Long-term effect of fine particulate matter on hospitalization with dementia

New evidence suggests that particulate matter less than 2.5 μm in diameter (PM_2.5) is associated with late-onset dementia (LOD). However, epidemiological studies for the entire population are lacking.

We analyzed approximately 94 million follow-up records from fee-for-service Medicare records for 13 million Medicare beneficiaries residing in the southeastern United States (U.S.) from 2000 to 2013. We used spatially and temporally continuous PM_2.5 exposure data. To account for time-varying PM_2.5 levels, we applied an Andersen-Gill counting process proportional hazard model; we stratified our analyses by subtype of dementia and level of urbanization of residence.

During a median follow-up of 6 years, 1,409,599 hospitalizations with dementia occurred. The adjusted hazard ratio (HR) of hospitalization with dementia was 1.049 (95% confidence interval [CI], 1.048 to 1.051) per 1 μg/m³ increase in annual PM_2.5. The hazard ratio for vascular dementia was higher (HR, 1.086; 95% CI, 1.082 to 1.090). In large, the magnitude of the effect grew as the level of urbanization increased (HR, 1.036; 95% CI, 1.031 to 1.041 in rural areas versus HR, 1.052; 95% CI, 1.050 to 1.054 in metropolitan areas).

Long-term exposure to higher PM_2.5 was associated with increased hospitalizations with dementia.