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Dementia incidence may increase more slowly after age 90

Results from the Bronx Aging Study

From the Einstein Aging Study (Drs. Hall, Verghese, Derby, and Lipton, and M. Katz), Departments of Epidemiology and Population Health (Drs. Hall, Derby, and Lipton) and Neurology (Drs. Hall, Verghese, Derby, and Lipton, and M. Katz), Albert Einstein College of Medicine, Bronx, NY; Department of Psychology (Dr. Sliwinski), Syracuse University, Syracuse, NY; and Department of Biostatistics and Epidemiology (Dr. Chen), University of Pennsylvania, Philadelphia.

Address correspondence and reprint requests to Dr. Charles B. Hall, Department of Epidemiology and Population Health, 1300 Morris Park Avenue, Bronx, NY 10462; e-mail: chall{at}aecom.yu.edu

Background: Dementia incidence increases dramatically from age 65 to age 85, with many studies reporting a doubling every 5 years. The incidence beyond age 85 is not established.

Objective: To estimate the incidence of dementia as a function of age, with a particular focus on persons aged 85 and over.

Methods: The Bronx Aging Study began in 1980 with 488 healthy, nondemented community-dwelling individuals, age 75 to 85. Persons in the study received clinical examinations and cognitive testing approximately every 12 months until death or loss to follow-up. The diagnosis of dementia was made using Diagnostic and Statistical Manual of Mental Disorders-III-R at diagnostic case conferences. Dementia incidence rates were calculated for 5-year age bands using person-time of follow-up as the denominator.

Results: The relative incidence rate ratios of dementia for age 80 to 84 vs 75 to 79 was 2.32 (95% CI 1.23 to 4.37), the relative rate for age 85 to 89 vs 80 to 84 was 1.89 (95% CI 1.26 to 2.83), the relative rate for age 90 to 94 vs 85 to 89 was 1.49 (95% CI 0.86 to 2.58), while the relative rate for age 95 to 99 vs 90 to 94 was 1.31 (95% CI 0.38 to 4.46). Similar results were seen for men and women considered separately. Had the rate of increase from age 75 to 89 continued into the 90s, the study would have had 73% power to detect a significant difference between the rates for age 90 to 94 and 85 to 89 given the amount of observed follow-up time.

Conclusions: Whereas dementia incidence continues to increase beyond age 85, the rate of increase appears to slow relative to that of 65- to 85-year-olds. These results suggest that dementia in the oldest old might be related not to the aging process itself but with age-associated risk factors.

The Einstein Aging Study is supported by a National Institutes on Aging program project grant (AGO3949-15).

Disclosure: The authors report no conflicts of interest.

Received February 2, 2005. Accepted in final form June 7, 2005.

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