Selenium and thyroid hormone - Selenium for hypothyroidism

Selenium is essential for proper functioning of our immune system and thyroid gland.

Selenium is an essential trace mineral required for the human body in small amounts for boosting immunity against diseases as well as protecting it from oxidative free radicals.
Its deficiency has direct effect on the thyroid gland which are regulators of body's metabolism, growth and function.
The proper utilization of hormones, thyroxine (T4 or C15H11I4NO4) and triiodothyronine (T3 or C15H12I3NO4) and the conversion of T4 to active T3 is mediated and influenced by the quantities of selenium available in the body.

Selenium and thyroid function

For the proper hormone synthesis in the gland and its activation and metabolism, essential trace minerals iodine and selenium are required.
In the human body selenium concentration is highest in the thyroid gland among all organs.
Thyrocytes (gland epithelial cells, follicular cells and acinar cells) secrete the hormones thyroxine (T4) and triiodothyronine (T3).
In their biochemical activities thyrocytes produce H2O2 continuously for oxidative hormone synthesis.
Many selenium containing selenoenzymes are functionally expressed in thyrocytes as glutathione peroxidases, thioredoxin reductases, type I 5-deiodinase, type II 5-deiodinase and selenoprotein P.
Selenoenzymes form an effective cell defence mechanism against hydrogen peroxide and other reactive oxygen species, protecting the gland and maintaining its normal function.

Selenium for thyroid problems and autoimmune inflammation

Autoimmune diseases are disorders of the gland wherein the body's own immune system attacks the gland cells.
The incidence of the thyroid inflammation is higher in regions with selenium deficiency.
It is found that deficiency of selenium, even at mild levels, can contribute to initiation of the gland disorders including autoimmune diseases.
It is also found that continued use of supplements has a positive effect on the these autoimmune diseases, alleviating many of the symptoms.
In a study by Roland Gärtner, Barbara C. H. Gasnier, Johannes W. Dietrich, Bjarne Krebs and Matthias W. A. Angstwurm of University of Munich, Germany, it was found that Selenoenzymes have diverse effects on the immune system and also within the this gland.
GPx antioxidant activity is markedly diminished during severe selenium deficiency.
This reduced antioxidant activity may initiate and contribute to oxidative damage of cells of this gland and fibrosis.
In such conditions thyroid peroxidase antibodies (TPOAb) may be formed leading to autoimmune thyroiditis.
Leonidas H. Duntas, University of Athens, Greece, in a recent paper 'Selenium and the Thyroid: A Close-Knit Connection' which is published by Journal of Clinical Endocrinology & Metabolism concluded that ' Maintenance of "selenostasis" via optimal intake not only aids preservation of general health but also contributes substantially to the prevention of the gland disease'.
It is believed that viral and genetic components and gender could be co-factors triggering diseases like Grave’s Disease and Hashimoto's Thyroiditis in the absence of selenium antioxidant protection.

Effect of selenium on the thyroid hormones T4 and T3

Our understanding of the function of the mineral in metabolism has undergone major advancement with early 2000 discoveries.
Selenoenzymes control or modulate many functional aspects of the metabolism of T4 and T3 hormones. Selenium-enzymes bring about the process of iodination of thyroglobulin in the gland.
In humans type I iodothyronine deiodinase is the enzyme responsible for most of the peripheral conversion of thyroxine or 3,5,3',5'-tetraiodothyronine (T4) to the active form 3,3',5-triiodothyronine (T3).
Type I iodothyronine deiodinase has been found to be a selenoenzyme.
Type II deiodinase is responsible for T4 conversion to T3 in the brain.
Type III deiodinase is the inner ring deiodinase responsible for deactivating T4 and T3.
It was recently found that both type I and type II are also selenocysteine enzymes containing selenium.
In a study conducted by Wayne Chris Hawkes and Nancy L. Keim of University of California, it was found that the serum level of T3 increased with low Selenium diet at 14 mcg/day leading to weight loss and sub clinical hyperthyroid responses.
However it also found that high Selenium diet of 297 mcg/day led to weight gain and sub clinical hypothyroid responses with decrease in serum T3.
Thus it is clearly evident that this mineral has direct effect on the hormone leading to hyperthyroid response or hypothyroid response depending on the deficiency or excess of its presence.
It is imperative to maintain optimum selenium status through foods and if necessary by supplementation for general health of the body and thyroid gland in particular.
Related topics on role of the essential trace mineral selenium in human body:
Food sources
Antioxidant functions
For prostate cancer
Treatment of Keshan disease
SELECT for cancer prevention
For heart disease
HIV/AIDS treatment
Selenium overdose and side effects
Supplements and dosage
Selenium and thyroid hormone - Selenium for hypothyroidism (current topic)

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