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

Am J Clin Nutr. 2017 Jan;105(1):228-233. doi: 10.3945/ajcn.116.139725. Epub 2016 Dec 7.

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.

Keywords: children; thyroid volume; total goiter rate; urine iodine concentration; urine iodine excretion.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Child
  • China / epidemiology
  • Cross-Sectional Studies
  • Drinking Water / chemistry*
  • Female
  • Goiter / epidemiology
  • Goiter / etiology*
  • Humans
  • Iodine / administration & dosage
  • Iodine / adverse effects*
  • Iodine / urine
  • Male
  • Prevalence
  • Reference Values
  • Thyroid Gland / drug effects*
  • Trace Elements / administration & dosage
  • Trace Elements / adverse effects*
  • Trace Elements / urine

Substances

  • Drinking Water
  • Trace Elements
  • Iodine

Associated data

  • ClinicalTrials.gov/NCT02915536