Associations between iodine intake, thyroid volume, and goiter rate in school-aged Chinese children from areas with high iodine drinking water concentrations

Objective: We assessed the adverse effects of high iodine intake from iodine-rich drinking water on thyroid size in children by examining associations between thyroid volume (Tvol), total goiter rate (TGR), and iodine intake. Design: In a multistage cross-sectional survey, we collected two 24-h urine samples on 2 nonconsecutive days and determined 24-h urinary iodine excretion, then calculated habitual daily iodine intake. Ultrasonographic Tvol was measured, and TGR was calculated based on international and Chinese reference ranges for Tvol in children. Results: This study included 2089 children from Shandong province, where the median (IQR) drinking water iodine concentration was 183 mu g/L (69406 mu g/L). The median (IQR) 24-h urinary iodine concentrations for the 2 collections were 381 mu g/L (203649 mu g/L) and 398 mu g/L (202687 mu g/L), respectively. The median (IQR) habitual daily iodine intake of children was 298 mu g/d (186437 mu g/d). Tvols were slightly higher in boys than in girls (P = 0.035). The overall TGR was 9.7% and did not differ by sex. The TGR was similar to 5% for children aged 710 and 1114 y at iodine intakes of 200249 and 250299 mu g/d, respectively. With the use of logistic regression and 2-step linear regression, a nonlinear association was observed between Tvol, TGR, and iodine intake, with a threshold intake of 150 mu g/d. Conclusions: Tvol begins to increase in children when iodine intake is =150 mu g/d, and the TGR exceeds 5% when daily iodine intake is =250 mu g/d for children aged 710 y and >= 300 mu g/d for children aged 1114 y. Our findings suggest that 150249 and 150299 mu g/d seem to be safe upper iodine intake ranges for children aged 710 and 1114 y, respectively.