Association between depression and diabetes mellitus and the impact of their comorbidity on mortality: Evidence from a nationally representative study

Background: Depression and diabetes mellitus (DM) are major chronic noncommunicable diseases that impair one's mental and physical well-being and impose substantial burdens on the health system. Depressed individuals have an increased risk of impaired blood glucose, weight gain and dyslipidemia which could induce poorer long-term survival. Methods: 37,040 individuals from the National Health and Nutrition Examination Survey (NHANES) were included. Depressive symptoms were assessed by the Patient Health Questionnaire (PHQ-9) and classified by the total scores as no (0-4), mild (5-9), moderate (10-14), and severe (15-27). DM was determined based on selfreported medical history, clinical test results, and medication use. Logistic and Cox regression were the main statistical models. All analyses were based on weighted data from complex sampling. Results: The prevalence of DM was higher in depressed than non-depressed individuals (21.26 % vs. 13.75 %). The adjusted odds ratio (OR) (95 % CI) of comorbid DM increased with depression severity, from 1.00 (reference) for no depression, to 1.22 (1.09,1.36) for mild, 1.62 (1.37,1.92) for moderate, and 1.52(1.28,1.82) for severe depression. Comorbidity of DM and depression significantly associated with a higher risk of all-cause mortality, with a hazard ratio (HR) (95 % CI) = 2.09 (1.64,2.66). Limitations: Dynamic demographic and metabolic data were not available. Conclusion: Depression is associated with a higher risk of DM, which may be related to biological, socioeconomic, and medication-related factors. Comorbidity of the two worsens long-term survival. Therefore, blood glucose management and prevention of DM should be emphasized in depressed patients.