Disability-free survival by symptoms of depression in older adults: a historical cohort study from the Tsurugaya Project

BACKGROUND: Depressive symptoms have been associated with shorter disability-free survival in older adults; however, whether this association differs according to the structure of depressive symptoms remains unclear. We examined the association between the structure of depressive symptoms and risk of disability or death among older men and women in Japan. METHODS: We analyzed 585 individuals who underwent a comprehensive geriatric assessment and agreed to provide information on long-term care insurance. Factor analysis was performed using items from the Geriatric Depression Scale (GDS-15) to extract factors of depressive symptoms. The endpoint was the composite outcome of disability or death, defined as the first certification of any level of care requirement. Associations between the extracted depressive symptom factors and outcomes were examined using a Cox proportional hazards models. RESULTS: During 18 years of follow-up, 497 incident cases of disability or death occurred. In men, "worthlessness" was positively associated with the incidence of disability or death (hazard ratio [95% confidence intervals], 1.85 [0.98-3.49], P for trend = 0.04) after adjusting for potential covariates. In women, "anxiety" was positively associated with the incidence of disability or death (1.88 [1.15-3.07], P for trend = 0.02), whereas "unhappiness" showed an inverse association with the incidence of disability or death (0.51 [0.30-0.87], P for trend = 0.01). CONCLUSIONS: The association between depressive symptoms and the risk of disability or death in older adults varied according to the structure of depressive symptoms and sex.