Blood lead levels and associated factors among preschool children in Ningbo, China: a cross-sectional study

Objective This cross-sectional study aimed to investigate blood lead levels (BLLs) and their associated factors among preschool children (aged 3–7 years) in Ningbo, China. The findings may inform hypotheses for future prevention strategies against childhood lead exposure. Methods Stratified Cluster sampling method was used to select three kindergartens in Ningbo, China, as study sites between January and May 2026. Questionnaire investigation about family, life, and behavioral conditions, venous blood samples collection and BLL detection are conducted. Results In this study, an elevated BLL was defined as ≥35 μg/L. Of 595 children, 44 (7.39%) had elevated BLLs (≥35 μg/L; mean 19.43 μg/L). Before adjustment, lower 25-hydroxyvitamin D, town residence, factory proximity, coal gas use, and higher beverage frequency were associated with elevated BLLs ( p < 0.001, p = 0.019, p = 0.022, p = 0.040, p < 0.001, respectively). After the adjustment, multivariable analysis showed each 1 μg/L increase in 25-hydroxyvitamin D (25(OH)D) was associated with 5% lower odds of elevated BLL (adjusted OR = 0.95, 95% CI: 0.90–0.99). Subgroup analyses revealed there is a significant interaction in males (OR = 0.92, 95% CI: 0.88–0.97) and town residents (OR = 0.92, 95% CI: 0.87–0.97). Conclusion The level of 25(OH)D was significantly negatively correlated with the blood lead concentration (OR = 0.95, 95% CI: 0.90–0.99, p = 0.012). The level of 25(OH)D in the group with elevated blood lead was 19.5% lower than that in the normal group. The frequency of consuming sugary beverages was positively correlated with elevated blood lead levels (2–3 times per month: OR = 2.91; 2–3 times per week: OR = 4.72, p = 0.002). Living within 1,000 m of a factory, using liquefied gas, and living in a town were also associated with elevated blood lead levels. Subgroup analysis showed that this negative correlation was more significant in males ( p = 0.001) and city children ( p = 0.005). These cross-sectional associations suggest that 25(OH)D status and sugary beverage intake are correlated with BLLs in preschool children; however, causality cannot be inferred, and longitudinal or intervention studies are needed to clarify the direction of these relationships.