Depression and risk of cognitive decline and Alzheimer's disease

BACKGROUND: Depression may be associated with cognitive decline in elderly people with impaired cognition. AIMS: To investigate whether depressed elderly people with normal cognition are at increased risk of cognitive decline and Alzheimer's disease. METHODS: Two independent samples of older people with normal cognition were selected from the community-based Amsterdam Study of the Elderly (AMSTEL) and the Longitudinal Aging Study Amsterdam (LASA). In AMSTEL, depression was assessed by means of the Geriatric Mental State Schedule. Clinical diagnoses of incident Alzheimer's disease were made using a two-step procedure. In LASA, depression was assessed with the Center for Epidemiologic Studies Depression Scale. Cognitive decline was defined as a drop of > or = 3 on the Mini-Mental State Examination at follow-up. RESULTS: Both in the AMSTEL and the LASA sample, depression was associated with an increased risk of Alzheimer's disease and cognitive decline, respectively, but only in subjects with higher levels of education. CONCLUSIONS: In a subgroup of more highly educated elderly people, depression may be an early manifestation of Alzheimer's disease before cognitive symptoms become apparent.