A Cochrane review included 6 trials involving a total of 390 women. Magnesium (taken orally for 2 to 4 weeks) did not consistently reduce the frequency of leg cramps compared with placebo or no treatment (4 trials): frequency of leg cramps after treatment: never, and twice a week (RR 5.66, 95% CI 1.35 to 23.68; 1 trial, n=69 women, evidence graded low; RR 0.29, 95% CI 0.11 to 0.80; 1 trial, n=69), and frequency of leg cramps: 50% reduction in number of leg cramps after treatment (RR 1.42, 95% CI 1.09 to 1.86; 1 trial, n=86, evidence graded low). The outcomes that showed no difference were: frequency of leg cramps during 2 weeks of treatment (mean difference (MD) 1.80, 95% CI -1.32 to 4.92; 1 trial, n=38, evidence graded low); frequency of leg cramps after treatment: daily, every other day, and once a week in one trial with 69 women (RR 1.20, 95% CI 0.45 to 3.21; RR 0.44, 95% CI 0.12 to 1.57; RR 1.54, 95% CI 0.62 to 3.87). Evidence about whether magnesium supplements reduced the intensity of pain was inconclusive.
A greater proportion of women receiving calcium supplements experienced no leg cramps after treatment than those receiving no treatment (frequency of leg cramps after treatment: never RR 8.59, 95% CI 1.19 to 62.07; 1 trial, n=43, evidence graded very low). There was no difference between groups for a composite outcome (intensity and frequency) for partial improvement (RR 0.64, 95% CI 0.36 to 1.15; 1 trial, n=42); however, the same trial showed a greater proportion of women experiencing no leg cramps after treatment with calcium compared with no treatment (RR 5.50, 95% CI 1.38 to 21.86). There was no difference in the frequency of leg cramps after treatment with calcium versus vitamin C (RR 1.33, 95% CI 0.53 to 3.38; 1 trial, n=60, evidence graded very low).
The trials were of moderate quality. The only placebo-controlled trial of calcium treatment showed no evidence of benefit. Trials comparing sodium chloride with placebo (OR 0.54, 95% CI 0.23 to 1.29) and calcium with sodium chloride (OR 1.23, 95% CI 0.47 to 3.27) showed not evidence of benefit. Placebo controlled trials of multivitamin plus mineral supplements (OR 0.23, 95% CI 0.05 to 1.01) and magnesium (OR 0.18, 95% CI 0.05 to 0.60) provides some suggestion of benefit.Comment: The quality of evidence is downgraded by sparse data and study limitations.