Association between air pollution and cardiovascular mortality in China: a systematic review and meta-analysis

Air pollutant levels in many Chinese cities remained significantly higher than the upper limits stated in World Health Organization guidelines. In light of limited evidence in China, we conducted a meta-analysis summarizing the association between acute exposure of air pollution and cardiovascular mortality. We searched PubMed, and CNKI databases etc. for literature published in English or Chinese up to January 2017. Outcomes were pooled and compared using random-effects model. Excess risks (ERs) per 10 μg/m³ increase in PM_2.5, PM₁₀, NO₂, SO₂ and O₃ were evaluated. Subgroup analysis was conducted according to lag patterns (lags 0, 1, 2, 0-1, 0-2 days), gender (male vs. female), temperature (cool vs. warm) and age (< 65 vs. ≥ 65). Study bias was detected using Begg's and Egger's test. Of 299 articles identified, 30 met inclusion criteria. Each 10 μg/m³ increase in the concentration was associated with a higher incidence of cardiovascular mortality for PM_2.5 (0.68%, 95% CI: 0.39-0.97%), PM₁₀ (0.39%, 95% CI: 0.26-0.53%), NO₂ (1.12%, 95% CI: 0.76-1.48%), SO₂ (0.75%, 95% CI: 0.42-1.09%), and O₃ (0.62%, 95% CI: 0.33-0.92%), respectively. Air pollution conferred greater adverse impacts on cardiovascular mortality for longer duration of exposures. Strongest associations were seen for lag 0-1 day of exposure among all pollutants. Female, lower temperature, and age > 65 years were associated with greater risks of cardiovascular mortality for all pollutants. Higher concentrations of air pollutants correlated with a greater short-term increase in cardiovascular mortality. Further high-quality studies in China are urgently warranted to determine the susceptible population, which would offer reference for policy-making to minimize adverse health effects.