Age-specific incidence rates of Alzheimer's disease: the Baltimore Longitudinal Study of Aging.
OBJECTIVE
To estimate age-specific incidence rates of AD in the Baltimore Longitudinal Study of Aging (BLSA).


BACKGROUND
The BLSA is a volunteer cohort of normal subjects followed longitudinally with biennial evaluations at the Gerontology Research Center of the National Institute on Aging.


METHODS
Subjects are 1236 participants (802 men, 434 women) in the BLSA with longitudinal follow-up between January 1985 and May 1998. The average length of follow-up was 7.5 years, with participants evaluated every 2 years by physical, neurologic, and neuropsychological examinations. Using Diagnostic and Statistical Manual of Mental Disorders, 3rd ed., revised and National Institute of Neurological and Communicative Disorders and Stroke-Alzheimer's Disease and Related Disorders Association criteria, the authors diagnosed dementia and AD.


RESULTS
The authors diagnosed 155 cases of dementia, of which 114 (74%) were AD. Incidence rates of AD increased with age from an estimated 0.08% per year (95% CI 0.00 to 0.43) in the 60 to 65 age group to an estimated 6.48% per year (95% CI 5.01 to 8.38) in the 85+ age group for men and women combined. The doubling time of incidence rates was estimated to be approximately 4.4 years and the median time of conversion from mild cognitive impairment to diagnosis of AD was estimated to be 4.4 years. There was a trend for women to have higher incidence rates than men and for fewer years of education to be associated with higher incidence rates; however, these effects were not significant.


CONCLUSIONS
Incidence rates for AD in the BLSA are consistent with published rates in other studies. The longitudinally followed subjects of the BLSA offer a unique opportunity to prospectively investigate the antecedents of AD.
Kawas
C
C
Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21224, USA.
Gray
S
S
Brookmeyer
R
R
Fozard
J
J
Zonderman
A
A
D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D000544:Alzheimer Disease / Q000175:diagnosis / Q000453:epidemiology*; D015142:Baltimore / Q000453:epidemiology; D015331:Cohort Studies; D005260:Female; D006801:Humans; D016015:Logistic Models; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D016017:Odds Ratio; D016012:Poisson Distribution