Magnesium intake, quality of carbohydrates, and risk of type 2 diabetes: results from three U.S. cohorts

Authors: HRUBY, ADELA - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; GUASCH-FERRE, MARTA - Harvard University; BHUPATHIRAJU, SHILPA - Harvard University; MANSON, JOANN - Harvard University; WILLETT, WALTER - Harvard University; MCKEOWN, NICOLA - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; HU, FRANK - Harvard University

Submitted to: Diabetes Care
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2017
Publication Date: 10/4/2017
Citation: Hurby, A., Guasch-Ferre, M., Bhupathiraju, S.N., Manson, J.E., Willett, W.C., McKeown, N.M., Hu, F.B. 2017. Magnesium intake, quality of carbohydrates, and risk of type 2 diabetes: results from three U.S. cohorts. Diabetes Care. https://doi.org/10.2337/dc17-1143.
DOI: https://doi.org/10.2337/dc17-1143

Interpretive Summary: Dietary intake of magnesium, a mineral found in many foods that is critical for human health, is thought to be associated with lower risk of developing diabetes. High quality carbohydrate-rich foods, such as whole grains, have also been linked to lower risk of developing diabetes, as compared to low-quality carbohydrate foods, such as sugar-sweetened beverages, like cola. A good source of magnesium happens to be grain-based foods, particularly whole-grain foods, because the mineral is present in the components of the grain which are retained in the final food product. Researchers wanted to know whether magnesium is beneficial for lowering risk of diabetes even in the presence of a diet with high-quality carbohydrates, or whether it can be helpful for people who don't include a lot of high-quality carbohydrates in their diets. Researchers attempted to answer this question by investigating the relationship between magnesium intake, carbohydrate quality of the diet, and the risk of developing diabetes in 3 large studies involving over 200,000 people without diabetes, and followed them for up to 28 years. Just over 17,000 of these individuals developed diabetes in that time period. Researchers found that consistent with earlier data, people with the highest magnesium intake had 15% lower risk of type 2 diabetes compared with those with the lowest intake and that higher magnesium intake was more strongly associated with lower risk of diabetes in participants with lower quality diets (low carbohydrate quality and/or low fiber intake) than among those with higher quality diets. The researchers concluded that higher magnesium intake may be particularly beneficial for people who have low fiber intake or intake of predominantly low-quality carbohydrates like sugar-sweetened beverages and/or refined grains.

Technical Abstract: OBJECTIVE: Magnesium intake is inversely associated with risk of type 2 diabetes in many observational studies, but few have assessed this association in the context of the carbohydrate quality of the diet. We hypothesized that higher magnesium intake is associated with lower risk of type 2 diabetes, especially in the context of a poor-carbohydrate-quality diet characterized by low cereal fiber or high glycemic index (GI) or glycemic load (GL). RESEARCH DESIGN AND METHODS: In the Nurses' Health Study (NHS; 1984-2012, n = 69,176), NHS2 (1991-2013, n = 91,471), and the Health Professionals' Follow-Up Study (1986-2012, n = 42,096), dietary intake was assessed from food frequency questionnaires every 4 years. Type 2 diabetes was ascertained by biennial and supplementary questionnaires. We calculated multivariate hazard ratios (HRs) of magnesium intake and incident diabetes, adjusted for age, BMI, family history of diabetes, physical activity, smoking, hypertension, hypercholesterolemia, GL, energy intake, alcohol, cereal fiber, polyunsaturated fats, trans fatty acids, and processed meat, and we considered the joint associations of magnesium and carbohydrate quality on diabetes risk. RESULTS: We documented 17,130 incident cases of type 2 diabetes over 28 years of follow-up. In pooled analyses across the three cohorts, those with the highest magnesium intake had 15% lower risk of type 2 diabetes compared with those with the lowest intake (pooled multivariate HR in quintile 5 vs. 1: 0.85 [95% CI 0.80-0.91], P < 0.0001). Higher magnesium intake was more strongly associated with lower risk of type 2 diabetes among participants with high GI or low cereal fiber than among those with low GI or high cereal fiber (both P interaction <0.001). CONCLUSIONS: Higher magnesium intake is associated with lower risk of type 2 diabetes, especially in the context of lower-carbohydrate-quality diets.