Dementia and Alzheimer disease incidence: a prospective cohort study.
BACKGROUND
Age-specific incidence rates for dementia and Alzheimer disease (AD) are important for research and clinical practice. Incidence estimates for the United States are few and vary with the population sampled and study design; we present data that will contribute to a consensus of these rates.


OBJECTIVE
To provide age-specific incidence estimates for dementia and AD and to estimate the association of sex, educational level, and apolipoprotein E genotype with onset.


METHODS
Prospective cohort study; begun in 1994 with follow-up interviews every 2 years.


METHODS
Members of community-based, large health maintenance organization with demographics consistent with the surrounding base population; diagnostic evaluation by university-based study clinicians.


METHODS
Random sample of subjects aged 65 years or older from the base population; dementia free, nonnursing home residents. Of 5422 who were eligible, 2581 were enrolled, and 2356 had at least 1 follow-up evaluation (10 591 person-years of observation).


METHODS
Dementia and Alzheimer disease diagnoses were based on standard criteria. Age-specific incidence rates were calculated using a person-years approach with Poisson distribution confidence intervals. Cox proportional hazards model analysis was used to examine other factors.


RESULTS
Two hundred fifteen cases of dementia and 151 cases of AD were diagnosed. Incidence rates for dementia and AD increase across the 5-year age groups; AD rates rise from 2.8 per 1000 person-years (age group, 65-69 years) to 56.1 per 1000 person-years in the older than 90-year age group. The rates nearly triple from the 75-to-79-year and 80-to-84-year age groups, but the relative increase is much less thereafter. Sex was not associated with AD onset. Educational level (>15 years vs <12 years) was associated with a decreased risk of AD; however, the association was also dependent on the baseline cognitive screening test score.


CONCLUSIONS
Our dementia and AD incidence rates are consistent with recent US and European cohort studies, providing clinicians and researchers new information concerning the reproducibility of incidence estimates across settings. Increased risk was associated with age and the apolipoprotein E genotype; also with a low baseline cognitive screening test score. Educational level was inversely associated with the risk of dementia and positively associated with the baseline cognitive test score; thus, detection of AD by the screening test could also be influenced by educational level.
Kukull
Walter A
WA
National Alzheimer Coordinating Center, Department of Epidemiology, Box 357236, School of Public Health and Community Medicine, University of Washington, Seattle, WA 98195-7236, USA. kukull@u.washington.edu
Higdon
Roger
R
Bowen
James D
JD
McCormick
Wayne C
WC
Teri
Linda
L
Schellenberg
Gerard D
GD
van Belle
Gerald
G
Jolley
Lance
L
Larson
Eric B
EB
D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000175:diagnosis / Q000453:epidemiology* / Q000235:genetics; D001057:Apolipoproteins E / Q000235:genetics; D015331:Cohort Studies; D016001:Confidence Intervals; D003704:Dementia / Q000175:diagnosis / Q000453:epidemiology* / Q000235:genetics; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008297:Male; D016012:Poisson Distribution; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors
D001057:Apolipoproteins E