PM2.5 and Dementia in a Low Exposure Setting: The Influence of Odor Identification Ability and APOE

Background: Growing evidence show that long term exposure to air pollution increases the risk of dementia. Objective: The aim of this study was to investigate associations between PM2.5 exposure and dementia in a low exposure area, and to investigate the role of olfaction and the APOE epsilon 4 allele in these associations. Methods: Data were drawn from the Betula project, a longitudinal study on aging, memory, and dementia in Sweden. Odor identification abilitywas assessed using the Scandinavian Odor Identification Test (SOIT). Annual meanPM2.5 concentrations were obtained from a dispersion-model and matched at the participants' residential address. Proportional hazard regression was used to calculate hazard ratios. Results: Of 1,846 participants, 348 developed dementia during the 21-year follow-up period. The average annual mean PM2.5 exposure at baseline was 6.77 mu g/m(3), which is 1.77 mu g/m(3) above the WHO definition of clean air. In a fully adjusted model (adjusted for age, sex, APOE, SOIT, cardiovascular diseases and risk factors, and education) each 1 mu g/m(3) difference in annual mean PM2.5-concentration was associated with a hazard ratio of 1.23 for dementia (95% CI: 1.01-1.50). Analyses stratified by APOE status (epsilon 4 carriers versus non-carriers), and odor identification ability (high versus low), showed associations only for epsilon 4 carriers, and for low performance on odor identification ability. Conclusion: PM2.5 was associated with an increased risk of dementia in this low pollution setting. The associations between PM2.5 and dementia seemed stronger in APOE carriers and those with below average odor identification ability.