Magnesium for leg cramps…just as good as placebo?

Clinical question: does magnesium work for leg cramps?

Findings 1: Cochrane review, 2012

Both magnesium & placebo reduce the frequency of leg cramps with a non-significant difference between the two groups.  The Cochrane review analysed four RCTs (n=322), two of which were deemed to have a high risk of bias and the remaining two trials had a combined total of 86 participants – better quality evidence needed.

Findings 2: Roguin Moar et al. JAMA, 2017

A double-blind placebo-controlled RCT tried to put the issue to rest.  They again concluded that oral magnesium was no superior to placebo for adults with nocturnal leg cramps.  The trial included 94 participants randomised to magnesium oxide 865mg or placebo for four weeks.  Both the magnesium and placebo groups experienced a statistically significant reduction in leg cramps by approximately 3 cramps per week.  However the difference between the groups was not statistically significant (p = 0.67).  Unfortunately this study was under-powered, so if there was a difference between magnesium and placebo groups, the low participation rate resulted in difficulty detecting this.

Summary

The evidence available to help us answer this question is of low quality and further research would be welcome.  It seems that magnesium does work in reducing nocturnal leg cramps, but it’s effect is no better than that of placebo.

Practical implications?

This exercise has reinforced that modern medicine doesn’t always have the answers for everything. Despite this, given oral magnesium is well-tolerated by most and the risk of harm is low, it can provide real relief for some people with leg cramps (this is also irrespective of magnesium levels).  The question now is, how do I tell my patients that it’s no better than placebo?

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