Objective: The effect of type of depressive disorder on mortality has been rarely addressed in the relevant literature. It is especially true in considering comorbid disorders and by population-based longitudinal cohort sample. The aims of this study are to compare all-cause and unnatural (suicides and accidents) mortality rates between subjects with bipolar depression (BD) and those with other types of depression (OTD).
Method: A cohort of patients diagnosed as clinically depressed between 1999 and 2004 according to the National Health Insurance Dataset (NHID) were followed until the end of 2008. The occurrence of death was identified by the National Mortality Registry (NMR) in Taiwan. Patients in this cohort were further classified into BD and OTD groups. Proportional hazards regression model were used to evaluate the different mortality risks between two groups.
Results: BD (n = 1542) was associated with a significantly greater risk in all-cause mortality (adjusted hazard ratio = 1.3, 95% CI: 1.1, 1.5) than was OTD (n = 17,480), even after controlling for demographic features and comorbid disorders. BD was associated with approximately twice the risk for suicide and accidental death compared with OTD after other variables were held constant. Bipolar depression (v.s. OTD) exerted adjusted hazard ratio 3.76 (95% CI: 2.17, 6.51) in depressed patients with CVD but only aHR 1.43 (95% CI: 0.79, 2.58) in those without CVD.
Conclusions: Compared with OTD, BD was related to a significantly increased risk for all-cause mortality, suicide, and accidental death. Under the comorbidity with CVD, the risk of suicide was 4-fold times more likely in BD than in OTD. This magnitude of suicide risk among BD patients comorbid with CVD was also higher than those BD without CVD. Thus, patients with both BD and CVD may constitute one of groups at highest risk for suicide and accidental death.
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