).
There was greater blood pressure reduction in crossover trials, which means when people with high blood pressure were not on magnesium, their blood pressure was higher; when they were on magnesium their blood pressure was lower. Also, the higher the magnesium dosage, the lower the blood pressure. Combining all trials showed a decrease in systolic blood pressure (SBP) of 3–4 mmHg and diastolic blood pressure (DBP) of 2–3 mmHg, which further increased with crossover-designed trials and intake >370 mg/day. The authors concluded that magnesium supplementation appears to achieve a small but clinically significant reduction in BP. They called for more studies.
The main take-home message from this meta-analysis is that magnesium does reduce blood pressure.
We have to remember that meta-analysis homogenizes all available information into a big blender and comes out with a number that is not necessarily the final answer to the study’s question. In the words of the authors, “This meta-analysis was conducted to assess the effect of magnesium supplementation on [blood pressure] and to establish the characteristics of trials showing the largest effect size.”
The authors found that the higher the amount of magnesium, over 370 mg/day, the greater the reduction in BP. None of the 22 studies chosen calculated the dietary intake of the subjects. The subjects were from 12 different countries, so we have no way of knowing if any of them were magnesium-deficient to begin with. There are many other variables in such an analysis, but in spite of all the drawbacks we should remember the conclusion and build on that result.
For example, clinically a dose of 370 mg of elemental magnesium is barely at the RDA, a level that prevents clinical magnesium deficiency symptoms. Magnesium given therapeutically is usually at a higher dose.
From this study you will be able to tell your patients that magnesium has been proven in numerous clinical trials to cause lowering of the blood pressure.
In the Magnesium Miracle I wrote, “Twenty-five years of research shows that under ideal conditions approximately 300 mg of magnesium is required merely to offset the daily losses. Since at best the body is actually absorbing only half of what is taken in, researchers feel that most people would benefit from magnesium supplementation. Otherwise, body tissue must be broken down to supply vital areas of the body with essential magnesium.1,2
“If you are under mild to moderate stress caused by a physical or psychological disease, physical injury, athletic exertion, or emotional upheaval, your requirements for magnesium increase from 6 mg/kg/day up to 10 mg/kg/day.3,4 Exposure to fluoride in water or dental products,5 a high protein diet,6 alcohol,7,8 high doses of Vitamin D,9 and B1210 increase the demand for magnesium. An average good diet may supply about 120 mg of magnesium per 1,000 calories, for an estimated daily intake of about 250 mg.”11,12
From this study you will be able to tell your patients that magnesium has been proven in numerous clinical trials to cause lowering of the blood pressure. And long with other lifestyle interventions, diet changes, and supplements, patients can often avoid antihypertensive medications, which can, themselves, cause magnesium deficiency.