Ambient air pollution and risk of incident dementia in older men living in a region with relatively low concentrations of pollutants: The Health in Men Study

Background: In areas with moderate to severe air pollution, pollutant concentrations are associated with dementia risk. It is unclear whether the same relationship is present in regions with lower ambient air pollution. Objective: To determine whether exposure to air pollution is associated with risk of incident dementia in general, and Alzheimer's disease and vascular dementia in particular, in older men living in a relatively low ambient air pollution region. Methods: The cohort comprised 11,243 men residing in Perth, Australia. Participants were aged ≥65 years and free of a dementia diagnosis at time of recruitment in 1996–1999. Incident dementia was identified from recruitment to 2018 via ICD diagnosis codes and subsequent study waves. Concentrations for three air pollutants, nitrogen dioxide (NO2), fine particulate matter less than 2.5 μm in diameter (PM2.5), and black carbon (BC) were estimated at participants’ home addresses using land-use regression models. We used Cox proportional hazards regression models adjusting for smoking status, physical activity, BMI, education, and socio-economic status. Results: Of 3053 (27.2%) incident cases of dementia, 1670 (54.7%) and 355 (11.6%) had documented Alzheimer's disease and vascular dementia. The average concentration of NO2 was 13.5 (SD 4.4) μg/m3, of PM2.5 was 4.54 (SD 1.6) μg/m3 and of BC was 0.97 (SD 0.29) ×10−5 m−1. None of the air pollutants were associated with incident dementia or Alzheimer's disease. In the unadjusted model, increased exposure to PM2.5 was associated with an increased risk of vascular dementia (for a 5 μg/m3 increase: HR 1.62, 95% CI 1.13, 2.31). However, this association was attenuated following adjustment for confounders (HR 1.39, 95% CI 0.93, 2.08). NO2 and BC were not associated with vascular dementia incidence. Discussion: Exposure to air pollution is not associated with increased risk of incident dementia in older men living in a region with relatively low ambient air pollution.