Influence of PM 1 exposure on total and cause-specific respiratory diseases: a systematic review and meta-analysis

An increasing number of studies examined the potential effects of PM 1 (submicronic particulate matter with an aerodynamic diameter ≤ 1 μm) on the risk of respiratory diseases; however, the results have been inconclusive. This study aimed to determine the overall association between PM 1 with total and cause-specific respiratory diseases. A systematic review and meta-analysis was conducted with 68 related articles retrieved, and six articles met the full inclusion criteria for the final analysis. For a 10 μg/m 3 increase in PM 1 , the pooled odds ratio ( OR ) was 1.05 (95% CI 0.98–1.12) for total respiratory diseases, 1.25 (95% CI 1.00–1.56) for asthma, and 1.07 (95% CI 1.04–1.10) for pneumonia with the I 2 value of 87%, 70%, and 0%, respectively. Subgroup analyses showed that long-term exposure to PM 1 was associated with increased risk of asthma ( OR 1.47, 95% CI 1.33–1.63) with an I 2 value of 0%, while short-term exposure to PM 1 was not associated with asthma ( OR 1.07, 95% CI 0.89–1.27) with the I 2 value of 0%. Egger’s test showed that publication bias existed ( P = 0.041); however, the funnel plot was symmetrical with the inclusion of the moderator. In conclusion, elevated levels of PM 1 may increase morbidity in total and cause-specific respiratory diseases in the population.