Graves' Disease and the Risk of Type 2 Diabetes: A Korean Population-Based Study

Background: Several meta-analyses have found no association between Graves' disease (GD) and an increased risk of incident diabetes; however, the intricate relationship between thyroid dysfunction and diabetes remains underexplored. In this study, we aimed to evaluate the risk of incident type 2 diabetes (T2DM) in a population newly diagnosed with GD, focusing on different treatment methods and treatment duration. Methods: This was a retrospective population-based study utilizing data from the Korean National Health Insurance database. We included 36,243 patients with GD and 36,243 controls, matched with age and sex. We calculated the incidence of T2DM among patients and controls based on treatment methods, such as medical therapy, radioactive iodine therapy (RAIT), and surgery. We examined the cumulative dose and duration of antithyroid drug (ATD) use for each patient. Results: The majority of patients (34,867, 96.2%) were treated with ATDs, followed by RAIT (1093 patients, 3%), and surgery (283 patients, 0.8%). After adjusting for age; sex; income; comorbidities, including hypertension, dyslipidemia, and cancer; body mass index; smoking; drinking; and exercise, patients with GD exhibited a higher risk of developing diabetes (hazard ratio [HR] = 1.13 [95% confidence interval 1.06-1.21]) than controls (5.1% vs. 4.5%, respectively). While the risk was the highest within the first six months after GD diagnosis (HR = 3.21), it was significant between six months and two years (HR = 1.36) and was comparable with the controls two years after GD diagnosis (HR = 0.93). A longer duration of ATD treatment and a higher cumulative dose were associated with an increased risk of diabetes. However, the risks for T2DM did not differ according to treatment modality or clinical outcomes, which was probably related to the small number of patients in each subgroup. Conclusions: Our findings highlight the negative impact of GD on the development of T2DM. Patients newly diagnosed with GD can be considered for diabetes screening to facilitate early detection and intervention.