Higher Body Iron Stores Predict Future Risk of Women Developing Type 2 Diabetes

Source: Harvard School of Public Health,  February 10, 2004

Study Identifies A Novel Biomarker For Type 2 Diabetes

Boston, MA – In the first large study to assess iron stores and risk of type 2 diabetes in an apparently healthy population, researchers from the Harvard School of Public Health (HSPH) found that higher iron stores were associated with significantly elevated risk of type 2 diabetes, independent of other known diabetes risk factors.  Higher iron stores were assessed by measuring blood concentrations of ferritin (a protein that stores iron in the body). The findings appear in the February 11, 2004 issue of the Journal of the American Medical Association (JAMA).

More than 32,800 women participants were selected from the on-going Brigham and Women’s Hospital-based Nurses’ Health Study, who had provided blood samples between 1989 and 1990 and were free of diabetes, cardiovascular disease and cancer. Over a ten year span of follow-up, participants provided information on diet and lifestyle via questionnaires. Some 698 women were diagnosed with type 2 diabetes during the course of the study with a total of 716 healthy women selected as controls.

Compared with the healthy controls, women who developed type 2 diabetes during the course of the study had significantly elevated ferritin levels when blood samples were initially drawn.  Compared with women with the lowest ferritin concentration, those with higher ferritin levels had a nearly 3-fold increased risk of developing type 2 diabetes during the 10 years of follow-up.  The researchers measured another biomarker, transferrin receptors in the blood (transferrin acts as a carrier for iron in the bloodstream). Lower transferrin receptors/ferritin ratio also reflects increased iron storage in the body.  Those with the lowest transferrin receptors/ferritin ratio had a relative risk more than 2.5 times higher for onset of type 2 diabetes compared to those in the study with the highest ratio. Adjusting for obesity and other diabetes risk factors including family history of diabetes, physical activity, smoking status, alcohol consumption and diet, did not change the results.

The researchers noted that although previous small studies documented a relationship between body iron stores and diabetes risk, this is the first large prospective study relating iron stores and future risk of developing type 2 diabetes in a healthy population.  Adequate iron is important for health because it is essential for oxygen transport and cell functions.  Excess levels of iron, however, can increase cellular oxidative stress and damage tissues because it is a potent pro-oxidant.  This may lead to insulin resistance and abnormal glucose metabolism, elevating risk of type 2 diabetes.

“The results provide the strongest evidence to date that increased iron stores in the body are an independent risk factor for type 2 diabetes,” said Rui Jiang, lead author and a research fellow in the Department of Nutrition at HSPH.  Frank Hu, senior author of the study and an associate professor of Nutrition and Epidemiology at HSPH added, “The findings suggest that a simple blood test which measures ferritin levels can be used to predict the development of type 2 diabetes in otherwise healthy people. This may help in identifying high-risk people who would possibly benefit from further lifestyle or therapeutic interventions that can lower iron stores in the body.”

The research was supported by grants from the National Institutes of Health and from the American Diabetes Association.

*The fact that excess dietary iron may be dangerous for men or post-menopausal women does not mean the same is true for children, adolescents and women of child-bearing age as they often do not get enough iron.