Evidence for aging as the cause of Alzheimer's disease.

Part 1 presents the results of a meta-analytic study on the effects of aging on intelligence. Analysis of a total of 20 longitudinal samples shows that most of the intelligence scores rose before the age of 50 and fell at a progressively increasing rate after the age of 50. An equation describing this rise and fall in intelligence was derived. Part 2 shows the relationship between the predicted prevalence of Alzheimer's disease (from the equation derived in Part 1) and the prevalence of the disease obtained from 10 studies. The predictive curve fit so well with the observed prevalence data that the results can be interpreted as evidence that Alzheimer's is a manifestation of aging.