Mortality in unipolar depression preceding and following chronic somatic diseases

OBJECTIVE: It is largely unknown how depression prior to and following somatic diseases affects mortality. Thus, we examined how the temporal order of depression and somatic diseases affects mortality risk. METHOD: Data were from a Danish population-based cohort from 1995 to 2013, which included all residents in Denmark during the study period (N = 4 984 912). Nineteen severe chronic somatic disorders from the Charlson Comorbidity Index were assessed. The date of first diagnosis of depression and somatic diseases was identified. Multivariable Cox proportional Hazard models with time-varying covariates were constructed to assess the risk for all-cause and non-suicide deaths for individual somatic diseases. RESULTS: For all somatic diseases, prior and/or subsequent depression conferred a significantly higher mortality risk. Prior depression was significantly associated with a higher mortality risk when compared to subsequent depression for 13 of the 19 somatic diseases assessed, with the largest difference observed for moderate/severe liver disease (HR = 2.08; 95% CI = 1.79-2.44), followed by metastatic solid tumor (HR = 1.48; 95% CI = 1.39-1.58), and myocardial infarction (HR = 1.40; 95% CI = 1.34-1.49). CONCLUSION: A particularly high mortality risk was observed in the presence of prior depression for most somatic diseases. Future studies that assess the underlying mechanisms are necessary to adequately address the excessive mortality associated with comorbid depression.