Magnesium for skeletal muscle cramps

Background Skeletal muscle cramps are common and often presented to physicians in association with pregnancy, advanced age, exercise or disorders of the motor neuron (such as amyotrophic lateral sclerosis). Magnesium supplements are marketed for the prophylaxis of cramps but the efficacy of magnesium for this indication has never been evaluated by systematic review. Objectives To assess the effects of magnesium supplementation compared to no treatment, placebo control or other cramp therapies in people with skeletal muscle cramps. Search methods We searched the Cochrane Neuromuscular Disease Group Specialized Register (11 October 2011), the Cochrane Central Register of Controlled Trials (CENTRAL) (2011, Issue 3), MEDLINE (January 1966 to September 2011), EMBASE (January 1980 to September 2011), LILACS (January 1982 to September 2011), CINAHL Plus (January 1937 to September 2011), AMED (January 1985 to October 2011) and SPORTDiscus (January 1975 to September 2011). Selection criteria Randomized controlled trials (RCTs) of magnesium supplementation (in any form) to prevent skeletal muscle cramps in any patient group (i.e. all clinical presentations of cramp). We considered comparisons of magnesium with no treatment, placebo control, or other therapy. Data collection and analysis Two authors independently selected trials for inclusion and extracted data. Two authors assessed risk of bias. We attempted to contact all study authors and obtained patient level data for three of the included trials, one of which was unpublished. All data on adverse effects were collected from the included RCTs. Main results We identified seven trials (five parallel, two cross‐over) enrolling a total of 406 individuals amongst whom 118 cross‐over participants additionally served as their own controls. Three trials enrolled women with pregnancy‐associated leg cramps (N = 202) and four trials enrolled idiopathic cramp sufferers (N = 322 including cross‐over controls). Magnesium was compared to placebo in six trials and to no treatment in one trial. For idiopathic cramps (largely older adults presumed to have nocturnal leg cramps), differences in measures of cramp frequency, magnesium versus placebo, were small, not statistically significant, and without heterogeneity (I2 = 0%). This includes the primary endpoint, percentage change from baseline in the number of cramps per week at four weeks (‐3.93%, 95% confidence interval (CI) ‐21.12% to 13.26%, moderate quality evidence) and the