Ganguli M, Du Y, Dodge HH, Ratcliff GG, Chang CH. Depressive symptoms and cognitive decline in late life: a prospective epidemiologic study. Archives of General Psychiatry, 63, 153-160, 2006.

ABSTRACT:

Context.   Depression is associated with both cognitive impairment and dementia.  It is less clear whether depression contributes to further cognitive decline over time, independently of incipient dementia.

Objective:  To examine the relationship between depressive symptoms and subsequent cognitive decline in  a cohort of non-demented older adults, some of whom remained dementia-free during follow-up, and others who eventually developed incident  dementia.

Design: 12-year prospective epidemiological study.   Biennial measurement of cognition, depressive symptoms, and assessment of dementia.  Comparison of cognitive function at baseline and over time, in persons with and without baseline depressive symptoms in the dementia-free and eventual-dementia groups, using random effects models.

Setting.  A largely blue-collar rural community.

Participants.  Population-based sample of 1265  adults aged 67+ and without dementia at baseline.

Main Outcome Measure: Scores over time on each of several cognitive test composites.

Results: Among 1094 participants who remained dementia-free, those with baseline depressive symptoms had significantly lower baseline scores on all cognitive composites  than the non-depressed.  Among the 171 individuals who later developed dementia, depression was associated with worse performance in some but not all baseline cognitive composites.  Cognitive decline over time was minimal in the dementia-free group, while marked decline was seen in those with eventual dementia.  Depressive symptoms were not associated with rate of cognitive decline over time in either group.

Conclusions: Depressive symptoms are cross-sectionally associated with cognitive impairment but not with subsequent cognitive decline.  Substantial cognitive decline over time cannot be explained by depression and most likely reflects incipient dementia.