BOSTON, MASSACHUSETTS. The incidence of type 2 diabetes is growing rapidly throughout the world and diabetes is now a major global health problem. Researchers at the Harvard School of Public Health believe that a magnesium deficiency could well be part of the problem. Their study involved 85,060 female nurses and 42,872 male health professionals who were free of diabetes, cancer and cardiovascular disease at baseline. The participants completed food frequency questionnaires every 2 years throughout the study. After 18 years of follow-up 4,085 of the nurses had developed type 2 diabetes corresponding to an annual incidence of 0.3%. Among the men 1,333 cases were reported after 12 years of follow-up, also corresponding to an annual incidence of 0.3%.
After adjusting for age, family history of diabetes, smoking, alcohol consumption, body mass index (BMI), physical activity, high cholesterol levels, and a history of hypertension the researchers concluded that diabetes is associated with a low intake of magnesium. Women (female nurses) with an average daily intake of 377 mg of elemental magnesium had a 34% lower risk of developing diabetes than did those with an average daily intake of only 217 mg. Among the men (male health professionals) those with an average intake of 458 mg/day had a 33% lower risk of developing diabetes than did those with an average daily intake of 268 mg. Daily magnesium intake was positively associated with intakes of fiber and inversely associated with intake of processed meat and fat. Only 3.1% of women and 3.6% of men used magnesium supplements, so it is not possible to say from this study whether supplements would be beneficial. There was no association between the use of multivitamins and diabetes risk.
The average magnesium intake among all women was 290 mg/day and that among men was 349 mg/day.
The RDA for a 70 kg man is 420 mg/day. At least 84% of the male study participants had an intake below
420 mg/day. The RDA for a 57 kg woman is 340 mg/day. At least 84% of the female participants had an
intake below 340 mg/day. In other words, at least 84% of all the study participants were likely deficient in
magnesium intake. The researchers suggest clinical trials to evaluate the effect of magnesium
supplementation on diabetes risk.
Editor's comment: Whole grains, nuts and green leafy vegetables are good sources of magnesium. However, the study clearly shows that the average American diet is seriously deficient in magnesium. The most common magnesium supplement, magnesium oxide, is very poorly absorbed; so widespread supplementation with this product is unlikely to show much benefit. The most absorbable supplements are magnesium glycinate (chelated magnesium), magnesium taurate, and magnesium citrate.