The association between magnesium intake and fasting insulin concentration in healthy middle-aged women

OBJECTIVE: We assessed the association between magnesium intake and fasting insulin levels in a large cohort of women. METHODS: Female nurses free of diabetes, cardiovascular diseases and cancer from the Nurses Health Study provided blood samples between 1989-1990. We selected a sub-sample of 219 women for this analysis. Magnesium intake was assessed by a food frequency questionnaire in 1990 and categorized into quartiles. Cross-sectional geometric means of fasting insulin concentrations by quartiles of magnesium intake were obtained with Generalized Linear Model and adjusted for several risk factors and lifestyle characteristics. RESULTS: After adjustment for age, body mass index (BMI), total energy, physical activity, hours per week spent sitting outside work, alcohol intake, smoking, and family history of diabetes, magnesium intake was inversely associated with fasting insulin concentration. The multivariate adjusted geometric mean for women in the lowest quartile of magnesium intake was 11.0 microU/mL and 9.3 microU/mL among those in the highest quartile of magnesium intake (p for trend = 0.04). The inverse association remained when we considered magnesium from only food sources. CONCLUSION: Higher magnesium intake is associated with lower fasting insulin concentrations among women without diabetes. Because lower fasting insulin concentrations generally reflect greater insulin sensitivity, these findings provide a mechanism through which higher dietary magnesium intake may reduce the risk of developing type 2 diabetes mellitus.