Early-life exposure to submicron particulate air pollution in relation to asthma development in Chinese preschool children.

Abstract Background Emerging research suggested an association of early-life particulate air pollution exposure with development of asthma in childhood. However, the potentially differential effects of submicron particulate matter (PM1) remain largely unknown. Objective This study primarily aimed to investigate associations of childhood asthma and wheezing with in-utero and first-year exposures to size-specific particles. Methods We conducted a large cross-sectional survey among 5788 preschool children aged 3–5 years in central China. In-utero and first-year exposures to ambient PM1, PM2.5 and PM10 at 1×1 km-resolution were assessed using machine learning based spatiotemporal models. A time-to-event analysis was performed to examine associations between residential PM exposures and childhood onset of asthma and wheezing. Results Early-life size-specific PM exposures, particularly during pregnancy, were significantly associated with increased risk of asthma, while no evident PM-wheezing associations were observed. Each 10 μg/m3 increase of in-utero and first-year PM1 exposure was accordingly associated with an asthma’s hazard ratio (HR) in childhood of 1.618 (95% confidence interval: 1.159–2.258, p=0.005) and 1.543 (0.822–2.896, p=0.177). Subgroup analyses suggest that short breastfeeding duration may aggravate PM-associated risk of childhood asthma. Each 10 μg/m3 increase of in utero exposure to PM1, for instance, was associated with a HR of 2.260 (1.393–3.666) among children with 0–5 months’ breastfeeding and 1.156 (0.721–1.853) among those longer breastfed. Conclusion Our study added comparative evidence for increased risk of childhood asthma in relation to early-life PM exposures, highlighting stronger associations with ambient PM1 than PM2.5 and PM10.