Background The impact of ambient air pollution on stroke is well-documented. However, the modifying effect of obesity on the association is unclear. Recent research has proposed that obese individuals are more susceptible to the effects of air pollution. The objective is to systematically screen, appraise and synthesise the evidence examining modifying effects of obesity status on the association between air pollution and stroke.
Methods Databases searched include Scopus, PubMed and Web of Science. All empirical studies published in English between January 1st 1990 – March 30th 2019 were included for review. Data items were extracted using a standardised data extraction table. A narrative synthesis of the study results was completed. Included studies were quality assessed using the Joanna Briggs Institute and modified case-crossover appraisal tools. All evidence sourced were graded according to the Scottish Intercollegiate Guidelines Network (SIGN) level of evidence criteria.
Results Of 668 titles were identified, 218 had their full-text reviewed and seven met eligibility criteria. Five cohort studies (including a nest case-crossover), one cross-sectional study and one ecological study were included in the review. Findings across studies were limited. In summary, three studies found some evidence consistent with obesity worsening the association between air pollution and stroke. Inconsistencies in exposure used and measurement, outcome assessment, and data linkage methodology existed across studies. While the overall level of evidence assigned by the SIGN criteria was good, and the review included mainly high quality cohort studies with a low risk of confounding or bias, misclassification of exposure may be present.
Conclusion Some evidence exists to suggest modifying effects of obesity on the association between air pollution and stroke. However, evidence is very weak and hampered by different study designs and outcome assessments. Thus, further research using large, nationally representative studies with stringent outcomes and exposure measurement methods in addition to fixed linking methodology between air-pollution and health data are needed while continuing the appropriate adjustment for confounding factors.
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