Selenium is Vital to Thyroid Function

Selenium is Vital to Thyroid Function
Selenium is highly concentrated in the thyroid gland, more so than in any other organ in the human body, indicating its vital need in normal thyroid function. It acts as an antioxidant that protects the thyroid gland, a cofactor nutrient that facilitates the production of thyroid hormone, and as a nutrient that is required to facilitate the conversion of T4 to T3 (triiodothyronine, active thyroid hormone that works inside cells to set the pace of metabolism).

Selenium combines with the sulfur-containing amino acid cysteine to make a special protein known as selenocysteine, a selenoprotein. There are 30 selenoproteins that are currently identified, mostly involving the antioxidant defense system and thyroid function.

The selenium-containing antioxidant enzymes are known as glutathione peroxidases (GSH). Six different GSH enzymes have now been identified; helping to protect the inside of cells, the GI tract, the reproductive system, and operating in fluids between cells. GSH enzymes are vital to maintaining normal health. They are now proven to protect the thyroid gland during thyroid hormone formation.

The formation of thyroid hormone occurs on cell membranes of thyroid cells known as thyrocytes. This process requires selenium as a cofactor nutrient. During this process the enzyme thyroid peroxidase (TPO) prepares iodine for attachment to tyrosine to form thyroid hormone. The normal activity of TPO generates tremendous numbers of free radicals within the thyroid gland in the form of H2O2 and lipid peroxides. These must be deactivated by GSH enzymes, otherwise the production of thyroid hormone stresses and inflames the thyroid gland. This can easily result in a reduced rate of thyroid hormone formation. Its like trying to run on a sprained ankle, except it is a sprained thyroid.

Selenoproteins also act in various ways to change T4 into T3 (active thyroid hormone) and reverseT3 (which inactivates T3). Three main selenoproteins activate and inactivate thyroid hormone, known as D1, D2, and D3.

D1 is the primary activator of thyroid hormone for your body, working mostly in the liver and to some degree in the kidneys. D2 is active in the thyroid gland, brain, nerves, and heart. It plays the primary role in thyroid activation in the brain under normal conditions, and produces thyroid hormone for the rest of the body under stressed conditions. D3 is mostly a brake on thyroid hormone activity, turning off active hormone.

When your body starts to run low on selenium the activation of thyroid hormone by D1 may drop by 90%. Your body compensates by turning on the back up system, using the D2 enzyme to maintain active thyroid hormone. The problem with this back up system running for any great length of time is that is causes significantly increased production of free radicals. Even worse, the lack of selenium already handicapped the primary antioxidant that protects the thyroid gland and liver, GSH. Thus, selenium deficiency forces the body into a very uncomfortable metabolic coping strategy that eventually leads to slower metabolism, increased oxidative stress, and wear and tear to the thyroid gland and liver.*

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