Is Alzheimer’s disease inevitable with age?

Abstract

The unprecedented and growing number of older adults in the US and other developed countries has crystallized scientific interest in the health consequences of aging.Perhaps the most feared of these consequences is Alzheimer's disease (AD).As the leading cause of dementia, AD not only extracts a terrible toll from patients and their families but is an enormous public health burden, with annual costs in the US alone approaching 100 billion dollars.The major risk factor for AD is living longer; AD prevalence doubles every 5 years after age 65 and approaches 50% by age 85 (1).Some epidemiologists report that the prevalence of AD continues to increase in the very old and conclude that "AD ... may become universal when age is sufficiently advanced" (2).As we enter the 21st century with increasing life expectancies, the obvious question becomes, "If we live long enough, will we all be demented?"(3).Although this question cannot be definitely resolved at present, accumulating evidence suggests that not all of us will.Before reviewing the data that led me to consider aging and AD as discrete rather than continuous processes, I should acknowledge 3 biases.First, I believe that for studies of cognitive aging, longitudinal study designs are preferable to cross-sectional designs, which may be confounded by cohort effects that overestimate