Dietary Magnesium May Help Prevent Development of Type 2 Diabetes

Laurie Barclay, MD

December 23, 2003

Dec. 23, 2003 -- Magnesium-containing foods can prevent development of type 2 diabetes in both men and women, according to the results of a large cohort trial published in the January issue of Diabetes Care. A second cohort study in the same issue showed a similar benefit, especially for overweight women. The editorialist suggests that there is now compelling evidence to support randomized controlled trials.

"Our findings suggest a significant inverse association between magnesium intake and diabetes risk," write Ruy Lopez-Ridaura, MD, and colleagues from Harvard Medical School in Boston, Massachusetts. "This study supports the dietary recommendations to increase consumption of major food sources of magnesium, such as nuts, whole grains, and green leafy vegetables."

The study population consisted of 85,060 women and 42,872 men with no history of diabetes, cardiovascular disease, or cancer at baseline. Using a validated food frequency questionnaire every two to four years, the investigators determined dietary magnesium intake. During follow-up of 18 years in women and 12 years in men, there were 4,085 incident cases of type 2 diabetes in women and 1,333 cases in men.

Comparing the highest with the lowest quintile of total magnesium intake, the relative risk (RR) of type 2 diabetes, after adjustment for age, body mass index (BMI), physical activity, family history of diabetes, alcohol consumption, and history of hypertension and hypercholesterolemia at baseline, was 0.66 (95% confidence interval [CI], 0.60-0.73) in women and 0.67 in men (95% CI, 0.56-0.80; P for trend < .001 in both sexes).

Further adjustments for other dietary variables did not affect the inverse association between magnesium intake and reduced diabetes risk, nor did subgroup analysis according to BMI, physical activity, or family history of diabetes.

Study limitations include inability to screen for blood glucose, resulting in failure to diagnose some cases of diabetes, and possible residual confounding.

"Higher magnesium intake is likely more beneficial among individuals with some degree of magnesium deficiency," the authors write. "This effect of magnesium supplementation in general or high-risk populations requires further research, ideally in randomized clinical trials."

The National Institutes of Health and the National Institutes of Diabetes and Digestive and Kidney Diseases supported this study.

In a separate study of a cohort from the Women's Health Study, higher magnesium intake reduced diabetes risk by about 10% overall, or by about 20% in overweight women.

In an accompanying editorial, Jerry L. Nadler, MD, from the University of Virginia Health Science System in Charlottesville, suggests that there is now compelling evidence to support randomized controlled trials. "If increased magnesium intake is beneficial, it could provide a new, cost-effective way to reduce development of type 2 diabetes," he writes.

Diabetes Care. 2003;27:134-140,59-65,270-271

Reviewed by Gary D. Vogin, MD

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