Effect of magnesium on leg cramps during pregnancy - adapted from the American Journal of Obstetrics

Date: Oct, 1995

A secondary magnesium deficiency may occur in association with pregnancy and lactation. Leg cramps may occur in 5 to 30 percent of all pregnant women. Studies have shown good results with magnesium therapy for the treatment of nocturnal leg cramps in elderly men and women and in patients with type I (insulin-dependent) diabetes mellitus. Dahle and associates evaluated whether oral magnesium supplementation could relieve leg cramps associated with pregnancy.

The randomized, controlled trial included 73 pregnant women with no other complications or medical problems. The study subjects received either 5 mmol of magnesium or placebo. Serum levels of total magnesium and ionized calcium were measured before therapy was started and on completion of treatment. The two groups were statistically well matched for all factors, including description of leg cramp symptoms. The mean duration of symptoms in both groups was 8.1 weeks.

A significant difference was apparent between the groups after three weeks of treatment. Both groups showed a decrease in frequency of symptoms; both groups initially had symptoms an average of once every other day, but this frequency decreased to once every three days in the placebo group and to one or two episodes a week in the magnesium group. Members of the magnesium group also had significantly fewer symptoms on the day after leg cramps occurred during the night.

The incidence of subjectively expressed distress was significantly lower in the magnesium group than in the placebo group. The overall grading of treatment effect in the magnesium group indicated that patients improved "considerably" or became asymptomatic, as compared with the placebo group. Side effects were infrequent in both groups, and compliance did not differ between the groups. No adverse effects of simultaneous oral vitamin and iron supplementation occurred. However, the possibility of positive vitamin synergism with magnesium cannot be answered by this trial.

No laboratory test results changed after treatment, with the exception of total 24hour urinary magnesium excretion in the magnesium group. Total serum magnesium remained at or below the lower reference limit for both groups and was lower than would be expected in women who were not pregnant.

The authors conclude that oral magnesium supplementation in patients with pregnancy-induced leg cramps produces significant relief of symptoms with no adverse side effects. The exact milligram equivalent of the dosage given in this study would be 122 mg of magnesium taken once in the morning and twice in the evening. The synergistic effect of multivitamins and ferrous sulfate warrants further study. (American Journal of Obstetrics and Gynecology, July 1995, vol.173, p.175.)

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