Individual and Joint Effects of Early-Life Ambient PM2.5 Exposure and Maternal Prepregnancy Obesity on Childhood Overweight or Obesity

Background: Although previous studies suggest that exposure to traffic-related pollution during childhood increases the risk of childhood overweight or obesity (COWO), the role of early life exposure to fine particulate matter (aerodynamic diameter <2.5μm; PM2.5) and its joint effect with the mother's prepregnancy body mass index (MPBMI) on COWO remain unclear. Objectives: The present study was conducted to examine the individual and joint effects of ambient PM2.5 exposures and MPBMI on the risk of COWO. Methods: We estimated exposures to ambient PM2.5 in utero and during the first 2 y of life (F2YL), using data from the U.S. Environmental Protection Agency’s (EPA's) Air Quality System matched to residential address, in 1,446 mother–infant pairs who were recruited at birth from 1998 and followed up prospectively through 2012 at the Boston Medical Center in Massachusetts. We quantified the individual and joint effects of PM2.5 exposure with MPBMI on COWO, defined as the child's age- and sex-specific BMI z-score ≥85th percentile at the last well-child care visit between 2 and 9 y of age. Additivity was assessed by estimating the reduced excess risk due to interaction. Results: Comparing the highest and lowest quartiles of PM2.5, the adjusted relative risks (RRs) [95% confidence intervals (CIs)] of COWO were 1.3 (95% CI: 1.1, 1.5), 1.2 (95% CI: 1.0, 1.4), 1.2 (95% CI: 1.0, 1.4), 1.3 (95% CI: 1.1, 1.6), 1.3 (95% CI: 1.1, 1.5) and 1.3 (1.1, 1.5) during preconception; the first, second, and third trimesters; the entire period of pregnancy; and F2YL, respectively. Spline regression showed a dose–response relationship between PM2.5 levels and COWO after a threshold near the median exposure (10.46μg/m3–10.89μg/m3). Compared with their counterparts, children of obese mothers exposed to high levels of PM2.5 had the highest risk of COWO [RR≥2.0, relative excess risk due to interaction (RERI) not significant]. Conclusions: In the present study, we observed that early life exposure to PM2.5 may play an important role in the early life origins of COWO and may increase the risk of COWO in children of mothers who were overweight or obese before pregnancy beyond the risk that can be attributed to MPBMI alone. Our findings emphasize the clinical and public health policy relevance of early life PM2.5 exposure. https://doi.org/10.1289/EHP261