title: Living near major roads and the incidence of dementia, Parkinson's disease, and multiple sclerosis: a population-based cohort study.
abstract: Emerging evidence suggests that living near major roads might adversely affect cognition. However, little is known about its relationship with the incidence of dementia, Parkinson's disease, and multiple sclerosis. We aimed to investigate the association between residential proximity to major roadways and the incidence of these three neurological diseases in Ontario, Canada.
  
  
  
  In this population-based cohort study, we assembled two population-based cohorts including all adults aged 20-50 years (about 4·4 million; multiple sclerosis cohort) and all adults aged 55-85 years (about 2·2 million; dementia or Parkinson's disease cohort) who resided in Ontario, Canada on April 1, 2001. Eligible patients were free of these neurological diseases, Ontario residents for 5 years or longer, and Canadian-born. We ascertained the individual's proximity to major roadways based on their residential postal-code address in 1996, 5 years before cohort inception. Incident diagnoses of dementia, Parkinson's disease, and multiple sclerosis were ascertained from provincial health administrative databases with validated algorithms. We assessed the associations between traffic proximity and incident dementia, Parkinson's disease, and multiple sclerosis using Cox proportional hazards models, adjusting for individual and contextual factors such as diabetes, brain injury, and neighbourhood income. We did various sensitivity analyses, such as adjusting for access to neurologists and exposure to selected air pollutants, and restricting to never movers and urban dwellers.
  
  
  
  Between 2001, and 2012, we identified 243 611 incident cases of dementia, 31 577 cases of Parkinson's disease, and 9247 cases of multiple sclerosis. The adjusted hazard ratio (HR) of incident dementia was 1·07 for people living less than 50 m from a major traffic road (95% CI 1·06-1·08), 1·04 (1·02-1·05) for 50-100 m, 1·02 (1·01-1·03) for 101-200 m, and 1·00 (0·99-1·01) for 201-300 m versus further than 300 m (p for trend=0·0349). The associations were robust to sensitivity analyses and seemed stronger among urban residents, especially those who lived in major cities (HR 1·12, 95% CI 1·10-1·14 for people living <50 m from a major traffic road), and who never moved (1·12, 1·10-1·14 for people living <50 m from a major traffic road). No association was found with Parkinson's disease or multiple sclerosis.
  
  
  
  In this large population-based cohort, living close to heavy traffic was associated with a higher incidence of dementia, but not with Parkinson's disease or multiple sclerosis.
  
  
  
  Health Canada (MOA-4500314182).
authors.affiliation: Public Health Ontario, Toronto, ON, Canada; Institute for Clinical Evaluative Sciences, Toronto, ON, Canada; Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada. Electronic address: hong.chen@oahpp.ca.
authors.forename: Hong
authors.initials: H
authors.lastname: Chen
authors.affiliation: Public Health Ontario, Toronto, ON, Canada; Institute for Clinical Evaluative Sciences, Toronto, ON, Canada; Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada; Department of Family and Community Medicine, University of Toronto, Toronto, ON, Canada.
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Kwong
authors.affiliation: Public Health Ontario, Toronto, ON, Canada; Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada.
authors.forename: Ray
authors.initials: R
authors.lastname: Copes
authors.affiliation: Institute for Clinical Evaluative Sciences, Toronto, ON, Canada; Department of Family and Community Medicine, University of Toronto, Toronto, ON, Canada.
authors.forename: Karen
authors.initials: K
authors.lastname: Tu
authors.affiliation: Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada; Department of Health Sciences, Carleton University, Ottawa, ON, Canada.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Villeneuve
authors.affiliation: Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS, Canada.
authors.forename: Aaron
authors.initials: A
authors.lastname: van Donkelaar
authors.affiliation: College of Public Health and Human Sciences, Oregon State University, Corvallis, USA.
authors.forename: Perry
authors.initials: P
authors.lastname: Hystad
authors.affiliation: Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS, Canada; Harvard-Smithsonian Centre for Astrophysics, Cambridge, MA, USA.
authors.forename: Randall V
authors.initials: RV
authors.lastname: Martin
authors.affiliation: Division of Neurology, Department of Medicine, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, Canada.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Murray
authors.affiliation: Population Studies Division, Health Canada, Ottawa, ON, Canada.
authors.forename: Barry
authors.initials: B
authors.lastname: Jessiman
authors.affiliation: Institute for Clinical Evaluative Sciences, Toronto, ON, Canada.
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Wilton
authors.affiliation: Institute for Clinical Evaluative Sciences, Toronto, ON, Canada.
authors.forename: Alexander
authors.initials: A
authors.lastname: Kopp
authors.affiliation: Population Studies Division, Health Canada, Ottawa, ON, Canada.
authors.forename: Richard T
authors.initials: RT
authors.lastname: Burnett
mesh_terms: D000328:Adult; D000368:Aged; D015331:Cohort Studies; D003704:Dementia / Q000453:epidemiology*; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D018986:Motor Vehicles; D009103:Multiple Sclerosis / Q000453:epidemiology*; D009864:Ontario / Q000453:epidemiology; D010300:Parkinson Disease / Q000453:epidemiology*; D016016:Proportional Hazards Models; D012111:Residence Characteristics; D014505:Urban Population / Q000706:statistics & numerical data*; D055815:Young Adult