Thyroid hormone synthesis occurs in 5 main steps

Step 1: The follicular cells in the thyroid gland contain thyrocytes that produce the tyrosine rich compound thyroglobulin which is a precursor to the thyroid hormones. Thyroglobulin is stored within the lumen of the follicular cells.

Step 2: PAK phosphorylation stimulates the activity of specialised NA+-K+-ATPase pumps on sodium-iodidesymporters (NIS) in the cell wall which transport inorganic iodine into the thyrocytes. NIS activity is sensitive to both TSH stimulation and iodide availability. This step is the controlling factor for making iodide available for thyroid hormone synthesis.

Step 3: PAK phosphorylation also stimulates the iron-containing enzyme thyroid peroxidase (TPO) which carries out three main actions that occur in the thyroid colloid and on the inner membrane of the follicular cells – oxidation, organification, and coupling reaction:

• • Oxidation requires hydrogen peroxide and iodine. TPO converts (oxidises) iodide (I—) to iodine (I2/ Molecular iodine, sometimes referred to as IO) via the influence of hydrogen to hydrogen peroxide and the resulting reactive oxygen species generated during this process.
  • Organficiation: TPO connects I2/IO with tyrosine residues in thyroglobulin. This produces monoiodotyrosine/T1 (MIT – tyrosine residue + iodine) and diiodotyrosine/T2 (DIT – tyrosine residue + 2 iodine molecules).
  • Coupling reaction: TPO links MIT with DIT to form Triiodothyronine (T3) and two DIT molecules to form Tetraiodothyronine/Thyroxine (T4

Step 4: Thyroid hormones are bound to thyroglobulin and stored until needed.

Step 5: Thyroid hormones are released by the cleavage of MIT/ T1, DIT/T2, T3, and T4 from thyroglobulin. T3 and T4 are then released into the blood while MIT and DIT are broken down, and the resulting free iodine enters the intracellular iodine pool for recycling. Once released, thyroid hormone can travel to and interact with almost every cell in the body on transporter proteins including thyroxine-binding globulin (TBG) which carries around 66% of thyroid hormone, transthyretin and albumin. Once the thyroid hormones reach their target site, they leave their transport molecule and move into the cell by either diffusion or by a carrier. Hormone binding activates the production of transcription factors leading to gene activation and cellular changes. The conversion of T4 to T3 (deiodination) occurs under the influence of a group of selenoproteins called deiodinase (DIO) enzymes and thus is selenium-dependent.

Iodine

The necessity for iodine in thyroid hormone synthesis is essential. The thyroid gland usually contains 20-50 times more free iodide than the plasma (and much more in cases of hyperthyroidism). As explained above, iodine is an intrinsic component of the thyroid hormones themselves. 65% of the weight of T4 and 58% of the weight of T3 is iodine, therefore iodine is critical for the adequate synthesis of the thyroid hormones.

Selenium

Selenium, a potent antioxidant and component of the indispensable biological enzyme glutathione peroxidase, is present throughout the process of thyroid hormone synthesis. The thyroid gland contains one of the highest concentrations of selenium per gram than any other tissue in the body.5 Thyroid hormone production cannot take place in the absence of oxidation reactions involving hydrogen peroxide. Life-long exposure to and assault from to this highly reactive molecule is cushioned by the constant presence of selenium in the colloid and follicular tissues. Further to this, as a component nutrient to the deiodinase enzymes, selenium plays a major role in the conversion of T4 to T3. The selenium utilised in Designs for Health’s Thyroid Synergy is from a selenium-enriched yeast ingredient known as SelenoExcell®, a specialised and highly bioavailable form of selenium that is organically bound to non-GMO Saccharomyces cerevisiae via a fermentation process. During this process, selenium is incorporated into the cell wall of Saccharomyces cerevisiae, replacing sulphur. Up to 21 selenium compounds are created during this process, including selenomethionine, selenocysteine and methyl-selenocysteine – compounds found commonly in foods as bioavailable sources of selenium.

Tyrosine

Tyrosine is a component part of thyroglobulin – the compound stored in the thyroid colloid that serves as a precursor to the thyroid hormones (the thyroid hormones are iodinated molecules of tyrosine).

Directions to use:

Allergen Information:

• No added: Gluten, Dairy, Nuts, Seeds, Egg, Soy.
• Free From: Artificial colours, Artificial flavours, Sulfites, Benzoates, Sorbates.
• Vegan Friendly

Warnings:

• Dietary supplements should not replace a balanced diet.
• This medicine contains selenium, which is toxic in high doses. A daily dose of 150 micrograms for adults of selenium from dietary supplements should not be exceeded.

• Doses of selenium above 400 micrograms daily over the long term can increase the risk of developing selenium toxicity.
• Doses of iodine above 1100 micrograms daily over the long term may increase the risk of or exacerbate thyroid dysfunction, thyroiditis and thyrotoxicosis.