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J Gerontol A Biol Sci Med Sci. 2011 Jun;66(6):661-6. doi: 10.1093/gerona/glq232. Epub 2011 Feb 2.

The effect of magnesium infusion on rest cramps: randomized controlled trial.

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Centre for Hip Health and Mobility, University of British Columbia, 303-2647 Willow Street, Vancouver, Canada V5Z 3P1.



Rest cramps (also known as nocturnal leg cramps) are very common in a geriatric population. Oral magnesium supplements are marketed for prophylaxis of such cramps but clinical trials exploring the efficacy of oral magnesium conflict. A therapeutic trial of intravenous magnesium overcomes the limited oral bioavailability of magnesium and better assesses its therapeutic potential.


A double blind, placebo controlled randomized controlled trial was conducted on 46 community-dwelling older adult (69.3 ± 7.7 years) rest cramp sufferers to determine whether 5 consecutive days infusion of 20-mmol (5 g) magnesium sulfate would reduce the frequency of leg cramps per week in the 30 days immediately pre and post infusions. It was also determined whether the response to treatment varied with the extent to which infused magnesium was retained (as measured by 24-hour urinary magnesium excretion).


The study population averaged 8.0 cramps per week at baseline. The mean change in number of cramps per week, magnesium versus placebo arms, was -2.4 versus -1.7, p = .51, 95% confidence interval of the difference -3.1 to 1.7. Magnesium retention did not correlate with treatment response.


Intravenous magnesium infusion did not reduce the frequency of leg cramps in a group of older adult rest cramp sufferers regardless of the extent to which infused magnesium was retained. Although oral magnesium is widely marketed to older adults for the prophylaxis of leg cramps, our data suggest that magnesium therapy is not indicated for the treatment of rest cramps in a geriatric population.

[Indexed for MEDLINE]

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