The potential effect modifying role of nutrition, physical activity, and body mass index on the association between air pollution and adverse birth and early-life health outcomes: a scoping review

Background. Air pollution is a prominent contributor to the burden of adverse birth and early child health outcomes. However, considerable heterogeneity of impacts has been observed, which may be due to limited exploration of key effect modifiers. This scoping review was conducted to synthesize evidence on the potential effect modifying roles of nutrition, physical activity, and body mass index (BMI) on the associations between early-life air pollution exposures and adverse birth and early-life health outcomes. Methods. PubMed, Web of Science, and Scopus databases were systematically searched for relevant studies through July 2023. Studies were included if they were conducted amongst pregnant women or individuals between 0-17 years, provided empirical evidence on associations between air pollution exposure and adverse birth and/or early-childhood health outcomes, and conducted effect modification-related analyses by maternal (i.e., in-utero) or early childhood nutrition, physical activity, or BMI. Data from selected studies were abstracted and summarized based on study design, population characteristics, and the exposures, outcomes, and effect modifiers assessed. Results. A total of 13 studies were included; 10 were cohort studies, and 3 were cross-sectional studies. All but one of the studies explored the impact of ambient air pollutants (particulate matter, nitrogen dioxide, ozone, ultra-fine particles, elemental carbon, and black carbon) prenatally or in early life on adverse birth (preterm birth, birth weight, low birth weight) and early childhood outcomes (childhood obesity). Effect modifiers examined included pre-pregnancy BMI (n = 5 studies), maternal and child dietary characteristics (n = 7 studies), and child physical activity patterns (n = 2 studies). Discussion. Evidence for effect modification, although present, was inconsistent and weak. Consideration should be given to exploring effect modification of air pollution-related impacts to help explain heterogeneity of associations observed across populations, a key knowledge gap limiting public health messaging strategies.