Change in cognitive function in older persons from a community population: relation to age and Alzheimer disease.

OBJECTIVE To examine change in cognitive function in older persons sampled from a community population, and its relation to age and Alzheimer disease. DESIGN Prospective cohort study with an average of 3.5 years of follow-up. SETTING East Boston, Mass--a geographically defined, urban, working-class community. PARTICIPANTS A stratified, random sample of persons 65 years and older underwent uniform, structured clinical evaluation for Alzheimer disease. The 388 persons (89.2% of those eligible) who completed at least 1 annual follow-up evaluation were studied: 97 had Alzheimer disease at baseline; 95 developed Alzheimer disease during the study; and 196 were unaffected. OUTCOME MEASURES Eight cognitive performance tests were administered, then converted to population-weighted z scores and averaged to create a composite summary measure of cognitive function. Initial level of and change in this score were the outcome measures. RESULTS In the population as a whole, many persons experienced a decline in cognitive performance, and age was related to both initial level and rate of decline. Analyses were conducted in 3 subgroups: persons with Alzheimer disease at baseline, those who developed Alzheimer disease during the study, and those who remained unaffected. In both Alzheimer disease subgroups, substantial cognitive decline was observed, but neither initial level nor rate of decline was related to age. In unaffected persons, little cognitive decline was evident, and there was a small, inverse association of age with initial level of cognitive function. CONCLUSION In a general population sample, there was little evidence of cognitive decline during a 3.5-year period among persons who remained free of Alzheimer disease.