Dietary Magnesium Intake in Relation to Plasma Insulin Levels and Risk of Type 2 Diabetes in Women

  1. Yiqing Song, MD12,
  2. JoAnn E. Manson, MD, DRPH123,
  3. Julie E. Buring, SCD124 and
  4. Simin Liu, MD, SCD123
  1. 1Division of Preventive Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts
  2. 2Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts
  3. 3Channing Laboratory, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts
  4. 4Department of Ambulatory Care and Prevention, Harvard Medical School, Boston, Massachusetts
  1. Address correspondence and reprint requests to Simin Liu, MD, ScD, Division of Preventive Medicine, Brigham and Women’s Hospital, 900 Commonwealth Ave. East, Boston, MA 02215. E-mail: simin.liu{at}channing.harvard.edu

Abstract

OBJECTIVE—Higher intake of magnesium appears to improve glucose and insulin homeostasis; however, there are sparse prospective data on the association between magnesium intake and incidence of type 2 diabetes.

RESEARCH DESIGN AND METHODS—In the Women’s Health Study, a cohort of 39,345 U.S. women aged ≥45 years with no previous history of cardiovascular disease, cancer, or type 2 diabetes completed validated semiquantitative food frequency questionnaires in 1993 and were followed for an average of 6 years. We used Cox proportional hazard models to estimate multivariate relative risks (RRs) of type 2 diabetes across quintiles of magnesium intake compared with the lowest quintile. In a sample of 349 apparently healthy women from this study, we measured plasma fasting insulin levels to examine their relation to magnesium intake.

RESULTS—During 222,523 person-years of follow-up, we documented 918 confirmed incident cases of type 2 diabetes. There was a significant inverse association between magnesium intake and risk of type 2 diabetes, independent of age and BMI (P = 0.007 for trend). After further adjustment for physical activity, alcohol intake, smoking, family history of diabetes, and total calorie intake, the multivariate-adjusted RRs of diabetes from the lowest to highest quintiles of magnesium intake were attenuated at 1.0, 1.06, 0.81, 0.86, and 0.89 (P = 0.05 for trend). Among women with BMI ≥25 kg/m2, the inverse trend was significant; multivariate-adjusted RRs were 1.0, 0.96, 0.76, 0.84, and 0.78 (P = 0.02 for trend). Multivariate-adjusted geometric mean insulin levels for overweight women in the lowest quartile of magnesium intake was 53.5 compared with 41.5 pmol/l among those at the highest quartile (P = 0.03 for trend).

CONCLUSIONS—These findings support a protective role of higher intake of magnesium in reducing the risk of developing type 2 diabetes, especially in overweight women.

Footnotes

  • A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances.

    See accompanying editorial, p. 270.

    • Accepted August 22, 2003.
    • Received July 21, 2003.
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