Particulate matter may have a limited influence on maternal vitamin D levels.

Evidence for an association between the amount of particulate matter (PM) in the atmosphere and vitamin D status of pregnant women is limited. We aimed to examine the independent association between PM and maternal levels of serum 25-hydroxyvitamin D (25OHD) during the second trimester and to explore possible modifications to the association by meteorological factors. 27,768 pregnant women presenting for prenatal examination who were tested for serum 25OHD concentration during the second trimester between January 1, 2016, and December 31, 2020, were included in this retrospective analysis. Exposure to PM was evaluated based on daily average PM with an aerodynamic diameter of ≤ 2.5 μm (PM 2.5 ) and PM with an aerodynamic diameter of ≤ 10 μm (PM 10 ). Corresponding meteorological data for daily average atmospheric temperature, atmospheric pressure, relative humidity, sunshine duration, and wind speed were collected. The maximum cumulative effects of PM 2.5 occurred at lag 45 days, and the maximum cumulative effects of PM 10 occurred at lag 60 days. In crude models, 45-day moving daily average PM 2.5 concentrations were negatively associated with 25OHD levels (β, - 0.20; 95% CI - 0.21 to - 0.19), as were 60-day moving daily average PM 10 concentrations (β, - 0.14; 95% CI - 0.15 to - 0.14). After adjusting for temporal and meteorological factors, the effect values were drastically reduced (adjusted β of PM 2.5 , - 0.032; 95% CI - 0.046 to - 0.018; adjusted β of PM 10 , - 0.039; 95% CI - 0.049 to - 0.028). Our study showed there was a small, independent, negative association between PM in the atmosphere and maternal serum 25OHD levels during the second trimester of pregnancy after adjusting for temporal and/or meteorological factors, which indicates that PM may have a limited influence on maternal serum 25OHD levels. Besides taking vitamin D supplements, pregnant women should keep participating in outdoor activities while taking PM protection measures to improve their vitamin D levels when PM levels are high in winter and spring.