INCREASED exposure to ambient PM2.5 and NO2 is associated with a modestly increased risk of incident adult asthma, while no significant relationship was found for O3, and evidence for SO2 remains insufficient. These findings highlight the potential role of air pollution in adult asthma development but require cautious interpretation due to study heterogeneity.
Ambient air pollution is an established risk factor for childhood asthma, but its impact on adult-onset asthma is less well understood. To address this gap, a systematic review and meta-analysis was conducted to evaluate associations between specific pollutants, including PM2.5, NO2, O3, and SO2, and the risk of new-onset asthma in adults. Observational studies reporting incident asthma in individuals aged 18 or older and exposure metrics for these pollutants were included. Quality assessment was conducted using the Newcastle–Ottawa scale, and meta-analysis was applied for pollutants with data from at least four studies.
Out of 1891 identified references, 25 studies met the inclusion criteria for the systematic review. Meta-analyses were performed for PM2.5 (nine studies), NO2 (nine studies), and O3 (four studies). A 5 μg/m³ increase in PM2.5 was associated with a pooled relative risk (RR) of 1.07 (95% CI 1.01 to 1.13), and a 10 μg/m³ increase in NO2 was associated with a pooled RR of 1.11 (1.03 to 1.20). For O3, no significant association with asthma risk was observed (pooled RR 1.04 [0.79 to 1.36] per 60 μg/m³ increase). Substantial heterogeneity was observed (I² = 88% across analyses), with meta-regression indicating that average exposure levels contributed to heterogeneity in NO2 studies (95% CI –0.0077 to –0.0025 per μg/m³).
These findings suggest that air pollution, particularly PM2.5 and NO2, may contribute to adult-onset asthma, highlighting the need for further investigation. Future research should aim for harmonised methodologies to address heterogeneity and improve confidence in pooled estimates. Clinicians should consider environmental exposures as part of adult asthma risk assessment, while public health measures targeting pollution reduction could have significant implications for asthma prevention.
Abigail Craig, EMJ
Reference
Lee S et al. Ambient air pollution exposure and adult asthma incidence: a systematic review and meta-analysis. Lancet Planet Health. 2024;8(12):e1065-e1078.
