Higher iron storage has been linked to an increased risk of type 2 diabetes, but little is known about the mediator of this association. Here, we prospectively investigated the association between circulating ferritin, a marker of iron storage, and the incidence of type 2 diabetes among Japanese individuals.Materials and Methods:
The participants were 4,754 employees who attended a comprehensive health check-up in 2008–2009 and donated blood for the study. During 5 years of follow up, diabetes was identified based on plasma glucose, glycated hemoglobin and self-report. Two controls matched to each case on sex, age and date of check-up were randomly chosen using density sampling, giving 327 cases and 641 controls with ferritin measurement. Cox proportional hazards regression was used to estimate the hazard ratio while adjusting for a series of potential confounders or mediators.Results:
Elevated serum ferritin levels were associated with a significantly increased risk of type 2 diabetes, with the hazard ratio adjusted for known risk factors in the highest vs lowest quartile of 1.42 (95% confidence interval: 1.03–1.96). This association was unchanged after adjustment for C-reactive protein and adiponectin, but attenuated after adjustment for liver enzyme and insulin resistance (hazard ratio 1.04). The ferritin–diabetes association was confined to non-obese participants.Conclusions:
These results suggest that elevated iron storage is associated with increased risk of type 2 diabetes in normal weight individuals, and that this association is partly mediated through liver dysfunction and resulting insulin resistance.