Dementia incidence may increase more slowly after age 90: results from the Bronx Aging Study.
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.
Hall
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CB
Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, NY, USA. chall@aecom.yu.edu
Verghese
J
J
Sliwinski
M
M
Chen
Z
Z
Katz
M
M
Derby
C
C
Lipton
R B
RB
D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000473:pathology*; D015984:Causality; D015331:Cohort Studies; D003704:Dementia / Q000175:diagnosis / Q000453:epidemiology* / Q000503:physiopathology; D018450:Disease Progression; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D009483:Neuropsychological Tests; D009519:New York City / Q000453:epidemiology; D012307:Risk Factors; D017678:Sex Distribution; D011795:Surveys and Questionnaires