Long-term exposure to ambient air pollution and risk of dementia: Results of the prospective Three-City Study: Epidemiology: Effects of air pollution on cognition

International audienceBackground:Chronic exposure to air pollution (AP) is associated with cardiovascular morbidity and mortality. Emerging epidemiological evidence suggests a relationship between exposure to various air pollutants (fine particulate matter (PM2.5), ozone (O3), and nitrogen dioxide (NO2)) and dementia. However, most of existing studies relied on population-based health administrative databases to obtain a dementia diagnosis. In a large French population-based cohort (the Three-City Study) and using state-of-the-art models for AP exposure, we aimed at assessing the effects of different air pollutants on dementia risk using reliable diagnosis tools.Methods:Participants aged ≥65 years were recruited between 1999 and 2001 and followed for 12 years. At baseline and every 2 years, dementia diagnoses were preliminary made using DSM-IV criteria and validated by an adjudication committee. Levels of NO2, O3, Black Carbon and PM2.5 were obtained at the residential addresses of participants using land-use regression models developed for Europe in the ELAPSE project (de Hoogh et al., Env Int 120 (2018) 81-92). For each year of follow-up, we estimated for each subject a 10-year moving window of mean past exposure to each pollutant. We used a Cox Proportional Hazard model where exposure to AP was included as a time-varying variable. Analyses were adjusted for individual (age, sex, education, APOE4 genotype, vascular risk factors, depression, respiratory diseases) and contextual (neighborhood’s deprivation index) level confounders.Result:At baseline, the mean (SD) age of the 7956 participants was 73.2 (5.4) years-old. Sixty-one percent of them were women. The mean time of follow-up was 9.2 (3.6) years. Over the follow-up period, the mean annual PM2.5 levels ranged from 15 to 33 µg/m3 and 910 participants developed dementia. We observed a positive association between levels of PM2.5 and dementia risk [HR=1.16, 95%CI (1.02-1.32) for a 5µg/m3 increase in PM2.5]. We did not observe any relationship between exposure to the other air pollutants and dementia risk.Conclusion:In this large cohort with reliable diagnosis of dementia and individual estimates of AP exposure, we observed that long-term exposure to PM2.5 was associated with higher dementia incidence. These results suggest that PM2.5 exposure might be a modifiable risk factor of dementia