Synergistic effects of depression and obesity on type 2 diabetes incidence in Chinese adults.

Background Cross-sectional studies have supported the association among depression, obesity, and type 2 diabetes, but the causality remains controversial in Chinese adults. In this longitudinal study, we evaluated the synergistic effect of depression and obesity on the risk of type 2 diabetes. Methods This study included 2809 participants randomly selected from the Qingdao Diabetes Prevention Program, and their type 2 diabetes incidence was determined over a follow-up period of 3 years. The WHO 2006 criteria and the Zung Self-Rating Depression Scale score were employed to identify type 2 diabetes and depression at baseline, respectively. Multivariable-adjusted logistic regression was used to evaluate the synergistic effects of depression and obesity indicators on type 2 diabetes, with adjustment for age, sex, family history of diabetes, and other potential risk factors. Results During 3-year follow-up, 316 new incident cases were identified. The relative risk and 95% confidence interval of depression for diabetes incidence was 1.52 (1.05-2.21), after controlling for potential confounders. Sensitivity analysis showed that depression was significantly associated with diabetes incidence in women, younger people, and obese people (1.82 [1.14-2.92], 1.94 [1.25-3.02], and 4.29 [1.44-12.78], respectively]. The synergistic effects of positive depression and body mass index >= 30 kg/m(2) on type 2 diabetes incidence were observed, with a synergy index of 5.49 (1.75-17.19). Conclusions Depression was associated with a 52% increased risk of type 2 diabetes incidence and exerts synergistic effects with obesity on diabetes incidence in Chinese adults. Early identification and intervention for depression and obesity can reduce the risk of diabetes.