Invited commentary: how exposure to air pollution may shape dementia risk, and what epidemiology can say about it.

The number of Americans with Alzheimer's disease (AD) dementia is expected to triple by 2050. No effective treatments exist, and prevention research has focused on behaviors and medical conditions, which have been difficult to modify at the population level. Cardiovascular disease epidemiology can inform the search for AD risk factors; exposure to fine particulate matter (PM) air pollution increases cardiovascular risk, pollutant regulations appear to reduce cardiovascular deaths, and vascular pathology influences dementia risk. In this issue of the Journal, Ailshire and Crimmins (Am J Epidemiol. 2014;180(4):359-366) report analyses of data from 14,000 older adults living across the United States, indicating an inverse association between exposure to PM and cognitive function, an outcome related to AD by virtue of the long period of cognitive decline that precedes clinical disease. Their work joins a growing body of data linking PM exposure to AD risk. If these data reflect causality, PM exposure would be 1 of few AD risk factors that are not only widespread, but that also can be modified at the population level using regulatory intervention. Active collaboration between air pollution and dementia epidemiologists will be critical for refining the available evidence and filling fundamental gaps, including the lack of studies on AD itself.