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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.