Air quality improvement and incident dementia: Effects of observed and hypothetical reductions in air pollutant using parametric g‐computation

Abstract Introduction No evidence exists about the impact of air pollution reduction on incidence of dementia. The aim of this study was to quantify how air quality improvement leads to dementia‐incidence benefits. Methods In the French Three‐City cohort (12 years of follow‐up), we used parametric g‐computation to quantify the expected number of prevented dementia cases under different hypothetical interventions with particulate matter measuring <2.5 μm (PM 2.5 ) reductions. Results Among 7051 participants, 789 participants developed dementia. The median PM 2.5 reduction between 1990 and 2000 was 12.2 (μg/m 3 ). Such a reduction reduced the risk of all‐cause dementia (hazard ratio [HR], 0.85; 95% confidence interval [CI], 0.76 to 0.95). If all study participants were enjoying a hypothetical reduction of more than 13.10 μg/m 3 (median reduction observed in the city of Montpellier), the rate difference was −0.37 (95% CI, −0.57 to −0.17) and the rate ratio was 0.67 (95% CI, 0.50 to 0.84). Discussion These findings highlight the possible substantial benefits of reducing air pollution in the prevention of dementia.