Estimating the Effects of Hypothetical Ambient PM2.5 Interventions on the Risk of Dementia Using the Parametric g-Formula in the UK Biobank Cohort.

Abstract

Background: Emerging evidence identifies ambient particulate matter (PM) with an aerodynamic diameter $\le 2.5\mu m$ (${\mathrm{PM}}_{2.5}$) as a modifiable risk factor for dementia, but the potential health benefits gained by enacting regulations that reduce ${\mathrm{PM}}_{2.5}$ remain unclear.

Objectives: Our aim was to estimate the total effects of hypothetical ambient ${\mathrm{PM}}_{2.5}$ 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 $\ge 55$ y of age at baseline (2010). We estimated the total effects of hypothetical ambient ${\mathrm{PM}}_{2.5}$ interventions (achieving annual average standards of $12{\mu g/m}^3$, $10{\mu g/m}^3$, and $9{\mu g/m}^3$) 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 ${\mathrm{PM}}_{2.5}$ interventions achieving annual average standards of $12{\mu g/m}^3$, $10{\mu g/m}^3$, and $9{\mu g/m}^3$, respectively.

Discussion: The estimated 10-y risk of dementia decreased if the individual ambient ${\mathrm{PM}}_{2.5}$ exposure was reduced due to more stringent ${\mathrm{PM}}_{2.5}$ standards in late life in comparison with the natural course without intervention on ambient ${\mathrm{PM}}_{2.5}$ 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 ${\mathrm{PM}}_{2.5}$ pollution may lower the risk of dementia among UK Biobank participants who would experience more stringent ambient ${\mathrm{PM}}_{2.5}$ standards in late life. https://doi.org/10.1289/EHP14723.