Associations between early-life exposure to PM_2.5and reductions in childhood lung function in two North American longitudinal pregnancy cohort studies

Background: Data integration of epidemiologic studies across different geographic regions can provide enhanced exposure contrast and statistical power to examine adverse respiratory effects of early-life exposure to particulate matter <2.5 microns in diameter (PM_2.5). Methodological tools improve our ability to combine data while more fully accounting for study heterogeneity. Methods: Analyses included children enrolled in two longitudinal birth cohorts in Boston, Massachusetts, and Mexico City. Propensity score matching using the 1:3 nearest neighbor with caliper method was used. Residential PM_2.5exposure was estimated from 2 months before 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, FEF_25-75%, and FEV₁/FVC. Using distributed lag nonlinear models, we examined associations between monthly averaged PM_2.5levels and lung function outcomes adjusted for covariates, in unmatched and matched pooled samples. Results: In the matched pooled sample, PM_2.5exposure between postnatal months 35-44 and 35-52 was associated with lower FEV₁and FVC z scores, respectively. A 5 µg/m³increase in PM_2.5was associated with a reduction in FEV₁z score of 0.13 (95% CI = -0.26, -0.01) and a reduction in FVC z score of 0.13 (95% CI = -0.25, -0.01). Additionally PM_2.5during postnatal months 23-39 was associated with a reduction in FEF_25-75%z score of 0.31 (95% CI = -0.57, -0.05). Conclusions: Methodological tools enhanced our ability to combine multisite data while accounting for study heterogeneity. Ambient PM_2.5exposure in early childhood was associated with lung function reductions in middle childhood.