Air pollution and maternal vitamin D Status: Critical time window identification and ultraviolet radiation-mediated pathways.

Background: Maternal vitamin D deficiency (VDD) is a global health concern, with air pollution emerging as a potential risk factor. However, the underlying mechanisms, particularly the mediating role of Ultraviolet Radiation (UVR), remain poorly understood. This study investigated the impact of air pollution exposure, including PM chemical components, on 25-hydroxyvitamin D [25(OH)D] status in pregnant women, focusing on the mediating role of UVR.

Methods: A prospective cohort of 2258 pregnant women in Henan, China, was established. Average air pollutants and UVR exposure from the last menstrual period to the day before blood sampling were estimated using Kriging interpolation. VDD was defined as 25(OH)D concentrations below 30 nmol/L. Linear and logistic regression models assessed associations among air pollution, UVR, and 25(OH)D status. Dose-response relationships were modeled using restricted cubic spline functions, distributed lag nonlinear models (DLNM) were applied to identify critical exposure windows. Mediation analysis quantified the proportion of the air pollution effect on 25(OH)D levels and VDD risk mediated by UVR.

Results: Exposure to most air pollutants demonstrated significant negative correlations with serum 25(OH)D concentrations (PM: β = -0.95, 95 %CI: 1.32, -0.59) and positive associations with VDD risk (PM: OR = 1.13, 95 %CI: 1.09, 1.17). Through DLNM, we identified critical exposure windows at 5-6-week lags where PM, PM, and sulfate components exerted maximum effects on 25(OH)D reduction, exhibiting identical temporal response patterns. Mediation analysis demonstrated that UVR accounted for 92.51 % of the inverse association between black carbon exposure and 25(OH)D levels.

Conclusions: Air pollution may impair maternal vitamin D status by reducing UVR availability.