Objective To investigate the changes in iodine nutritional status among school-aged children in water-borne high-iodine areas of Xuzhou, China following comprehensive water source conversion for iodine reduction.

Methods According to the Jiangsu Province Surveillance Protocol for Water-Borne High-Iodine Areas, 34-35 water-borne high-iodine villages in Xuzhou were selected annually from 2022 to 2025 using systematic sampling as surveillance sites. The iodine content of residential drinking water, as well as salt iodine, urinary iodine, and thyroid volume measurements among children aged 6-12 years were monitored.

Results From 2022 to 2025, a total of 138 water samples were tested, with water iodine concentrations ranging from 13.5 to 60.8 μg/L and a median (P₂₅, P₇₅) of 32.2 (25.8, 41.9) μg/L. A total of 5 284 salt samples were examined, revealing a non-iodized salt consumption rate of 95.72%. Analysis of 5 284 urine samples from children yielded a median urinary iodine concentration (P₂₅, P₇₅) of 340.83 (216.13, 509.75) μg/L; the annual medians were 403.91, 305.62, 350.53, and 313.56 μg/L from 2022 to 2025, respectively, showing a fluctuating downward trend and consistently remaining at levels indicative of iodine excess. Thyroid volume was measured in all 5 284 children, with the goiter rate remaining below 5% each year. A positive correlation was observed between urinary iodine concentration and water iodine content (r_s=0.187, P < 0.001).

Conclusion From 2022 to 2025, urinary iodine levels among children in water-borne high-iodine areas of Xuzhou decreased substantially, yet remained at an iodine excess level. Future efforts should prioritize non-water iodine intake pathways in children and implement relevant prevention and control measures to further optimize targeted prevention and control strategies.