Influence of PM₁ exposure on total and cause-specific respiratory diseases: a systematic review and meta-analysis

An increasing number of studies examined the potential effects of PM₁ (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 PM₁ 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/m³ increase in PM₁, 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 I² value of 87%, 70%, and 0%, respectively. Subgroup analyses showed that long-term exposure to PM₁ was associated with increased risk of asthma (OR 1.47, 95% CI 1.33-1.63) with an I² value of 0%, while short-term exposure to PM₁ was not associated with asthma (OR 1.07, 95% CI 0.89-1.27) with the I² 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 PM₁ may increase morbidity in total and cause-specific respiratory diseases in the population.