The study aimed to determine the adverse effects of iodine excess on children by examining the associations between thyroid volume (Tvol) and total goiter rate (TGR) with daily iodine intake.
In a multi-stage cross-sectional survey, we collected, on two nonconsecutive days, two 24-h urine samples and determined 24-h urinary iodine excretion and then calculated mean daily iodine intake assuming 92% iodine bioavailability. Ultrasonographic Tvol was measured for each participant to calculate TGR based on international and Chinese reference ranges for Tvol in children.
This study included 2089 children from two areas of Shandong province, where the median drinking water iodine concentration was 183 (69-406) µg/L. Median (IQR) 24-h urinary iodine concentrations for the two collections were 381(203-649) µg/L and 398 (202-687) µg/L, respectively. The mean daily iodine intake of children was 321 (164-536) µg/d. Tvols were slightly higher in boys (P=0.035). The TGR was 9.7%, and did not differ between boys and girls. Tvols became higher as iodine intake increased, and TGR increased with increased iodine intake (?2=107.067, P<0.001). TGR exceeded 5% when daily iodine intake was 200-250µg/d. Using logistic regression and two-piecewise linear regression, a nonlinear association was observed between Tvols, TGR and iodine intake levels, with a threshold at an iodine intake level of 110µg/d.
Thyroid volume and the risk of TGR began to increase in children when daily iodine intake is >110 µg/d, and the TGR exceeded 5% with iodine intake >200 µg/d-250 µg/d. 110-250µg/d appears to be an optimal iodine intake range for school-age children.