Incidence of AD may decline in the early 90s for men, later for women: The Cache County study
Miech, Richard A., J. C. S. Breitner, P.P. Zandi, A.S. Khachaturian, J.C. Anthony, and L. Mayer. 2002. "Incidence of AD may decline in the early 90s for men, later for women: The Cache County study." Neurology, 58(2): 209-218.
Objectives: To characterize the incidence of AD among the elderly population of Cache County, UT, noted for its longevity and high response rates; to explore sex differences; and to examine whether AD incidence plateaus or declines in extreme old age.Methods: Using a multistage screening process in 1998 and 1999, and reexamining 122 individuals who had been identified 3 years earlier as cognitively compromised but not demented, the authors found 185 individuals with incident dementia (123 with AD) among 3,308 participants who contributed 10,541 person-years of observation. Adjusting for nonresponse and screening sensitivity, the authors estimated the incidence of dementia and of AD for men and women in 3-year age intervals. Multivariate discrete time survival analysis was used to examine influences of age, sex, education, and genotype at APOE, as well as interactions of these factors.Results: The incidence of both dementia and AD increased almost exponentially until ages 85 to 90, but appeared to decline after age 93 for men and 97 for women. A statistical interaction between age and the presence of two APOE-e4 alleles indicated acceleration in onset of AD with this genotype; the interaction of age and one e4 suggested more modest acceleration. A statistical interaction of sex and age indicated greater incidence of AD in women than in men after age 85.Conclusions: The incidence of AD in the Cache County population increased with advancing age, but then peaked and declined among the extremely old. The presence of APOE-e4 alleles accelerated onset of AD, but did not appreciably alter lifetime incidence apparent over a span of 100 years.