Meta-analysis on correlations between short-term exposures to 6 common air pollutants and incidence of ischemic stroke

Background Previous studies using meta-analysis to explore the relationship between air pollution exposure and ischemic stroke (IS) mostly focus on particulate matter-related themes, few include gaseous pollutants in the study, and subgroup analyses of factors such as different lag days, seasons, and genders are rarely been reported.

Objective To quantitatively evaluate the relationships between short-term exposures to 6 common air pollutants, including fine particulate matter (PM_2.5), inhalable particulate matter (PM₁₀), carbon monoxide (CO), nitrogen dioxide (NO₂), sulfur dioxide (SO₂), and ozone (O₃), and the incidence of IS.

Methods A systematic search was conducted to collect literature studying the 6 common air pollutants and IS published up to May 1, 2022 in 6 databases (China Journal Full-text Database, China Biology Medicine Disc, PubMed, Cochrane Library, Web of Science, and Embase). Literature quality evaluation was performed using the Newcastle-Ottawa Scale. Stata 16.0 software was used to conduct meta-analysis including heterogeneity test, combined effect size, meta-regression, subgroup analysis, sensitivity analysis, and publication bias test.

Results A total of 33 articles were qualified for inclusion. The total number of samples included in the literature was 7195631. The meta-analysis results showed that short-term exposures to PM_2.5 (OR=1.0082, 95%CI: 1.0049−1.0116), PM₁₀ (OR=1.0017, 95%CI: 1.0008−1.0026), CO (OR=1.0328, 95%CI: 1.0231−1.0426), NO₂ (OR=1.0150, 95%CI: 1.0079−1.0222), SO₂ (OR=1.0158, 95%CI: 1.0078-1.0238), and O₃ (OR=1.0017, 95%CI: 1.0003−1.0032) were associated with an increased risk of IS. PM₁₀ and O₃ increased the risk of IS in both lag0 and lag1, while PM_2.5, CO, NO₂, and SO₂ all showed an associated increased risk of IS only in lag0. The results of sensitivity analysis showed stable results for all pollutants studied, and there was no publication bias in the literature on the association of the remaining five pollutants with IS incidence except for the PM_2.5-related literature.

Conclusion Short-term exposures to PM_2.5, PM₁₀, CO, NO₂, SO₂, and O₃ may increase the incidence of IS, with this risk showing the most significant level on the day of IS onset.