Associations between Gestational Exposure to Air Pollution and Maternal Vitamin D Levels

Abstract

BACKGROUND and AIM Individuals living in areas with higher air pollution have lower levels of vitamin D than residents of areas with lower pollution. Evidence suggests non-optimal gestational vitamin D as an important determinant of pregnancy and child health outcomes. We investigated the association between gestational exposure to air pollution and maternal vitamin D levels. METHODS Participants were 16,553 pregnant women from birth cohorts in the UK (BiB), US (Project Viva), Netherlands (ABCD and Generation R), Poland (REPRO_PL), and Spain (INMA). Averaged concentrations of air pollutants from conception until vitamin D measurement were estimated at participants’ residential addresses using land-use regression or other spatiotemporal models. Cohorts measured 25-hydroxy vitamin D [25(OH)D] and/or 25(OH)D3 in serum or plasma at early or mid-pregnancy. We performed linear regression models in each cohort to estimate the association between air pollution exposure and vitamin D levels and pooled cohort-specific results in a random-effect meta-analysis. Models were adjusted for sociodemographic characteristics, smoking and alcohol use, parity, body mass index, and month of conception. RESULTS Concentrations of nitrogen dioxide and fine PM (PM2.5) were lower and had less variation in Project Viva and BiB than other cohorts. In REPRO_PL, 95% of women had vitamin D<20 ng/ml; this rate was 85% in BiB, 52% in Generation R, and <50% in other cohorts. We found an inverse association between PM2.5 and vitamin D levels (-1.4 ng/mL, 95%CI:-2.6,-0.2, per 5 μg/m3 increase in PM2.5). Heterogeneity was high among cohorts, with associations driven by ABCD, BiB, and INMA. There was no association between nitrogen oxide exposure and vitamin D levels. CONCLUSIONS PM2.5 exposure might contribute to non-optimal levels of vitamin D in pregnancy. Future studies should focus on underlying mechanisms, including biological pathways, e.g., inducing metabolism of vitamin D, or other factors, e.g., reduced outdoor activity. KEYWORDS: 25(OH)D; PM2.5; pregnancy; women