Fig. 7. Schematic representation of the mechanism of how iodine intake altered the composition of gut microbiota and metabolites to accelerate the progress of HT.

Thyroid-gut axis plays an important role in the development of HT, indicating that the intestinal microbiota and its metabolites may act directly or indirectly on the thyroid by influencing intestinal microelement uptake and immune regulation. Excess iodine intake increases intestinal permeability, and leads to gut dysbiosis, disrupting TH17/Treg balance by reducing butyric acid. The blue downward arrows indicate downregulation/decrease. The red upward arrows indicate upregulation/increase. Abbreviation: HT, Hashimoto thyroiditis; LPS: Lipopolysaccharide; TgAb: thyroglobulin antibody.