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

Abstract

Background: Excessive iodine intake may have adverse effects on the thyroid, particularly in children, but the safe upper iodine intake concentration in children is unclear.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 μg/L (69–406 μg/L). The median (IQR) 24-h urinary iodine concentrations for the 2 collections were 381 μg/L (203–649 μg/L) and 398 μg/L (202–687 μg/L), respectively. The median (IQR) habitual daily iodine intake of children was 298 μg/d (186–437 μg/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 ∼5% for children aged 7–10 and 11–14 y at iodine intakes of 200–249 and 250–299 μg/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 μg/d.Conclusions: Tvol begins to increase in children when iodine intake is ≥150 μg/d, and the TGR exceeds 5% when daily iodine intake is ≥250 μg/d for children aged 7–10 y and ≥300 μg/d for children aged 11–14 y. Our findings suggest that 150–249 and 150–299 μg/d seem to be safe upper iodine intake ranges for children aged 7–10 and 11–14 y, respectively. This trial was registered at clinicaltrials.gov as NCT02915536.