Temporal Relationship Between Depression and Dementia Findings From a Large Community-Based 15-Year Follow-up Study

Context: Late-life depression is associated with increased risk of dementia, but the temporal relationship between depression and development of dementia remains unclear. Objectives: To examine the association between risk of dementia and baseline depressive symptoms; history of depression, particularly early-life (<50 years) vs late-life depression (>= 50 years); and individual domains of the Center for Epidemiologic Studies Depression Scale. Design: A large cohort with initially nondemented participants was followed up biennially for up to 15 years. Baseline depressive symptoms were assessed using the 11-item version of the Center for Epidemiologic Studies Depression Scale; presence of significant depressive symptoms was defined as a score of 11 or greater. Self-reported history of depression was collected at the baseline interview. Cox proportional hazards regression was used to assess the association between depression and dementia risk. Setting: Population-based cohort drawn from members of the Group Health Cooperative in Seattle, Washington. Participants: A cohort of 3410 participants without dementia aged at least 65 years. Results: During a mean of 7.1 years of follow-up, 658 participants (19.3%) developed dementia. At baseline, 9.4% of participants had presence of significant depressive symptoms, and 21.2% reported a history of depression. The adjusted hazard ratio for dementia associated with baseline depressive symptoms was 1.71 (95% confidence interval, 1.37-2.13), after adjusting for age at entry, sex, educational level, and wave of enrollment. Compared with participants without depression history, those with late-life depression were at increased dementia risk (adjusted hazard ratio, 1.46; 95% confidence interval, 1.16-1.84), but early-life depression had no association with dementia risk (1.10 [0.83-1.47]). Depressed mood (adjusted hazard ratio, 1.48; 95% confidence interval, 1.25-1.76) and perceived performance difficulty (1.39 [1.15-1.67]) were independently associated with dementia. Conclusion: This study confirmed that late-life depression is associated with increased risk of dementia and supplied evidence that late-life depression may be an early manifestation of dementia rather than increasing risk for dementia.