Association between short-term PM1 exposure and cardiorespiratory diseases: Evidence from a systematic review and meta-analysis

Studies suggested that the smaller particle size has more adverse effects on cardiorespiratory diseases. However, the associations between PM1 (particulate matter with an aerodynamic diameter of ≤1 μm) and cardiorespiratory diseases remains unclear. Therefore, we conducted a meta-analysis to summarize and quantify the associations between short-term exposure to PM1 and morbidity and mortality of cardiovascular and respiratory diseases. Four databases (PubMed, Cochrane Library, Web of Science, and CNKI) were searched for articles published up to March 16, 2021. Meta-analysis was used to pool the effect estimates of PM1 on cardiovascular and respiratory diseases [i.e., relative risk (RR) with the 95% confidence interval (CI)]. Subgroup analysis were conducted based on the statistical analysis methods, disease subtypes, and pollutant models. Finally, 12 studies were included, and we observed significant associations between PM1 and both cardiovascular mortality (ER: 0.84%, 95%CI: 0.06%, 1.64%) and respiratory mortality (ER: 0.57%, 95%CI: 0.30%, 0.78%). However, a significant PM1-morbidity association was only found for total respiratory morbidity (ER: 2.60%, 95%CI: 1.00%, 4.30%). The results of the subgroup analysis showed that only the association between asthma and PM1 was significant (ER: 2.60%, 95%CI: 1.00%, 4.30%), and the risk based on the two-pollutant model was higher than that of the single-pollutant model. Considering the limited number of available studies, our findings should be proven in future studies involved in varying settings, disease subtypes, and advanced study designs.