As VD regulates genes expression Se is the main structure of selenoproteins affecting thyroid function as glutathione peroxidase (GPXs), thioredoxin reductases (TRs), and iodothyronine deiodinases (DIO). As a part of the antioxidant defence system, those enzymes protect the thyroid from oxidative stress because of hydrogen peroxide generated naturally from iodide oxidation during the production of thyroid hormones. Se is also an essential trace element for the synthesis of T3, rT3 and T2 by being a part of DIO (Iodothyronine deiodinases). As a result of Se deficiency increased T4 43, fT4 (free thyroxinefT4) and reduced T3 level are observed. The thyroid gland contains the highest amount of Se per gram in the whole human body. Its deficiency directly impacts thyroid metabolism and immune function and leads to radical and autoimmune destruction of the gland and formation of fibrotic tissue.
Despite the fact that Se sources are widely eaten there is still seen inadequate daily intake in Europe (about 40 µg per day) and other parts of the world. Scientific Committee on Food of the European Commission recommends a daily intake of 55 µg of Se daily
Selenium and Iodine
A meta-analysis by O'Kane et al. based on observational and the interventional studies concluded that the status of Se is positively associated with iodine status. Iodine is an important compound for expression and function of proteins and enzymes necessary for the metabolism of thyroid hormones and biosynthesis. Besides iron and zinc, Se deficiency can diminish iodine metabolism and effectiveness of iodine supplementation in HT(Hashimoto’s disease) deficient patients. Iodine deficiency needs to be corrected concomitantly with Se deficiency. There is an importance of keeping iodine level within normal range as accordingly to U shape disease risk, deficiency and excess of iodine might exacerbate thyroid dysfunction and develop iodine-induced hypothyroidism. As mentioned before, Mg is necessary for iodine uptake by thyroid and replenishment of it might increase iodine bioavailability for the gland
What foods provide selenium?
Selenium is found naturally in many foods. The amount of selenium in plant foods depends on the amount of selenium in the soil where they were grown. The amount of selenium in animal products depends on the selenium content of the foods that the animals ate. You can get recommended amounts of selenium by eating a variety of foods, including the following:
- Seafood
- Meat, poultry, eggs, and dairy products
- Breads, cereals, and other grain products
Suplementation
It is worth to note that non-rare Se deficiency seen in HT patients’ needs to be replenished in a caution of potentially toxic effects of plasma Se excess level >140 µg/L. Because some adverse health effects were observed in studies using generally accepted as sage 200 µg of Se daily (alopecia, dermatitis, squamous cell carcinoma, type II diabetes) in non-deficient Se patients the therapeutic dose should be addressed individually. Se supplementation should be discarded if plasma Se level is adequate (~125 µg/L) as there is a U-shaped relationship between Se concentration and disease risk. In an RCT(Randomized controlled trial) of UK elderly patients, a dose of 100 µg/d increased plasma Se concentration from 91.3 µg/L to ~140 µg/L which is well enough for selenoproteins synthesis 58. We believe that the dosage of 200 µg/d of Se in deficient patients is safe. Although, it is prudent to check Se status before initiating any the treatment with it uses.
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Kawai, M., Shoji, Y., Onuma, S., Etani, Y. and Ida, S, “Thyroid hormone status in patients with severe selenium deficiency”, Clin Pediatr Endocrinol, 27 (2). 67-74. 2018.
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Gashu, D., Marquis, G.S., Bougma, K. and Stoecker, B.J, “Selenium inadequacy hampers thyroid response of young children after iodine repletion”, J Trace Elem Med Biol, 50. 291-5. 2018.
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| Rayman, M.P. and Duntas, L.H, “Selenium Deficiency and Thyroid Disease”. In: Luster, M., Duntas, L. and Wartofsky, L. (editors), The Thyroid and Its Diseases: A Comprehensive Guide for the Clinician, Springer, 2019, 109-126. http://pubs.sciepub.com/jfnr/7/8/6/index.html https://ods.od.nih.gov/factsheets/Selenium-Consumer/#h3 |
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