Effect of transdermal magnesium cream on serum and urinary magnesium levels in humans: A pilot study.

BACKGROUND: Oral magnesium supplementation is commonly used to support a low magnesium diet. This investigation set out to determine whether magnesium in a cream could be absorbed transdermally in humans to improve magnesium status. METHODS AND FINDINGS: In this single blind, parallel designed pilot study, n = 25 participants (aged 34.3+/-14.8y, height 171.5+/-11cm, weight 75.9 +/-14 Kg) were randomly assigned to either a 56mg/day magnesium cream or placebo cream group for two weeks. Magnesium serum and 24hour urinary excretion were measured at baseline and at 14 days intervention. Food diaries were recorded for 8 days during this period. Mg test and placebo groups' serum and urinary Mg did not differ at baseline. After the Mg2+ cream intervention there was a clinically relevant increase in serum magnesium (0.82 to 0.89 mmol/l,p = 0.29) that was not seen in the placebo group (0.77 to 0.79 mmol/L), but was only statistically significant (p = 0.02)) in a subgroup of non-athletes. Magnesium urinary excretion increased from baseline slightly in the Mg2+ group but with no statistical significance (p = 0.48). The Mg2+ group showed an 8.54% increase in serum Mg2+ and a 9.1% increase in urinary Mg2+ while these figures for the placebo group were smaller, i.e. +2.6% for serum Mg2+ and -32% for urinary Mg2+. In the placebo group, both serum and urine concentrations showed no statistically significant change after the application of the placebo cream. CONCLUSION: No previous studies have looked at transdermal absorbency of Mg2+ in human subjects. In this pilot study, transdermal delivery of 56 mg Mg/day (a low dose compared with commercial transdermal Mg2+ products available) showed a larger percentage rise in both serum and urinary markers from pre to post intervention compared with subjects using the placebo cream, but statistical significance was achieved only for serum Mg2+ in a subgroup of non-athletes. Future studies should look at higher dosage of magnesium cream for longer durations. TRIAL REGISTRATION: ISRCTN registry ID No. ISRTN15136969.

Oral magnesium supplements decrease high blood pressure (SBP>155 mmHg) in hypertensive subjects on anti-hypertensive medications: a targeted meta-analysis.

Previously, we examined 44 human studies involving oral magnesium (Mg) supplementation for hypertension (HT), sorting them according to HT status, Mg dose and anti-hypertensive medication usage. We found that while some studies reported a significant lowering of blood pressure with Mg supplementation, others did not. We present here our first meta-analysis of a uniform subset from this series of studies. Seven studies, involving 135 hypertensive subjects on anti-hypertensive medication continuously for at least six months, with no more than a two-week washout and with a mean starting systolic blood pressure (SBP)>155 mmHg, demonstrated a mean change of -18.7 mmHg [95% CI=-14.95 to -22.45] p<0.0001 and an effect size test (Cohen's d)=1.19, i.e. a large and highly significant effect. Meta-analysis of diastolic blood pressure (DBP) for these same seven studies showed a mean change in DBP of -10.9 mmHg [95% CI=-8.73 to -13.1], p<0.0001, with an effect size test (Cohen's d)=1.19. Other studies from our original collection, approaching, but not meeting the >155 mmHg starting SBP values or not complying as regards anti-hypertensive medication usage, showed mean changes in both SBP and DBP with oral Mg that, while not approaching the high-responder values of the present study, appeared to include some high-responder subjects combined with low- or non-responder subjects. This uniform subset of seven studies showed a strong effect of Mg treatment in hypertension, which is in stark contrast to results of three other meta-analyses. Using non-uniform sets of studies, the small effects reported in previous meta-analyses may reflect a blending of dissimilar studies, which acted to seriously underestimate the potential of Mg in hypertension in some (but not all) subjects. Within studies, blending of non-, moderate and highresponder subjects in any one study might mask strong effects of Mg treatment in some subjects.