Associations between early-life exposure to PM2.5 and reductions in childhood lung function in two North American longitudinal pregnancy cohort studies.

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_2.5 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, FEF_25-75%, and FEV₁/FVC. Using distributed lag nonlinear models, we examined associations between monthly averaged PM_2.5 levels and lung function outcomes adjusted for covariates, in unmatched and matched pooled samples.

Results: In the matched pooled sample, PM_2.5 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 PM_2.5 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 PM_2.5 during 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_2.5 exposure in early childhood was associated with lung function reductions in middle childhood.