Dietary iron intake and Type 2 diabetes incidence in postmenopausal women: the Iowa Women's Health Study.

AIMS/HYPOTHESIS: Recently, a clear biological link between iron metabolism and diabetes has emerged from epidemiological and experimental studies. We carried out a prospective study of dietary iron intake and incidence of Type 2 diabetes.
METHODS: 35,698 postmenopausal women initially aged 55 to 69 years were followed for 11 years. Diet was assessed with a food frequency questionnaire at baseline.
RESULTS: Intake of heme iron showed a positive association with incident Type 2 diabetes; the relative risks were 1.0, 1.07, 1.12, 1.14, and 1.28 across quintiles of heme iron (p trend =0.02) after adjustment for non-dietary and dietary risk factors. Heme iron showed a weak positive association among non-drinkers, but the association appeared to be stronger among subjects who consumed more alcohol. For example, in a model restricted to those who drank alcohol at least 15 g/day, adjusted relative risks across quintiles of heme iron were 1.0, 2.26, 3.22, 1.92, and 4.42 (p trend =0.05); and consumers of 30 g/day of more of supplemental iron had an adjusted relative risk equal to 3.03 (95% CI, 1.29-7.12)], compared to those who took no iron supplement. Non-heme iron was inversely associated with incidence of Type 2 diabetes. Amongst non-drinkers adjusted relative risks were 1.0, 0.83, 0.87, 0.72, and 0.67 across quintiles (p trend <0.01). This inverse association was lost among drinkers, in whom there was no association of diabetes incidence with non-heme iron. CONCLUSIONS/
INTERPRETATION: Greater dietary heme-iron intake and/or supplemental iron were associated with an increased risk of Type 2 diabetes, especially amongst those who drink alcohol.