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

Background: Emerging evidence identifies ambient particulate matter (PM) with an aerodynamic diameter () as a modifiable risk factor for dementia, but the potential health benefits gained by enacting regulations that reduce remain unclear.

Objectives: Our aim was to estimate the total effects of hypothetical ambient 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 y of age at baseline (2010). We estimated the total effects of hypothetical ambient interventions (achieving annual average standards of , , and ) 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 per 1,000 population [95% confidence interval (CI): , ], per 1,000 population (95% CI: , ), per 1,000 population (95% CI: , ), with interventions achieving annual average standards of , , and , respectively.

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