High iodine dietary intake is associated with type 2 diabetes among women of the E3N-EPIC cohort study

Summary Background Iodine is an essential micronutrient needed for the production of thyroid hormones. Consequently, iodine insufficient and excessive intakes are associated with thyroid disorders. Despite the increase in diabetes prevalence worldwide and the close relationship between thyroid function and the risk of diabetes, the relationship between iodine intake and diabetes has been overlooked. The objective of the present study is to investigate the link between iodine intake and the risk of type 2 diabetes. Methods Cox proportional hazards regression models adjusted on potential confounders were used to calculate the hazard ratios and 95% confidence intervals for the associations between dietary iodine intake and type 2 diabetes risk among 71,264 women of the E3N-EPIC cohort. Results The average iodine intake in the study population was 155.6 μg/day (±47.1 μg/day). After adjusting for the main risk factors for diabetes, for hypo/hyperthyroidism, as well as for phosphorus intakes and consumption of dairy products and seafood, the hazard ratios (95% CI) for type 2 diabetes of women in the 4th (160.7–190.5 μg/day) and 5th (190.6–596.8 μg/day) quintiles groups of iodine intake were 1.27 (1.10–1.47) and 1.28 (1.07–1.53), respectively, compared to women with iodine intake below the 1st quintile (29.3–116.9 μg/day). Conclusion This is the first study to investigate the relationship between dietary iodine intake and the risk of developing type 2 diabetes. More studies are warranted to further investigate the health effects of chronic high iodine intake, and in particular to investigate the biological mechanisms that underlie the association between iodine intake and type 2 diabetes.