Abstract
BACKGROUND: Emerging evidence identifies ambient particulate matter (PM) with an aerodynamic diameter ≤ 2.5 μm (PM2.5) as a modifiable risk factor for dementia, but the potential health benefits gained by enacting regulations that reduce PM2.5 remain unclear. OBJECTIVES: Our aim was to estimate the total effects of hypothetical ambient PM2.5 interventions starting in late life on the risk of dementia in a cohort using the parametric g-formula. METHODS: We used data from 291,495 participants in the UK Biobank cohort who were free of dementia and ≥ 55 y of age at baseline (2010). We estimated the total effects of hypothetical ambient PM2.5 interventions (achieving annual average standards of 12 μg/m3, 10 μg/m3, and 9 μg/m3) from 2010 to 2019 on the risk of dementia by calculating the difference between the estimated 10-y risk of dementia under a specified hypothetical intervention and the risk under no intervention using the parametric g-formula. RESULTS: In comparison with no intervention, the estimated 10-y risk difference of dementia was - 0.54 per 1,000 population [95% confidence interval (CI): - 1.00, - 0.10], - 1.36 per 1,000 population (95% CI: - 2.44, - 0.25), - 1.92 per 1,000 population (95% CI: - 3.39, - 0.33), with PM2.5 interventions achieving annual average standards of 12 μg/m3, 10 μg/m3, and 9 μg/m3, respectively. DISCUSSION: The estimated 10-y risk of dementia decreased if the individual ambient PM2.5 exposure was reduced due to more stringent PM2.5 standards in late life in comparison with the natural course without intervention on ambient PM2.5 exposure. Our findings, obtained using the parametric g-formula-a causal inference method that can directly evaluate the impact of hypothetical interventions-suggest that policies reducing ambient PM2.5 pollution may lower the risk of dementia among UK Biobank participants who would experience more stringent ambient PM2.5 standards in late life. https://doi.org/10.1289/EHP14723.