Type 2 Diabetes and Its Association With Psychiatric Disorders in Young Adults in South Korea.

Importance: Because type 2 diabetes (T2D) has become increasingly prevalent among young adults, the study of the association of T2D with psychiatric disorders in young adults is important for early detection and timely intervention. Objective: To determine whether a diagnosis of a psychiatric disorder is associated with increased risk of developing T2D in young adults. Design, Setting, and Participants: This large-scale prospective cohort study used data collected by the South Korean National Health Insurance Service between 2009 and 2012, representing 97% of the South Korean population. Young adults aged 20 to 39 years with and without diagnoses of psychiatric disorders were included in the study. Young adults with missing data and those with a history of T2D were excluded from the study. The cohort was followed up to monitor development of T2D until December 2018. Data were analyzed from March 2021 to February 2022. Exposure: Diagnosis of 1 of 5 psychiatric disorders, including schizophrenia, bipolar disorder, depressive disorder, anxiety disorder, and sleep disorder. Main Outcomes and Measures: The primary outcome was newly diagnosed T2D during a follow-up period of 7.59 years. The incidence rate of T2D was calculated as the number of new cases per 1000 person-years during the follow-up period. The Cox proportional hazards regression model was used to estimate the hazard ratios (HRs) and 95% CIs for T2D incidence. Exploratory analyses were performed for subgroups stratified by age and sex. Results: In total, 6 457 991 young adults (mean [SD] age, 30.74 [4.98] years; 3 821 858 men [59.18%]) were followed up, including 658 430 individuals with psychiatric disorders. The cumulative incidence of T2D differed significantly between individuals with and without psychiatric disorders (log-rank test, P < .001). Incidence rates of T2D for individuals with and without psychiatric disorders were 2.89 and 2.56 per 1000 person-years, respectively. Individuals with a diagnosis of any psychiatric disorder showed a higher risk of developing T2D than those without a diagnosis (adjusted HR, 1.20; 95% CI, 1.17-1.22). The adjusted HRs for T2D were 2.04 (95% CI, 1.83-2.28) for individuals with schizophrenia, 1.91 (95% CI, 1.73-2.12) for individuals with bipolar disorder, 1.24 (95% CI, 1.20-1.28) for individuals with depressive disorder, 1.13 (95% CI, 1.11-1.16) for individuals with anxiety disorder, and 1.31 (95% CI, 1.27-1.35) for individuals with sleep disorder. Conclusions and Relevance: In this large-scale prospective cohort study of young adults, 5 psychiatric disorders were significantly associated with an increased risk of developing T2D. Young adults with schizophrenia and bipolar disorder in particular were at a higher risk of T2D. These results have important implications for early detection of and timely intervention in T2D for young adults with psychiatric disorders.