Iodine Modifies the Susceptibility of Thyroid to Fluoride Exposure in School-age Children: a Cross-sectional Study in Yellow River Basin, Henan, China

Abstract

Excessive fluoride exposure has detrimental effects on the thyroid gland, which may be modified by iodine. However, the role of iodine in it remains unclear. This study aims to evaluate the role of iodine in thyroid abnormalities caused by fluoride exposure in school-age children. A total of 446 children aged 7–12 years were recruited from Tongxu County, Henan province, in 2017 (ZZUIRB 2017-018). We obtained demographic information through questionnaire surveys. The concentrations of urinary fluoride (UF) and urinary iodine (UI) were determined by the ion-selective electrode method and the catalytic spectrophotometric method, respectively. The radiation immunoassay was used to determine the serum concentrations of total triiodothyronine (TT3), total thyroxine (TT4), and thyroid-stimulating hormone (TSH). The B-mode ultrasound was performed to assess thyroid volumes (Tvols). The associations between fluoride exposure and thyroid-related indicators were tested by linear regression models. We found that Tvols increased by 0.22 (95% CI: 0.14, 0.31) cm3 with each standard deviation increment of UF. Moreover, Tvols in boys were more susceptible to fluoride exposure than those in girls, and the Tvols of children with high urinary iodine are less susceptible to fluoride exposure (P for interaction < 0.05). We also observed that TT3 levels were negatively related to UF concentrations at moderate urinary iodine levels (≤ 300 μg/l). Fluoride exposure can elevate the Tvols of school-age children, especially in boys, and high levels of iodine may alleviate this effect to some extent.

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Acknowledgments

We would like to express our deep thanks to all of the subjects enrolled in our study and their families. And we also want to give sincere thanks to all the staff for their efforts in this study.

Funding

This study was supported by the National Natural Science Foundation of China (81972981, 81673116), the Henan Department of Science and Technology, China (162300410272), and Zhengzhou University (2020zzuJXLX003).

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Correspondence to Yue Ba.

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Highlights

• The effects of fluoride on thyroid were evaluated in school-age children.

• Thyroid volumes have positive association with urinary fluoride in children.

• Iodine may modify the effects of fluoride on thyroid.

• Boys are susceptible to the damage of fluoride on thyroid.

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Du, Y., Zhou, G., Gong, B. et al. Iodine Modifies the Susceptibility of Thyroid to Fluoride Exposure in School-age Children: a Cross-sectional Study in Yellow River Basin, Henan, China. Biol Trace Elem Res (2021). https://doi.org/10.1007/s12011-020-02519-8

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Keywords

  • Fluoride
  • Iodine
  • Thyroid volumes
  • Thyroid-related hormones
  • Children