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Synthesis and Regulation of Thyroid Hormones

Synthesis and Regulation of Thyroid Hormones

Low blood levels of the thyroid hormones — triiodothyronine (T3) and thyroxine (T4) — signal the hypothalamus to release the thyrotropin-releasing hormone (TRH). TRH then reaches the pituitary gland and stimulates the release of thyroid-stimulating hormone(TSH) into the bloodstream.
Upon reaching the thyroid gland, TSH stimulates the follicular cells' active uptake of iodide ions from the blood. The ions diffuse to the apical surface of the cells and are oxidized to iodine. The iodine is then...

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Hyperthyroidism is a hypermetabolic state caused by elevated levels of thyroid hormones, triiodothyronine (T3) and thyroxine (T4). It results from dysregulation at the thyroid, pituitary, or immune system level and affects multiple organ systems.PathophysiologyThe most common cause of hyperthyroidism is Graves’ disease, an autoimmune disorder in which antibodies, specifically thyroid-stimulating antibodies (TSAb), a subtype of TSH receptor antibodies (TRAb), bind to and activate TSH receptors...

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Related Experiment Video

Updated: May 26, 2026

A Microplate Assay to Assess Chemical Effects on RBL-2H3 Mast Cell Degranulation: Effects of Triclosan without Use of an Organic Solvent

A Microplate Assay to Assess Chemical Effects on RBL-2H3 Mast Cell Degranulation: Effects of Triclosan without Use of an Organic Solvent

Published on: November 1, 2013

Long term use of triclosan toothpaste and thyroid function.

Mary P Cullinan¹, Janet E Palmer, Anne D Carle

¹Sir John Walsh Research Institute, University of Otago, Dunedin, New Zealand. mary.cullinan@otago.ac.nz

The Science of the Total Environment

|December 27, 2011

Summary

This 4-year study found that triclosan toothpaste did not affect thyroid function. Thyroid stimulating hormone (TSH), free thyroxine (fT4), and free triiodothyronine (fT3) levels remained stable in the triclosan group, indicating safety.

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Last Updated: May 26, 2026

A Microplate Assay to Assess Chemical Effects on RBL-2H3 Mast Cell Degranulation: Effects of Triclosan without Use of an Organic Solvent

A Microplate Assay to Assess Chemical Effects on RBL-2H3 Mast Cell Degranulation: Effects of Triclosan without Use of an Organic Solvent

Published on: November 1, 2013

In vivo Characterization of Endocrine Disrupting Chemical Effects via Thyroid Hormone Action Indicator Mouse

In vivo Characterization of Endocrine Disrupting Chemical Effects via Thyroid Hormone Action Indicator Mouse

Published on: October 6, 2023

Area of Science:

Endocrinology
Toxicology
Public Health

Background:

Triclosan, an antimicrobial agent in toothpaste, shares structural similarities with thyroid hormones.
Animal studies suggest potential reductions in serum thyroid hormone levels following triclosan exposure.
The long-term effects of triclosan-containing toothpaste on human thyroid function remain largely unknown.

Purpose of the Study:

To assess the long-term effects of 0.3% triclosan toothpaste on thyroid function over a 4-year period.
To compare thyroid function markers between individuals using triclosan toothpaste and those using a placebo.
To evaluate the safety of triclosan toothpaste concerning thyroid health in subjects with coronary heart disease.

Main Methods:

A randomized, placebo-controlled clinical trial involving 132 subjects with coronary heart disease.
Participants were assigned to use either 0.3% triclosan toothpaste or a placebo toothpaste.
Thyroid stimulating hormone (TSH), free thyroxine (fT4), free triiodothyronine (fT3), antithyroglobulin antibody (anti-TGab), and antithyroid peroxidase antibody (TPOab) were measured at year 1 and year 5.

Main Results:

No significant differences in TSH, fT3, or antithyroid antibodies were observed between the triclosan and placebo groups at year 1 or year 5.
At year 5, a significant difference in fT4 levels was noted, with reduced levels in the placebo group but not in the triclosan group (p=0.01).
The triclosan group showed stable fT4 levels throughout the 4-year study period.

Conclusions:

Four years of using 0.3% triclosan toothpaste demonstrated no detectable adverse effects on overall thyroid function.
The findings support the safety of triclosan-containing toothpaste, with no significant thyroid-related adverse effects observed.
The study provides evidence for the safe use of triclosan in toothpaste for thyroid health.