title: Risk estimates of mortality attributed to low concentrations of ambient fine particulate matter in the Canadian community health survey cohort.
abstract: BACKGROUND
  Understanding the shape of the relationship between long-term exposure to ambient fine particulate matter (PM2.5) concentrations and health risks is critical for health impact and risk assessment. Studies evaluating the health risks of exposure to low concentrations of PM2.5 are limited. Further, many existing studies lack individual-level information on potentially important behavioural confounding factors.
  
  
  METHODS
  A prospective cohort study was conducted among a subset of participants in a cohort that linked respondents of the Canadian Community Health Survey to mortality (n = 299,500) with satellite-derived ambient PM2.5 estimates. Participants enrolled between 2000 and 2008 were followed to date of death or December 31, 2011. Cox proportional hazards models were used to estimate hazard ratios (HRs) for mortality attributed to PM2.5 exposure, adjusted for individual-level and contextual covariates, including smoking behaviour and body mass index (BMI).
  
  
  RESULTS
  Approximately 26,300 non-accidental deaths, of which 32.5 % were due to circulatory disease and 9.1 % were due to respiratory disease, occurred during the follow-up period. Ambient PM2.5 exposures were relatively low (mean = 6.3 μg/m(3)), yet each 10 μg/m(3) increase in exposure was associated with increased risks of non-accidental (HR = 1.26; 95 % CI: 1.19-1.34), circulatory disease (HR = 1.19; 95 % CI: 1.07-1.31), and respiratory disease mortality (HR = 1.52; 95 % CI: 1.26-1.84) in fully adjusted models. Higher hazard ratios were observed for respiratory mortality among respondents who never smoked (HR = 1.97; 95 % CI: 1.24-3.13 vs. HR = 1.45; 95 % CI: 1.17-1.79 for ever smokers), and among obese (BMI ≥ 30) respondents (HR = 1.76; 95 % CI: 1.15-2.69 vs. HR = 1.41; 95 % CI: 1.04-1.91 for normal weight respondents), though differences between groups were not statistically significant. A threshold analysis for non-accidental mortality estimated a threshold concentration of 0 μg/m(3) (+95 % CI = 4.5 μg/m(3)).
  
  
  CONCLUSIONS
  Increased risks of non-accidental, circulatory, and respiratory mortality were observed even at very low concentrations of ambient PM2.5. HRs were generally greater than most literature values, and adjusting for behavioural covariates served to reduce HR estimates slightly.
authors: Health Analysis Division, Statistics Canada, 100 Tunney's Pasture Driveway, Ottawa, ON, K1A 0T6, Canada. Lauren.Pinault@canada.ca.
authors: Lauren
authors: L
authors: Pinault
authors: Health Analysis Division, Statistics Canada, 100 Tunney's Pasture Driveway, Ottawa, ON, K1A 0T6, Canada. Michael.Tjepkema@canada.ca.
authors: Michael
authors: M
authors: Tjepkema
authors: New Brunswick Institute for Research, Data, and Training (NB-IRDT) and Department of Sociology, University of New Brunswick, Fredericton, NB, PO Box 4400, E3B 5A3, Canada. Dan.Crouse@unb.ca.
authors: Daniel L
authors: DL
authors: Crouse
authors: Air Health Effects Science Division, Health Canada, 269 Laurier Avenue West, Ottawa, ON, K1A 0K9, Canada. Scott.Weichenthal@hc-sc.gc.ca.
authors: Scott
authors: S
authors: Weichenthal
authors: Department of Physics and Atmospheric Science, Dalhousie University, 6310 Coburg Road, Halifax, NS, Canada. Aaron.Van.Donkelaar@gmail.com.
authors: Aaron
authors: A
authors: van Donkelaar
authors: Department of Physics and Atmospheric Science, Dalhousie University, 6310 Coburg Road, Halifax, NS, Canada. Randall.Martin@dal.ca.|Harvard-Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA, 02138, USA. Randall.Martin@dal.ca.
authors: Randall V
authors: RV
authors: Martin
authors: Faculty of Medicine/School of Population and Public Health, University of British Columbia, 2206 East Mall, Vancouver, BC, V6T 1Z3, Canada. Michael.Brauer@ubc.ca.
authors: Michael
authors: M
authors: Brauer
authors: Public Health Ontario, Suite 300, 480 University Avenue, Toronto, ON, M5G 1V2, Canada. Hong.Chen@oahpp.ca.
authors: Hong
authors: H
authors: Chen
authors: Environmental Health Science and Research Bureau, Health Canada, 50 Columbine Driveway, Ottawa, ON, Canada. Rick.Burnett@hc-sc.gc.ca.
authors: Richard T
authors: RT
authors: Burnett
mesh_terms: D000393:Air Pollutants / Q000009:adverse effects*; D000397:Air Pollution / Q000706:statistics & numerical data; D002170:Canada; D002318:Cardiovascular Diseases / Q000401:mortality*; D015331:Cohort Studies; D016208:Databases, Factual; D004781:Environmental Exposure / Q000009:adverse effects*; D006801:Humans; D052638:Particulate Matter / Q000009:adverse effects*; D011446:Prospective Studies; D012140:Respiratory Tract Diseases / Q000401:mortality*; D018570:Risk Assessment; D013223:Statistics as Topic; D013997:Time Factors
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter