Association between exposure to ambient air pollution and hospital admission, incidence, and mortality of stroke: an updated systematic review and meta-analysis of more than 23 million participants

Previous studies have suggested that exposure to air pollution may increase stroke risk, but the results remain inconsistent. Evidence of more recent studies is highly warranted, especially gas air pollutants. We searched PubMed, Embase, and Web of Science to identify studies till February 2020 and conducted a meta-analysis on the association between air pollution (PM , particulate matter with aerodynamic diameter less than 2.5 μm; PM , particulate matter with aerodynamic diameter less than 10 μm; NO , nitrogen dioxide; SO , sulfur dioxide; CO, carbon monoxide; O , ozone) and stroke (hospital admission, incidence, and mortality). Fixed- or random-effects model was used to calculate pooled odds ratios (OR)/hazard ratio (HR) and their 95% confidence intervals (CI) for a 10 μg/m increase in air pollutant concentration. A total of 68 studies conducted from more than 23 million participants were included in our meta-analysis. Meta-analyses showed significant associations of all six air pollutants and stroke hospital admission (e.g., PM : OR = 1.008 (95% CI 1.005, 1.011); NO : OR = 1.023 (95% CI 1.015, 1.030), per 10 μg/m increases in air pollutant concentration). Exposure to PM , SO , and NO was associated with increased risks of stroke incidence (PM : HR = 1.048 (95% CI 1.020, 1.076); SO : HR = 1.002 (95% CI 1.000, 1.003); NO : HR = 1.002 (95% CI 1.000, 1.003), respectively). However, no significant differences were found in associations of PM , CO, O , and stroke incidence. Except for CO and O , we found that higher level of air pollution (PM , PM , SO , and NO ) exposure was associated with higher stroke mortality (e.g., PM : OR = 1.006 (95% CI 1.003, 1.010), SO : OR = 1.006 (95% CI 1.005, 1.008). Exposure to air pollution was positively associated with an increased risk of stroke hospital admission (PM , PM , SO , NO , CO, and O ), incidence (PM , SO , and NO ), and mortality (PM , PM , SO , and NO ). Our study would provide a more comprehensive evidence of air pollution and stroke, especially SO and NO .