Magnesium for the Treatment of Nocturnal Leg Cramps A Crossover Randomized Trial

Discussion

Magnesium is commonly prescribed for treating nocturnal leg cramps in many Latin American and some European countries. Only one previous randomized double-blind controlled trial²⁰ had been conducted to evaluate magnesium efficacy, and that study was performed on pregnant women. In that study, patients improved with magnesium treatment (a combination of citrate and lactate). We designed our study to evaluate if magnesium was effective in men and nonpregnant women. Our study was a controlled trial with a randomized crossover design similar to the study by Connolly and colleagues.²¹ This design allowed us to control for each patient’s personal confounding bias (every patient is his own control), but leaves the chance for a period effect. Although magnesium was not effective in relieving nocturnal leg cramps, we observed a period-effect bias, as all patients improved over time, regardless of the sequence of treatment they received. This finding was statistically significant. The effect may be explained by a combination of: (1) the natural variability of the symptom, (2) regression to the mean, and (3) a true placebo effect.

Conclusions

We cannot explain why magnesium was effective in pregnant women,¹⁸ but the physiopathology may be different in this subset of women. On the basis of our findings, we do not support the use of magnesium citrate for the treatment of nocturnal leg cramps.

Acknowledgments

Funding was provided by the Fundación MF para el desarrollo de la medicina familiar y la atención primaria de la salud.