Associations of gestational exposure to air pollution with maternal vitamin D levels: a meta-analysis

Context: Maternal vitamin D level is an important determinant of pregnancy and child health outcomes. Exposure to air pollution is suspected to increase the risk of vitamin D deficiency, but the evidence is scarce. Objective: We investigated the association between air pollution during pregnancy and maternal vitamin D levels. Methods: A total of 15 935 pregnant women from 5 birth cohorts in Europe and the United States were included. Averaged concentrations of nitrogen oxides, fine and coarse particles, and composition of fine particles from conception until vitamin D measurement were estimated at participants' residential addresses using land-use regression or other spatiotemporal models. Cohorts measured vitamin D as 25(OH)D or 25(OH)D₃ levels in serum or plasma at early or mid-pregnancy. We defined suboptimal vitamin D levels as levels below 20 ng/mL. We performed logistic regression models for each cohort to estimate the association between air pollution exposure and suboptimal vitamin D levels and pooled cohort-specific estimates in a random-effect meta-analysis. Models were adjusted for sociodemographic and lifestyle characteristics and month of conception. Results: We found an association between particulate matter (PM)_2.5 and higher odds of suboptimal vitamin D levels (ie, below 20 ng/mL) (odds ratio per 5 μg/m³ increase in PM_2.5, 1.43; 95% CI: 1.02, 1.99). There was no association between other air pollutant exposure and vitamin D levels. Conclusion: PM_2.5 exposure might contribute to suboptimal levels of vitamin D in pregnancy. Reducing air pollution exposure should be a priority because vitamin D deficiency may adversely influence offspring development.