We extend the reasoning commonly applied to the understanding of chron
ic diseases and their prevention to Alzheimer's disease and other deme
nting disorders. The highly visible progress in finding genetic bases
of Alzheimer's disease may leave a large proportion of cases unexplain
ed. Rather, both genetic susceptibility and environmental factors are
demonstrably important for disease expression. Thus, the research and
health policy implication would be to target resources toward identify
ing and modifying environmental risk factors that might delay or preve
nt dementia.