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Research

Changes in exposure to ambient fine particulate matter after relocating and long term survival in Canada: quasi-experimental study

BMJ 2021; 375 doi: https://doi.org/10.1136/bmj.n2368 (Published 08 October 2021) Cite this as: BMJ 2021;375:n2368

Linked Editorial

Cut particulate air pollution, save lives
  1. Hong Chen, research scientist1234,
  2. Jay S Kaufman, professor56,
  3. Toyib Olaniyan, research analyst7,
  4. Lauren Pinault, senior research analyst7,
  5. Michael Tjepkema, principal researcher7,
  6. Li Chen, biologist1,
  7. Aaron van Donkelaar, research associate8,
  8. Randall V Martin, professor9,
  9. Perry Hystad, associate professor10,
  10. Chen Chen, postdoctoral researcher12,
  11. Megan Kirby-McGregor, doctoral student5,
  12. Li Bai, senior epidemiologist3,
  13. Richard T Burnett, senior research scientist1,
  14. Tarik Benmarhnia, associate professor1112
  1. 1Environmental Health Science and Research Bureau, Health Canada, Ottawa, ON, K1A 0K9, Canada
  2. 2Public Health Ontario, Toronto, ON, Canada
  3. 3ICES, Toronto, ON, Canada
  4. 4Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada
  5. 5Department of Epidemiology and Biostatistics, McGill University, Montreal, QC, Canada
  6. 6Institute for Health and Social Policy, McGill University, Montreal, QC, Canada
  7. 7Health Analysis Division, Statistics Canada, Ottawa, ON, Canada
  8. 8Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS, Canada
  9. 9Department of Energy, Environment and Chemical Engineering, Washington University, St Louis, MO, USA
  10. 10College of Public Health and Human Sciences, Oregon State University, Corvallis, OR, USA
  11. 11Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA, USA
  12. 12Department of Family Medicine and Public Health, University of California, San Diego, La Jolla, CA, USA
  1. Correspondence to: H Chen hong.chen{at}hc-sc.gc.ca
  • Accepted 27 September 2021

Abstract

Objective To investigate the association between changes in long term residential exposure to ambient fine particulate matter (PM2.5) and premature mortality in Canada.

Design Population based quasi-experimental study.

Setting Canada.

Participants 663 100 respondents to the 1996, 2001, and 2006 Canadian censuses aged 25-89 years who had consistently lived in areas with either high or low PM2.5 levels over five years preceding census day and moved during the ensuing five years.

Interventions Changes in long term exposure to PM2.5 arising from residential mobility.

Main outcome measures The primary outcome was deaths from natural causes. Secondary outcomes were deaths from any cardiometabolic cause, any respiratory cause, and any cancer cause. All outcomes were obtained from the national vital statistics database.

Results Using a propensity score matching technique with numerous personal, socioeconomic, health, and environment related covariates, each participant who moved to a different PM2.5 area was matched with up to three participants who moved within the same PM2.5 area. In the matched groups that moved from high to intermediate or low PM2.5 areas, residential mobility was associated with a decline in annual PM2.5 exposure from 10.6 μg/m3 to 7.4 and 5.0 μg/m3, respectively. Conversely, in the matched groups that moved from low to intermediate or high PM2.5 areas, annual PM2.5 increased from 4.6 μg/m3 to 6.7 and 9.2 μg/m3. Five years after moving, individuals who experienced a reduction in exposure to PM2.5 from high to intermediate levels showed a 6.8% (95% confidence interval 1.7% to 11.7%) reduction in mortality (2510 deaths in 56 025 v 4925 deaths in 101 960). A greater decline in mortality occurred among those exposed to a larger reduction in PM2.5. Increased mortality was found with exposure to PM2.5 from low to high levels, and to a lesser degree from low to intermediate levels. Furthermore, the decreases in PM2.5 exposure were most strongly associated with reductions in cardiometabolic deaths, whereas the increases in PM2.5 exposure were mostly related to respiratory deaths. No strong evidence was found for the changes in PM2.5 exposure with cancer related deaths.

Conclusions In Canada, decreases in PM2.5 were associated with lower mortality, whereas increases in PM2.5 were associated with higher mortality. These results were observed at PM2.5 levels considerably lower than many other countries, providing support for continuously improving air quality.

Footnotes

  • Contributors: HC conceived the study. HC, TB, and JSK contributed to the study design. LP and TO prepared and cleaned the data. AvD, RVM, and PH contributed to exposure assessment. HC, LC, TB, JSK, RTB, TO, and LP contributed to data analyses. HC took the lead in drafting the manuscript. All authors contributed to the interpretation of data, provided critical revisions to the manuscript, and approved the final draft. HC is the guarantor. HC had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. The corresponding author attests that all listed authors meet authorship criteria and that no others meeting the criteria have been omitted.

  • Funding: This study was funded by Health Canada (#810630). The funders had no role in considering the study design; the collection, analysis, or interpretation of data; the writing of the report; or the decision to submit the article for publication.

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/disclosure-of-interest/ and declare: support from funded by Health Canada for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

  • The lead author (HC) affirms that the manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.

  • Dissemination to participants and related patient and public communities: Findings will be disseminated via media outreach to the general public—for example, press releases by the media departments of the authors’ research institutes, and plain language publications in social media.

  • Provenance and peer review: Not commissioned; externally peer reviewed.

Data availability statement

Statistics Canada’s policy on data privacy and confidentiality prohibits the analytical cohorts used (1996, 2001, and 2006 CanCHEC) to be freely available in the manuscript, supplementary files, or in a public repository. However, access can be granted through Statistics Canada’s Research Data Centre program. The programs used to assign environmental exposures (PCCF+ and postal code imputation) are also available to researchers through subscription or request. Environmental exposures are available on request to the original authors of the data. The analytical code used was all standard R and SAS code (eg, matchit, mice, glm, coxph, data steps).

http://creativecommons.org/licenses/by-nc/4.0/

This is an Open Access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.

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