Mortality rates in major and subthreshold depression: 10-year follow-up of a Singaporean population cohort of older adults

OBJECTIVES: To investigate the associations of major and subthreshold depression with all-cause, cardiovascular disease and stroke mortality, and the extent to which health behaviour, medical comorbidity and functional disability explained the associations. METHODS: A cohort of 1070 persons aged ≥60 with Geriatric Mental State (GMS) diagnoses of major and subthreshold depression, and data on health behaviour (smoking, alcohol, physical activity) and physical comorbidity (hypertension, diabetes, cardiovascular disease, stroke, chronic pulmonary disease, multi-comorbidity and activity of daily living disability) at baseline (15 Feb 2003 - 30 Mar 2004) were followed up on mortality from 1 Jan 2005 to 31 Dec 2012. RESULTS: Major and subthreshold depression was present in 5.1% and 9.9% of the participants at baseline. The all-cause mortality HR adjusted for age, sex, ethnicity and marital status was 1.73 (95% CI, 1.11-2.67) for major depression and 1.38 (95% CI, 0.96-1.97) for subthreshold depression. In hierarchical models, the addition of health behaviour and especially physical comorbidity substantially reduced the HR estimates for all-cause mortality associated with major depression (HR=1.39, 95% CI, 0.89-2.18) and subthreshold depression (HR=0.94, 95% CI, 0.64-1.37). Controlling for the effects of all variables, only major depression was significantly associated with increased cardiovascular disease and stroke mortality (HR=2.10, 95% CI, 1.07-4.11). CONCLUSIONS: Both major and subthreshold depression were associated with increased mortality, largely due to hazardous behaviours and physical comorbidity. Only major depression per se was independently associated with excess cardiovascular disease and stroke mortality.