Outdoor fine particles and nonfatal strokes: systematic review and meta-analysis
- DOI
- Language of the publication
- English
- Date
- 2014-09-03
- Type
- Article
- Author(s)
- Shin, Hwashin H.
- Fann, Neal
- Burnett, Richard T.
- Cohen, Aaron
- Hubbell, Bryan J.
- Publisher
- Lippincott, Williams & Wilkins
Abstract
Background: Epidemiologic studies find that long- and short-term exposure to fine particles (PM2.5) is associated with adverse cardiovascular outcomes, including ischemic and hemorrhagic strokes. However, few systematic reviews or meta-analyses have synthesized these results. Methods: We reviewed epidemiologic studies that estimated the risks of nonfatal strokes attributable to ambient PM2.5. To pool risks among studies we used a random-effects model and 2 Bayesian approaches. The first Bayesian approach assumes a normal prior that allows risks to be zero, positive or negative. The second assumes a gamma prior, where risks can only be positive. This second approach is proposed when the number of studies pooled is small, and there is toxicological or clinical literature to support a causal relation. Results: We identified 20 studies suitable for quantitative meta-analysis. Evidence for publication bias is limited. The frequentist meta-analysis produced pooled risk ratios of 1.06 (95% confidence interval = 1.00-1.13) and 1.007 (1.003-1.010) for long- and short-term effects, respectively. The Bayesian meta-analysis found a posterior mean risk ratio of 1.08 (95% posterior interval = 0.96-1.26) and 1.008 (1.003-1.013) from a normal prior, and of 1.05 (1.02-1.10) and 1.008 (1.004-1.013) from a gamma prior, for long- and short-term effects, respectively, per 10 μg/m PM2.5. Conclusions: Sufficient evidence exists to develop a concentration-response relation for short- and long-term exposures to PM2.5 and stroke incidence. Long-term exposures to PM2.5 result in a higher risk ratio than short-term exposures, regardless of the pooling method. The evidence for short-term PM2.5-related ischemic stroke is especially strong.
Plain language summary
Health Canada is responsible for conducting risk assessments of air pollution under the Clean Air Regulatory Agenda. One aspect of risk assessment is to examine the strength of the evidence of associations between exposure to outdoor air pollution and health outcomes by analysing information on health effects reported in the peer-reviewed literature. It has been suspected, but not confirmed, that both short-term (on the order of days) and long-term (on the order of years) exposure to outdoor air pollution increases the risk of stroke, a major adverse health outcome. Health Canada, in partnership with the United States Environmental Protection Agency, conducted an assessment of the strength of the evidence of such a relationship. After reviewing and conducting a mathematical synthesis of all the available evidence published in peer-reviewed scientific journals, it was concluded that exposure to air pollution, particularly fine particulate matter (PM2.5), was causally linked to an increased risk of stroke from both short- and long-term exposures, with the risk from long-term exposure being greater than that from short-term exposure. This evidence provides further support for the new, more stringent Canadian Ambient Air Quality Standards for fine particulate matter, which are aimed at supporting the provinces and territories taking actions to ensure that poor outdoor air quality improves and that good outdoor air quality is maintained.
Subject
- Health,
- Health and safety