Stopping the supply of iodized salt alone is not enough to make iodine nutrition suitable for children in higher water iodine areas: A cross-sectional study in northern China.

BACKGROUND: For the sake of children's health, iodized salt supply has been stopped in many areas with excessive iodine in the drinking water, but children's iodine nutrition status and thyroid function after terminating the iodized salt supply is unknown. Objective We assessed the iodine nutrition, thyroid function and influencing factors for thyroid abnormalities in children from areas with different concentrations of water iodine; the supply of iodized salt has been stopped in high water iodine areas. This study aimed to evaluate whether the strategy of stopping the supplies of iodized salt alone is enough to avoid thyroid dysfunction in all areas with excess water iodine while still meeting the iodine nutrition needs of children. METHODS: A cross-sectional study was conducted in children from four areas with different drinking water iodine concentrations in Tianjin, China. The drinking water samplings and spot urine samples were collected to estimate the external and internal iodine exposure levels. The thyroid volume was measured, and blood samples were collected to assess thyroid function. Logistic regression analysis was used to analyze risk factors for thyroid abnormalities. A dietary survey was conducted to determine the sources of iodine nutrition among the areas with different iodine concentrations in the drinking water. RESULTS: In the area with a drinking water iodine concentration ≥300 µg/L, the median urinary iodine concentration (UIC) in children was 476.30 (332.20-639.30) µg/L, which was higher than that in other groups (all P < 0.05), and the prevalence of thyroid nodules and the thyroid goiter rate were higher than those in the <100 µg/L, 100-150 µg/L and 150-300 µg/L areas (all P < 0.01). Binary logistic regression analysis indicated that the risk of thyroid abnormalities was significantly increased in the UIC 200-299 µg/L group (OR: 4.534; 95% CI: 1.565, 13.135; bootstrapped 95% CI: 1.689, 21.206, P = 0.004) and in the UIC ≥ 300 µg/L group (OR: 6.962; 95% CI: 2.490, 19.460; bootstrapped 95% CI: 2.838, 32.570, P = 0.001) compared to the 100-199 µg/L group. The iodine contribution rates from water in areas with water iodine concentrations ≥300 µg/L are up to 63.04%. CONCLUSIONS: After termination of the iodized salt supply, the level of iodine nutrition of children in the area with drinking water iodine concentrations ≥300 µg/L is still excessive. The water source needs to be replaced in this area. In the area with a water iodine concentration of 150-300 µg/L, it is proposed that stopping the supply of iodized salt is sufficient to achieve the proper iodine nutrition status in children.