OBJECTIVE -Epidemiological studies suggest that high body iron stores are associated with insulin resistance and type 2 diabetes. The aim of this study was to evaluate the association between dietary intake of iron and the risk of type 2 diabetes.RESEARCH DESIGN AND METHODS -We conducted a prospective cohort study within the Nurses' Health Study. We followed 85,031 healthy women aged 34 -59 years from 1980 to 2000. Dietary data were collected every 4 years, and data on medical history and lifestyle factors were updated biennially.RESULTS -During the 20 years of follow-up, we documented 4,599 incident cases of type 2 diabetes. We found no association between total, dietary, supplemental, or nonheme iron and the risk of type 2 diabetes. However, heme iron intake (derived from animal products) was positively associated with risk; relative risks (RRs) across increasing quintiles of cumulative intake were 1.00, 1.08 (95% CI 0.97-1.19), 1.20 (1.09 -1.33), 1.27 (1.14 -1.41), and 1.28 (1.14 -1.45) (P trend Ͻ 0.0001) after controlling for age, BMI, and other nondietary and dietary risk factors. In addition, when we modeled heme iron in seven categories, the multivariate RR comparing women who consumed Ն2.25 mg/day and those with intake Ͻ0.75 mg/day was 1.52 (1.22-1.88). The association between heme iron and the risk of diabetes was significant in both overweight and lean women.CONCLUSIONS -This large cohort study suggests that higher heme iron intake is associated with a significantly increased risk of type 2 diabetes.
Diabetes Care 29:1370 -1376, 2006D iet and lifestyle play a major role in the prevention of type 2 diabetes. The quality and quantity of macronutrients (especially fat and carbohydrates) are known to have an impact on the risk of type 2 diabetes; however, the role of micronutrients is not well established (1). Several studies have suggested a possible role of minerals such as magnesium (2,3), chromium (4,5), calcium (6), and iron (7) in insulin resistance or diabetes.Iron is a transitional metal and a potential catalyst in many cellular reactions that produce reactive oxygen species. Such reactions contribute to tissue damage and increase oxidative stress, thereby potentially altering the risk of type 2 diabetes (8). Several studies have suggested a possible link between high body iron stores and metabolic parameters (9 -13) (serum insulin and glucose) as well as hyp e r t e n s i o n ( 9 , 1 4 ) , d y s l i p i d e m i a (9,15,16), and obesity (9,17). In addition, epidemiological studies have reported an association between high iron stores and increased risk of cardiovascular disease (18), metabolic syndrome (10,12,19), gestational diabetes (20,21), and type 2 diabetes (22-27). The major source of body iron is derived from the diet. Dietary iron exists as either heme (derived from meat and meat products) or nonheme iron. In two recent prospective cohort studies (28,29), intake of total or nonheme iron was not associated with the risk of type 2 diabetes, but heme iron was associated with elevated risk. Th...