Early life exposure to PM₂.₅ and lung function: A pooled analysis from two North American longitudinal pregnancy cohort studies

Background: Exposure to particulate matter <2.5 microns in diameter (PM₂.₅) produces pediatric respiratory morbidity. Lung development occurs in stages and the effects of PM₂.₅ may differ based on timing of exposure. Data integration of multiple epidemiologic studies can provide enhanced power and exposure contrast to examine associations between PM₂.₅ and respiratory outcomes. Aim: To combine data from two longitudinal cohorts while accounting for underlying heterogeneity and examine effects of early childhood PM₂.₅ exposure on lung function. Methods: Analyses included children from the Asthma Coalition on Community Environment and Social Stress Project in Boston, Massachusetts and the Programming Research in Obesity, Growth, Environment and Social Stressors study in Mexico City. Propensity scores were estimated from logistic models and 1-1 nearest neighbor matching method was used (n=300). Residential daily PM₂.₅ exposure was estimated from 2 months prior to birth to age 6 years using a validated satellite-based spatiotemporal model. Lung function was tested at ages 6-11 years and age, height, race and sex adjusted z-scores were estimated for FEV₁, FVC, FEF25-75% and FEV₁/FVC. Using distributed lag models, we examined associations between monthly averaged PM₂.₅ levels and lung function outcomes adjusting for maternal age, education, postnatal environmental tobacco smoke exposure and monthly temperature. Results: PM₂.₅ exposure between postnatal months 23-40 was associated with a lower FEV₁ z-score. A 5 µg/m³ increase in PM₂.₅ throughout this window was associated with a reduction in FEV₁ z-score of -0.36 (95% CI:-0.66, -0.05). Similarly, a 5 µg/m³ increase in PM₂.₅ throughout 18-39 months postnatal was associated with a reduction in FEF25-75% z-score of -0.56 (95% CI:-0.99, -0.14). Conclusions: Methodological tools enhanced our ability to combine multi-site data while accounting for study heterogeneity. Ambient PM₂.₅ exposure in early childhood was associated with an obstructive pattern on spirometry in middle childhood. Keywords: air pollution, respiratory, children’s health