Long-term exposure to ultrafine particles and mortality from neurodegenerative diseases: a population-based cohort study

Background: Transportation and industrial activities emit large quantities of air pollutants, including unregulated ultrafine particles (UFP, <0.1 um), which may adversely affect brain health. Methods: We analyzed data from 2.1 million adults in the Canadian Census Health and Environment Cohorts (CanCHECs) living in Montreal and Toronto (2001-2019). Vital status and primary cause of death were obtained from the Canadian Vital Statistics- Death database. We assigned high-resolution estimates of UFP number concentrations and UFP size to participants’ residential postal codes using three-year moving averages. Cox proportional hazards models were used to estimates hazard ratios (HRs) between long-term outdoor UFP number concentrations and mortality from dementia, Parkinson’s disease, and amyotrophic lateral sclerosis. We further examined associations by dementia sub-types including Alzheimer’s disease, vascular dementia and unspecified dementia. Models were used with and without inverse probability of censoring weights for competing events, and adjusted for UFP size, sociodemographic factors, and co-pollutants. Findings: Over 19 million person-years, we identified 20,560 deaths from neurodegenerative diseases. Each 10,000 particle/cm 3 increase in UFP number concentrations was associated with increased dementia mortality (HR = 1.22, 95% CI: 1.17–1.27), with stronger associations observed after adjusting for UFP size. Positive associations were observed for all dementia subtypes, with the largest for vascular dementia (HR = 1.49, 95% CI: 1.27–1.76). We did not observe effects of UFP on mortality from Parkinson’s disease or amyotrophic lateral sclerosis. Interpretation: Long-term exposure to outdoor UFPs may contribute to mortality from specific neurodegenerative diseases, particularly dementia. Reducing population exposures to these unregulated pollutants could help mitigate the burden of neurodegenerative mortality.