Does regular use of magnesium oxide prevent nocturnal leg cramps?

Magnesium, in the short term at least, will decrease leg cramps by almost half in people who experience them regularly. However, so will placebo. Since the number of effective treatments for leg cramps is exactly zero, exploiting the placebo effect of magnesium seems to be a reasonable option, given the low likelihood of adverse effects from treatment. Don't shake your head: Placebo, even when patients are told they are receiving placebo, has been shown to work for low back pain and irritable bowel syndrome. We may be able to boost the placebo effect by explaining that the placebo has a powerful effect and insisting that it be taken faithfully every night. (LOE = 1b)

Roguin Maor N, Alperin M, Shturman E, et al. Effect of magnesium oxide supplementation on nocturnal leg cramps: a randomized clinical trial. JAMA Intern Med 2017;177(5):617-623.  [PMID:28241153]

Randomized controlled trial (double-blinded)

Industry

Concealed

Outpatient (any)

These investigators enrolled 94 patients, average age 65 years, with a history of nocturnal leg cramps. The patients all experienced at least 4 episodes of cramps during a 2-week run-in period (an average of approximately 8 per week). The patients were randomly assigned, using concealed allocation, to receive either placebo or a magnesium oxide preparation (providing 520 mg elemental magnesium) to be taken once daily at bedtime. Using intention-to-treat analysis, both groups experienced a drop by almost half in the number of weekly episodes, from 7.84 to 4.44 per week with magnesium treatment and from 8.51 to 5.48 per week with placebo. The difference was not significant between the groups. Similarly, there was no differences in the severity and duration of leg cramps, quality of life, or quality of sleep. The study was underpowered to find a decrease of 1 episode per week. Other studies have also failed to find a benefit of magnesium over placebo (Cochrane Database Syst Rev 2012 Sep 12;(9):CD009402).