Prevalence of cognitive impairment: data from the Indianapolis Study of Health and Aging.

BACKGROUND: The epidemiology and natural history of cognitive impairment that is not dementia is important to the understanding of normal aging and dementia.

OBJECTIVE: To determine the prevalence and outcome of cognitive impairment that is not dementia in an elderly African American population.

METHOD: A two-phase, longitudinal study of aging and dementia. A total of 2212 community-dwelling African American residents of Indianapolis, IN, aged 65 and older were screened, and a subset (n = 351) received full clinical assessment and diagnosis. Subsets of the clinically assessed were seen again for clinical assessment and rediagnosis at 18 and 48 months. Weighted logistic regression was used to generate age-specific prevalence estimates.

RESULTS: The overall rate of cognitive impairment among community-dwelling elderly was 23.4%. Age-specific rates indicate increasing prevalence with increasing age: 19.2% for ages 65 to 74 years, 27.6% for ages 75 to 84 years, and 38.0% for ages 85+ years. The most frequent cause of cognitive impairment was medically unexplained memory loss with a community prevalence of 12.5%, followed by medical illness-associated cognitive impairment (4.0% prevalence), stroke (3.6% prevalence), and alcohol abuse (1.5% prevalence). At 18-month follow-up, 26% (17/66) of the subjects had become demented.

CONCLUSIONS: Cognitive impairment short of dementia affects nearly one in four community-dwelling elders and is a major risk factor for later development of dementia.