We tested the hypothesis that the accumulation of iron in the body predicts the development of non-insulin dependent diabetes. We followed 1038 randomly selected men from eastern Finland aged 42-60 for four years; there is a high incidence of non-insulin dependent diabetes in eastern Finland. Fifty three men who were found to have diabetes at baseline (fasting blood glucose concentration
mmol/l or who were already receiving treatment for diabetes) were excluded. This low cut off point for fasting blood glucose was used to increase the sensitivity of the exclusion of participants so that all potential participants who had diabetes or who could have been classed as prediabetic were excluded.
We estimated iron stores by determining the ratio of the concentrations of transferrin receptors5
to ferritin in frozen serum samples drawn during baseline examinations. Serum samples from 41 men who developed diabetes during follow up and from 82 controls were analysed. The controls were matched by age, year and month of examination, place of residence (urban or rural), number of cigarettes smoked daily, amount of exercise taken each week (kcal expended per week), maximal oxygen uptake (a measure of cardiorespiratory fitness), socioeconomic status, height, weight, hip and waist circumferences, blood glucose concentration, serum insulin concentration, plasma lipid standardised vitamin E concentration, and the ratio of saturated fatty acids to the sum of polyunsaturated and monounsaturated fatty acids in serum at baseline.4
A participant was defined as diabetic at the end of follow up if he had a fasting blood glucose concentration
mmol/l (a higher cut off value was used to increase specificity), or a blood glucose concentration two hours after glucose loading
10.0 mmol/l, or a clinical diagnosis of diabetes and was receiving dietary, oral, or insulin treatment.4
In a logistic regression model, men with high stores of iron (those in the lowest quarter of the ratio of transferrin receptors to ferritin, that is <9.4
μg/μg) were 2.4 times more likely (95% confidence interval of odds ratio 1.03 to 5.5, P=0.04) to develop diabetes than men with lower stores of iron. In a step up model in which baseline concentrations of serum triglycerides and glycosylated proteins were adjusted for as continuous variables, the odds ratio for developing diabetes was 2.5 (1.1 to 6.0, P=0.04).