Association Between Air Pollution Exposure and Risk of Hemorrhagic Stroke: A Systematic Review and Meta-analysis

Air pollution has been associated with multisystem health adversities. However, the association between short-term air pollution and hemorrhagic stroke has not been sufficiently evaluated in recent years. Considering that hemorrhagic stroke has a high incidence rate (28.8% of incident strokes) and accounts for almost 7.2 million deaths per year globally, it is important to identify risk factors and use it to guide preventative measures.

A systematic search was conducted on 4 databases (Embase, OVID Medline, Web of Science, PubMed). Studies selected for review included time series, case-crossover, and cohort studies, published in English, from all time periods, and investigated the risk of hemorrhagic stroke after exposure to air pollution (particulate matter ≤ 2.5 μm in diameter [PM_2.5], particulate matter ≤ 10 μm in diameter [PM₁₀], nitrogen dioxide [NO₂], sulfur dioxide [SO₂], ozone [O₃], or carbon monoxide [CO]). Data for different risk outcomes (risk ratio, odds ratio) were meta-analyzed using an inverse variance statistical analysis and random effects model.

Among the 2435 studies identified, 31 were included and deemed eligible for review and meta-analysis. The results illustrated a statistically significant increase in the risk of hemorrhagic stroke per 10 μg/m³ increase in NO₂ exposure (risk ratio, 1.0142; 95% confidence interval, 1.0000-1.0286; P = 0.05), and CO exposure (odds ratio, 1.0008; 95% confidence interval, 1.0000-1.0016; P = 0.05).

Among the 6 air pollutants studied, NO₂ and CO exposure was associated with a statistically significant increase in the risk of hemorrhagic stroke. This can help guide effective preventative protocols and public health measures in an effort to reduce the burden of cardiovascular and cerebrovascular disease.