Magnesium for skeletal muscle cramps.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of randomized controlled trials
PubMed 32956536 · doi:10.1002/14651858.CD009402.pub3
What was done
This updated Cochrane systematic review evaluated randomized controlled trials (RCTs) investigating magnesium supplementation in any form compared to placebo, no treatment, or active controls for skeletal muscle cramps. Authors searched multiple databases through September 2019. The review included 11 RCTs (9 parallel-group, 2 cross-over) with 735 total participants across three clinical contexts: idiopathic cramps (5 trials, n=271, mean age 61.6–69.3 years), pregnancy-associated leg cramps (5 trials, n=408), and liver cirrhosis (1 trial, n=29).
What was found
For idiopathic cramps, magnesium showed no statistically significant benefit over placebo across all primary and secondary endpoints at four weeks: - Percentage change from baseline in cramps/week: mean difference (MD) -9.59% (95% CI -23.14% to 3.97%; 3 studies, n=177; moderate-certainty). - Absolute difference in cramps/week: MD -0.18 cramps/week (95% CI -0.84 to 0.49; 5 studies, n=307; moderate-certainty). - Achieving >=25% reduction in cramp frequency: RR 1.04 (95% CI 0.84 to 1.29; 3 studies, n=177; high-certainty). - Cramps rated moderate or severe: RR 1.33 (95% CI 0.81 to 2.21; 2 studies, n=91; moderate-certainty). - Cramp duration >=1 minute: RR 1.83 (95% CI 0.74 to 4.53; 1 study, n=46; low-certainty). For pregnancy-associated cramps, meta-analysis was not possible; individual trial results were conflicting and all five trials were at high risk of bias. Adverse events were primarily minor gastrointestinal issues (e.g., diarrhea), occurring in 11% to 37% of magnesium recipients compared to 10% to 14% of controls (RR 1.51, 95% CI 0.98 to 2.33; 4 studies, n=254).
Why it matters
Despite widespread commercial marketing and clinical use for nocturnal leg cramps, magnesium supplements provide no clinically meaningful cramp prophylaxis for older adults with idiopathic cramps.
Limits
All pregnancy-related trials and the single cirrhosis trial had a high risk of bias and inconsistent outcome reporting. No RCTs were identified that evaluated magnesium for exercise-associated cramps or disease-associated cramps (such as amyotrophic lateral sclerosis). Follow-up across trials was relatively short (typically four weeks).
Cited by
- supports Evidence supporting magnesium supplementation for reducing muscle cramps is generally weak, though some studies suggest benefits in pregnant women.
- supports There is no scientific evidence demonstrating that soaking in Epsom salt increases plasma magnesium levels or improves muscle cramps.