Dietary iron intake and blood donations in relation to risk of type 2 diabetes in men: a prospective cohort study

BACKGROUND: Excessive iron stores may promote insulin resistance and lead to the development of type 2 diabetes. However, prospective data relating iron intake and blood donations (determinants of body iron stores) to diabetes incidence are limited. OBJECTIVE: We examined iron intake and blood donations in relation to the incidence of type 2 diabetes. DESIGN: We followed men aged 40-75 y who participated in the Health Professionals' Follow-up Study; were free of diabetes, cardiovascular disease, and cancer in 1986; and provided dietary data (n = 38 394). Of those participants, 33 541 also provided a history of blood donation during the past 30 y in 1992. RESULTS: During 12 y of follow-up, we ascertained 1168 new cases of type 2 diabetes. After adjustment for age, body mass index, and other diabetes risk factors, total iron intake was not associated with the risk of type 2 diabetes. Intakes of total heme iron [multivariate relative risk (RR) for extreme quintiles: 1.28; 95% CI: 1.02, 1.61; P for trend = 0.045] and of heme iron from red meat (RR: 1.63; 1.26, 2.10; P for trend < 0.001) were associated with an increased risk. However, heme-iron intake from sources other than red meat was not associated with diabetes risk (RR: 0.99; 0.81, 1.22). No significant associations were found between blood donation and the risk of type 2 diabetes. CONCLUSIONS: Heme-iron intake from red meat sources is positively associated with the risk of type 2 diabetes. Total iron intake, heme-iron intake from non-red meat sources, and blood donations are not related to the risk of type 2 diabetes.