Ambient Air Pollution Exposure is Associated with the Infant Gut Microbiota

BACKGROUND AND AIM: Exposure to ambient air pollutants (AAP) has been linked with the gut microbiome in young adults; however, this relationship has not been studied in infancy. This study aimed to examine the relationships between AAP and the infant gut microbiota. METHODS: This study included 105 infants from the Southern California Mother’s Milk Study. Average exposure to particulate matter (PM2.5, PM10) and nitrogen dioxide (NO2), was examined during the first 6 months of life. The infant gut microbiota was characterized using 16S rRNA sequencing at 6 months. Associations between AAP and the composition of the gut microbiota was examined using a Zero Inflated Poisson Regression (ZIPR), where incidence risk ratios (IRR) and Bonferroni adjusted p-values are reported. Compositionally aware, multinomial models were used to describe associations between AAP and the abundance of each gut microbe, and new methods for visualizing those associations were used to identify an important subset of associated taxa. Based on a directed acyclic graph, models adjusted for sex, breastfeeding frequency, socioeconomic status, birthweight and infant age. RESULTS:Overall, 26, 16 and 22 gut bacterial taxa were associated with exposure to PM10, PM2.5 and NO2, respectively. For example, PM10 and PM2.5 were associated with Enterococcus (IRR=1.08, p0.001) and Actinomyces (IRR=1.46, p0.001) abundances, respectively. Multinomial analysis also revealed that PM10 exposure was associated with the composition of the gut microbiota based on the log-ratio of differentially ranked taxa sub-groups (R2=0.28, p0.001). For example, all microbial genera positively associated with PM10 via ZIPR were also classified as being in the top 35% of differentially ranked taxa positively associated with PM10 exposure. CONCLUSIONS:Early postnatal exposure to AAP was associated with the composition of the infant gut microbiota at 6-months of age. These results suggest that early life exposure to AAP may impact the developing gut microbiome, which may have important implications for infant development. KEYWORDS: Air pollution, Microbiome, Outcomes, Particulate matter, Oxides of nitrogen, Children's environmental health