Abstract
INTRODUCTION: Cadmium (Cd) exposure poses a significant risk to pregnant women. Given that vitamin D status and calcium intake are modifiable factors known to influence cadmium body burden, understanding how to optimize these factors to reduce cadmium burden in pregnancy is of significant public health importance. METHODS: Data from 1,054 pregnant women were extracted from the National Health and Nutrition Examination Survey (NHANES) for 2001–2018 and 2021–2023. Multivariable linear regression and restricted cubic splines (RCS) were used to examine associations between 25(OH)D and blood Cd levels. We tested the interaction effect of serum 25(OH)D and dietary calcium intake on reducing blood cadmium using Wald statistic, simple-slope analysis (± 1 SD), and Johnson-Neyman technique. RESULTS: An inverse relationship was observed between the natural log-transformed 25(OH)D [ln-25(OH)D] and Cd [ln-Cd] values, with a regression coefficient of -0.248 (95% CI: -0.400, -0.095; p = 0.002). The RCS results showed a steeper decline in blood Cd at ln-25(OH)D levels ≥ 3.19 (-0.272; 95% CI: -0.431, -0.112; p = 0.001). A significant negative interaction was identified between ln-25(OH)D and natural log-transformed dietary Ca intake on ln-Cd levels, suggesting that the inverse relationship between serum 25(OH)D and blood Cd levels grows stronger in the context of higher Ca intake, consistent with a statistical interaction rather than a simple additive effect (interaction β = -0.242; 95% CI: -0.462, -0.021; p = 0.032). CONCLUSION: In pregnant women in a nationally representative U.S. sample, higher 25(OH)D in the sera was linked to lower blood Cd. Importantly, we observed a statistical interaction between maternal vitamin D status and dietary calcium intake: the inverse association between 25(OH)D and blood cadmium appeared stronger at higher calcium intakes. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12884-025-08411-4.