Ambient pollutants, gestational parent diet factors, and risk of preterm birth in North Carolina
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Toxicological work suggests gestational parent (GP) diet may modify the effect of ambient pollutants on birth outcomes. We assessed risk of preterm birth in humans in relation to fine particulate matter (PM2.5), ozone (O3), and nitrogen dioxide (NO2) and whether associations vary by diet. Participants comprised 684 gestational parent-singleton infant pairs in the Newborn Epigenetics Study prospective birth cohort in central NC with data on GP diet, gestational age at birth, and residence at birth. Total energy intake, percent of energy intake from saturated fat, and percent of energy intake from total fat derived from a food frequency questionnaire were dichotomized at the 75th percentile. We assigned exposures from previously validated pollutant prediction models and residence at birth across trimesters. We used log binomial regressions to estimate risk ratio (RR) for preterm birth by pollutant interquartile ranges, including pollutant-diet interaction terms. We assessed departure from additivity using interaction contrast ratios (ICRs). The fully adjusted model controlled for age of GP at birth, pre-pregnancy body mass index, GP race/ethnicity, GP education, season of conception, household income during gestation, and each diet factor. We addressed missing covariate data with multiple imputation. Point estimates suggest that O3 may be protective against preterm birth when exposure occurs in trimester 2 (min RR: 0.72, 95% CI: 0.34, 1.52), but may be harmful when exposure occurs in trimester 3 (max RR: 1.23, 95% CI: 0.53, 3.10). Additionally, PM2.5 may be protective when adjusted for total fat and saturated fat in trimester 2. ICRs suggest departure from additivity with some pollutant-diet combinations. While confidence intervals are wide, we observed potential associations with preterm birth across different pollutants and time periods and pollutant-diet combinations.