Hazed and Confused: The Effect of Air Pollution on Dementia.

This article investigates the causal impact of long-term exposure to fine particulate matter (PM2.5) on the probability of receiving a new diagnosis of Alzheimer's disease or related dementias among Americans aged 65 and older from 2001 to 2013. Utilizing quasi-random variation in PM2.5 exposure induced by the U.S. Environmental Protection Agency’s (EPA) Clean Air Act (CAA) nonattainment designations, the study employs instrumental variable methods and controls for potential confounders including baseline health, demographics, neighborhood characteristics, and survival selection. The findings indicate that a 1 µg/m³ increase in decadal PM2.5 exposure raises the probability of a new dementia diagnosis by approximately 2.15 percentage points, with larger effects observed among women, older individuals, and those with more clinical risk factors; notably, these effects persist below current regulatory thresholds. Extensive validation tests and sensitivity analyses support the robustness of the causal interpretation, highlighting air pollution as a significant and previously underappreciated risk factor for dementia.