Parathyroid hormone mediates the adverse impact of air pollution exposure on serum 25-hydroxyvitamin D: A nationwide cross-sectional study in China

Background: Maintaining normal levels of 25-hydroxyvitamin D [25(OH)D] and parathyroid hormone (PTH) is crucial for preserving skeletal health. However, evidence regarding the associations of exposure to air pollution with serum 25(OH)D and PTH were limited and ambiguous. Hence, the objective of this cross-sectional study was to systematically evaluate the association between air pollution [particulate matter <= 2.5 mu m (PM2.5) and ozone (O3)] exposure and serum 25(OH)D and PTH levels in males aged 50 and above and postmenopausal female. Materials and methods: This study is multicenter, cross-sectional study within the framework of the ongoing China Community-based Cohort of Osteoporosis. The 1-year-average PM2.5 and O3 exposures prior to the baseline survey were estimated using random forest models with relatively high accuracy. Multiple linear regression models were employed to assess the associations between PM2.5 and O3 concentrations with the serum levels of 25(OH)D and PTH. Furthermore, mediation analysis was performed to scrutinize the potential mediating role of PTH in the interplay between PM2.5, O3, and serum 25(OH)D. Results: A total of 13194 participants were included. Our analysis showed that every 10 mu g/m3 increase in the 1year average PM2.5, were associated with -0.32 units (95% CI: 0.48, -0.17) of change in the 25(OH)D and 0.15 units (95% CI: 0.11, 0.19) of change in the PTH, respectively. Every 10 mu g/m3 increase in the 1-year average O3, were associated with -0.78 units (95% CI: 1.05, -0.51) of change in the 25(OH)D and 0.50 units (95% CI: 0.43, 0.57) of change in the PTH, respectively. Estimates of the mediation ratio indicated that increased PTH mediated a 50.48% negative correlation between PM2.5 exposure and circulating 25(OH)D level. Increased PTH mediated 69.61% of the negative effects of O3 exposure on circulating 25(OH)D level. Conclusions: Exposure to PM2.5 and O3 significantly diminished 25(OH)D while elevating PTH levels. Notably, the elevated PTH concentration partially mediates the associations between PM2.5 and O3 exposure and 25(OH)D level.