Chemical constituents of PM and their association with childhood asthma and lung function: a systematic review and meta-analysis.

UNLABELLED

Over the past decades, a growing body of research has explored the associations between various chemical constituents of fine particulate matter (PM) and childhood asthma. However, findings have been largely inconsistent. This study aims to synthesize evidence on the impact of short- and long-term exposure to PM chemical constituents on asthma risk and lung function changes in children and adolescents. The study protocol has been registered on PROSPERO (CRD 42024562521). We systematically searched for articles on the associations between the black carbon (BC), organic carbon (OC), ammonium (NH), nitrate (NO), sulfate (SO), and heavy metals in PM and the risk of asthma and lung function (forced vital capacity [FVC], forced expiratory volume in one second [FEV1], etc.) published up to January 2025, throughout databases of the Web of Science, MEDLINE, PubMed, and EMBASE. The overall effect size (OR: odds ratio; or SMD: standard mean difference) with a 95% confidence interval (CI) was calculated using a random-effect model. Heterogeneity among the research findings was assessed using the I-squared (I) statistic. A total of 24 original studies with a sample size of 6,978,265 were included. Twelve studies focused on long- and 12 on short-term associations. The inter-quartile range (IQR) values for BC, OC, SO, NO, and NH in PM were 0.61, 1.68, 4.23, 3.48, and 1.38 μg/m, respectively. For the long-term association, every IQR increase of OC, NH, and BC was associated with 37% (pooled OR = 1.370), 28.5% (pooled OR = 1.285), and 7.4% (pooled OR = 1.074) higher risk of childhood asthma; every IQR increase of BC and SO was associated with reduced FEV1 (SMD: 0.068 L and 0.639 L) and FVC (SMD: 0.144 L and 0.479 L). Every IQR increase of BC exposure was associated with reduced FEV1 (SMD: 0.061 L) and PEF (SMD: 0.130 L). Short-term exposure to SO, NH, NO, BC, Fe, and Zn was also associated with higher asthma admissions with no significant heterogeneity.

CONCLUSION

Long-term and short-term exposures to BC, OC, and NH are the main contributing chemical constituents in PM for childhood asthma. BC and SO are the main contributors for reduced lung function in children and adolescents.

WHAT IS KNOWN

• PM2.5 impacts respiratory health, but which specific component most harms asthma and lung function of children remains unclear.

WHAT IS NEW

• This systematic review and meta-analysis found that black and organic carbon, as well as ammonium, mainly contributed to increased asthma risk, while black carbon and sulfate in PM2.5 were key factors for reduced lung function in children.