Severity of depressive symptoms as a predictor of mortality: the English longitudinal study of ageing

BACKGROUND: Major depressive disorder and subthreshold depression have been associated with premature mortality. We investigated the association between depressive symptoms and mortality across the full continuum of severity. METHOD: We used Cox proportional hazards models to examine the association between depressive symptom severity, assessed using the eight-item Center for Epidemiological Studies Depression Scale (CES-D; range 0-8), and the risk of all-cause mortality over a 9-year follow-up, in 11 104 members of the English Longitudinal Study of Ageing. RESULTS: During follow-up, one fifth of study members died (N = 2267). Depressive symptoms were associated with increased mortality across the full range of severity (p trend < 0.001). Relative to study members with no symptoms, an increased risk of mortality was found in people with depressive symptoms of a low hazard ratio (HR) for a score of 2 was 1.59, 95% confidence interval (CI) 1.40-1.82, moderate (score of 4: HR 1.80, 95% CI 1.52-2.13) and high (score of 8: HR 2.27, 95% CI 1.69-3.04) severity, suggesting risk emerges at low levels but plateaus thereafter. A third of participants (36.4%, 95% CI 35.5-37.3) reported depressive symptoms associated with an increased mortality risk. Adjustment for physical activity, physical illnesses, and impairments in physical and cognitive functioning attenuated this association (p trend = 0.25). CONCLUSIONS: Depressive symptoms are associated with an increased mortality risk even at low levels of symptom severity. This association is explained by physical activity, physical illnesses, and impairments in physical and cognitive functioning.