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Studies offer conflicting findings on magnesium's effect on BP
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A randomized controlled trial found no significant effect of magnesium on BP, but a meta-analysis of other trials showed a modest effect of magnesium supplementation on BP.
The randomized trial was published in The American Journal of Cardiology and the meta-analysis was published in Hypertension.
Potassium vs. magnesium
Wanpen Vongpatanasin, MD, from the department of internal medicine, cardiology division/hypertension section and Charles and Jane Pak Center for Mineral Metabolism and Clinical Research at University of Texas Southwestern Medical Center, Dallas, and colleagues designed a randomized, double blind, placebo-controlled crossover study to compare the effects of potassium-magnesium citrate, potassium chloride and potassium citrate on 24-hour ambulatory BP and urinary 8-isoprostane, a marker of oxidative stress, in patients with hypertension and prehypertension.
Wanpen Vongpatanasin
Thirty patients with prehypertension (n = 6) or stage I hypertension (n = 24) were enrolled in the study. All patients (mean age, 54 years; 53% women; 40% black) had systolic BP between 120 mm Hg and 159 mm Hg and diastolic BP between 80 mm Hg and 99 mm Hg.
During the four-phase study, patients received one of the study drugs for 4 weeks with at least 1 week of washout between a placebo phase, a potassium chloride phase (40 mEq powder/day), a potassium citrate phase (40 mEq powder/day diluted in water) and a potassium-magnesium citrate phase (40 mEq potassium, 20 mEq magnesium and 74 mEq citrate powder/day).
According to the results, potassium chloride reduced nighttime systolic BP compared with placebo (116 mm Hg vs. 121 mm Hg; P < .01). Potassium-magnesium citrate did not have a significant effect on BP (118 mm Hg vs. 119 mm Hg for placebo) but reduced urinary 8-isoprostane compared with placebo (13.5 ng/mgCr vs. 21.1 ng/mgCr; P < .001). Potassium chloride (21.4 ng/mgCr) and potassium citrate (18.3 ng/mgCr) had no effect on urinary 8-isoprostane compared with placebo (P > .1 for both).
“More studies are needed to determine long-term effects of [potassium-magnesium citrate] on exercise capacity, insulin sensitivity and [CV] outcomes in hypertensive patients,” Vongpatanasin and colleagues wrote.
A modest effect
Yiqing Song, MD, ScD, associate professor in the department of epidemiology at the Richard M. Fairbanks School of Public Health at Indiana University, Indianapolis, and colleagues conducted a meta-analysis of 34 randomized controlled trials that tested the BP-lowering effects of oral magnesium supplementation and found that magnesium had a modest effect on BP.
Yiqing Song
The studies, conducted in the United States, Asia, Europe and Latin America, included 2,028 normotensive or hypertensive patients (55% women).
Song and colleagues wrote that magnesium supplementation (median dose, 368 mg/day) for a median duration of 3 months was associated with reduction in systolic BP (weighted mean difference, 2 mm Hg; 95% CI, 0.43-3.58) and diastolic BP (weighted mean difference, 1.78 mm Hg; 95% CI, 0.73-2.82). Systolic and diastolic BP responses differed slightly in dose- and duration-dependent manners across the studies.
Serum magnesium levels increased by 0.05 mmol/L (95% CI, 0.03-0.07) in those assigned magnesium compared with those assigned placebo. Magnesium supplementation with a 300 mg per day dose or duration of 1 month elevated serum magnesium and reduced BP, and serum magnesium was negatively associated with diastolic BP but not systolic BP (P < .05), the researchers wrote.
“With its relative safety and low cost, magnesium supplements could be considered as an option for lowering [BP] in high-risk persons or hypertension patients,” Song said in a press release. “Consistent with previous studies, our evidence suggests that the anti-hypertensive effect of magnesium might be only effective among people with magnesium deficiency or insufficiency. Such suggestive evidence indicates that maintenance of optimal magnesium status in the human body may help prevent or treat hypertension.”
Penny Kris-Etherton, PhD, an American Heart Association spokeswoman and distinguished professor of nutrition at the Penn State University, said, however, that magnesium supplements are not necessary.
“This study underscores the importance of consuming a healthy diet that provides the recommended amount of magnesium as a strategy for helping to control [BP],” Kris-Etherton said in the release. “Importantly, this amount of magnesium (368 mg/day) can be obtained from a healthy diet that is consistent with AHA dietary recommendations.” – by Tracey Romero
Disclosure: The researchers for both studies and Kris-Etherton report no relevant financial disclosures.
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