Associations between early-life exposure to PM2.5 and 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 (PM2.5). 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 PM2.5 exposure 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, FEF25–75%, and FEV1/FVC. Using distributed lag nonlinear models, we examined associations between monthly averaged PM2.5 levels and lung function outcomes adjusted for covariates, in unmatched and matched pooled samples. Results: In the matched pooled sample, PM2.5 exposure between postnatal months 35–44 and 35–52 was associated with lower FEV1 and FVC z scores, respectively. A 5 µg/m3 increase in PM2.5 was associated with a reduction in FEV1 z 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 PM2.5 during postnatal months 23–39 was associated with a reduction in FEF25–75% 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 PM2.5 exposure in early childhood was associated with lung function reductions in middle childhood.