Excessive iron stores can cause type 2 diabetes among patients with hemochromatosis, a genetic defect in the regulation of iron absorption, according to background information in the article. However, the authors write that it is not clear if moderately elevated iron stores predict the risk of developing type 2 diabetes among healthy individuals. The authors note that iron excess seems to contribute initially to insulin resistance and subsequently to decreased insulin secretion.
Rui Jiang, M.D., Dr.P.H., from the Harvard School of Public Health, Boston, and colleagues, evaluated biomarkers reflecting iron stores, including plasma ferritin (an iron-protein complex in blood) concentration and the ratio of the concentrations of transferrin receptors (iron transporters) to ferritin in relation to the development of type 2 diabetes in apparently healthy middle-aged women enrolled in the Nurses' Health Study. Of the 32,826 women who provided blood samples during 1989 - 1990 and were free of diagnosed diabetes, cardiovascular disease, and cancer, 698 developed diabetes during 10 years of follow-up. The researchers randomly selected 716 women from the study to be in the control group who were free from diabetes.
"Overall, women who subsequently developed diabetes during follow-up were heavier, more likely to have a family history of diabetes, less likely to exercise and consume alcohol, and had higher plasma concentrations of CRP (C-Reactive Protein - a biomarker for inflammation), fasting insulin, and hemoglobin A1c at baseline," the authors found. "In addition, diabetic women tended to have higher baseline average intake of heme iron [a type of iron], transfat, red and processed meats, total calories, and lower intake of cereal fiber and magnesium. ... At baseline, the mean (average) ferritin concentration was significantly higher (109 vs. 71.5 ng [nanograms]/mL [milliliter]) and the mean ratio of transferrin receptors to ferritin was significantly lower (102 vs. 141) in the cases [those with type 2 diabetes] than in the healthy controls."
In conclusion the authors write, "This finding may have important implications for the prevention of type 2 diabetes because elevated ferritin concentration and lower concentration in the ratio of transferrin receptors to ferritin in healthy populations may help to identify a high-risk population for type 2 diabetes who may benefit from further evaluation and interventions (lifestyle or therapeutic)."
(JAMA. 2004;291:711-717. Available post-embargo at JAMA.com.)
Editor's Note: This work was supported by research grants from the National Institutes of Health. Co-author Dr. Meigs is supported in part by a Career Development Award from the American Diabetes Association.
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