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Short term exposure to air pollution and stroke: systematic review and meta-analysis

BMJ 2015; 350 doi: (Published 24 March 2015) Cite this as: BMJ 2015;350:h1295

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  1. Anoop S V Shah, clinical lecturer in cardiology1,
  2. Kuan Ken Lee, core medical trainee1,
  3. David A McAllister, senior lecturer in epidemiology2,
  4. Amanda Hunter, specialist trainee in cardiology1,
  5. Harish Nair, senior research fellow in epidemiology2,
  6. William Whiteley, MRC clinician scientist and consultant neurologist3,
  7. Jeremy P Langrish, clinical lecturer in cardiology1,
  8. David E Newby, professor of cardiology1,
  9. Nicholas L Mills, reader in cardiology and consultant cardiologist.1
  1. 1BHF/University Centre for Cardiovascular Science, University of Edinburgh, Edinburgh EH16 4SB, UK
  2. 2Centre of Population Health Sciences, University of Edinburgh, Edinburgh, UK
  3. 3Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, UK
  1. Correspondence to: A S V Shah anoopsshah{at}
  • Accepted 5 February 2015


Objective To review the evidence for the short term association between air pollution and stroke.

Design Systematic review and meta-analysis of observational studies

Data sources Medline, Embase, Global Health, Cumulative Index to Nursing and Allied Health Literature (CINAHL), and Web of Science searched to January 2014 with no language restrictions.

Eligibility criteria Studies investigating the short term associations (up to lag of seven days) between daily increases in gaseous pollutants (carbon monoxide, sulphur dioxide, nitrogen dioxide, ozone) and particulate matter (<2.5 µm or <10 µm diameter (PM2.5 and PM10)), and admission to hospital for stroke or mortality.

Main outcome measures Admission to hospital and mortality from stroke.

Results From 2748 articles, 238 were reviewed in depth with 103 satisfying our inclusion criteria and 94 contributing to our meta-estimates. This provided a total of 6.2 million events across 28 countries. Admission to hospital for stroke or mortality from stroke was associated with an increase in concentrations of carbon monoxide (relative risk 1.015 per 1 ppm, 95% confidence interval 1.004 to 1.026), sulphur dioxide (1.019 per 10 ppb, 1.011 to 1.027), and nitrogen dioxide (1.014 per 10 ppb, 1.009 to 1.019). Increases in PM2.5 and PM10 concentration were also associated with admission and mortality (1.011 per 10 μg/m3 (1.011 to 1.012) and 1.003 per 10 µg/m3 (1.002 to 1.004), respectively). The weakest association was seen with ozone (1.001 per 10 ppb, 1.000 to 1.002). Strongest associations were observed on the day of exposure with more persistent effects observed for PM2·5.

Conclusion Gaseous and particulate air pollutants have a marked and close temporal association with admissions to hospital for stroke or mortality from stroke. Public and environmental health policies to reduce air pollution could reduce the burden of stroke.

Systematic review registration PROSPERO-CRD42014009225.


  • Contributors: ASVS and KKL contributed equally. ASVS conceived and designed the study. ASVS, KKL, and AH acquired the data. ASVS, KKL, DM, DEN, and NLM analysed and interpreted the data. ASVS, DEN, DM, and NLM drafted the initial manuscript. All authors made critical revisions of the manuscript for important intellectual content and approved the final version of the report. ASVS is guarantor.

  • Funding: This study was funded by a British Heart Foundation programme grant (RG/10/9/28286). ASVS, DEN, and NLM were supported by a British Heart Foundation clinical research scholarship (SS/CH/09/002), intermediate fellowship (FS/10/024/28266), chair award (CH/09/002), and programme grant (RG/10/9/28286), respectively. The sponsor of the study had no role in study design, data collection, data analysis, data interpretation, or writing of the report.

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at and declare: 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.

  • Ethical approval: Not required.

  • Data sharing: No additional data available.

  • Transparency: The lead author, (the manuscript’s guarantor), 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.

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