In this article, we are going to talk about the connection between Selenium and the Thyroid GlandSelenium is an essential micronutrient with many effects on the organism. For example, it has antioxidant and anti-inflammatory properties. But today, we are interested in its role in the synthesis of thyroid
In fact, the thyroid gland is the organ with the highest Selenium content per gram of tissues. It has at least 30 of the so called Selenoproteins, enzymes like glutathione peroxidase (GPX), thioredoxin reductase (TR), iodotyrosine deiodinase or selenoprotein P.
Selenium and the Thyroid Gland
Selenium supplementation in patients who suffer autoimmune hypothyroidism seems to change the inflammatory and immune response. Particularly, it probably increases the glutathione peroxidase and thioredoxin reductase levels while reducing the H2O2 concentrations (hydrogen peroxide). Consequently, this results in the creation of thyroid hormones.
The creation of thyroid hormones produces oxidative stress, although said proteins buffer this effect
When we have enough Selenium, the GPX and TR protect the thyrocyte (thyroid cell) against the harmful effects of these peroxides. Moreover, there is evidence that the deiodinase D1 and D2 improve the conversion of T4 to T3 (a biologically active hormone). They are selenoproteins and, therefore, a Selenium deficiency would hinder the conversion of T4 to T3 (1).
This is key because a higher biological activity of the thyroid hormones affects the T3 after binding to the nuclear receptor.
Foods Rich in Selenium
Selenium is a mineral that is found in the soil and we obtain it from the plants that absorb it through their roots
Therefore, the Selenium content of animals and plants alike will vary if the ground is seleniferous or not. The recommended daily amount of Selenium would be 55-75mcg in order to stimulate the GPX activity.
For example: Brazil nuts, oysters, tuna, whole wheat, sunflower seeds, beef, pork, lamb, turkey, chicken and mushrooms.
As you can see, an omnivore and varied diet should not be selenium deficient
How much Selenium do we take?
Some studies have assessed the usual Selenium intake in the West. For instance, Greeks take an average of 39.9 mcg of selenium a day per person. Although this is actually quite lower than the minimum recommended daily dose (2).
Following the same research, Wichman conducted a meta-analysis in 2016. In it, we can observe how the TPO levels dropped after three, six and twelve months in patients who took LT4 but not in the ones who did not (5).
Regarding epidemiological studies, this Chinese study (6) assessed how thyroid disease was more prevalent in regions with low Selenium intake (Se <69 mcg) when compared to regions with a proper intake (>69 mcg).
Side effects of Selenium
However, we need to be cautious since high doses of Selenium can be toxic for humans
For example, taking 330mcg daily could be toxic for the hormone production, such as GH, IGF-1 or thyroid hormones. Although it would not cause Selenosis, which could otherwise happen with higher doses.
These are some of its side effects: hair loss, anorexia, diarrhea, depression, hemorrhages, hepatic and renal necrosis, blindness and even ataxia (6)
In addition, a selenium deficiency speeds up the depletion of Iodine in the thyroid gland. Above all, this could be a protective adaptation when there is not enough Selenium and plenty of Iodine.
That is why, taking Selenium deteriorates the thyroid gland in Zaire, a region with endemic goiter.
In fact, this suggests that in iodine-deficient areas, the body reduces the conversion of T4 or T3 in order to save Iodine. Moreover, using Selenium supplementation would only accelerate this loss of iodine in order to increase said conversion (7).
First of all, to see if selenium supplementation would be useful for a patient, we need to assess the urinary excretion of Iodine in 24h. However, this can be conditioned by the intake of food rich in iodine or other factors.
- Maia, A. L., Goemann, I. M., Souza Meyer, E. L., & Wajner, S. M. (2011). Type 1 iodothyronine deiodinase in human physiology and disease. Journal of Endocrinology, 209(3), 283-297.
- Pappa, E. C., Pappas, A. C., & Surai, P. F. (2006). Selenium content in selected foods from the Greek market and estimation of the daily intake. Science of the Total Environment, 372(1), 100-108.
- Toulis, K. A., Anastasilakis, A. D., Tzellos, T. G., Goulis, D. G., & Kouvelas, D. (2010). Selenium supplementation in the treatment of Hashimoto’s thyroiditis: a systematic review and a meta-analysis. Thyroid, 20(10), 1163-1173.
- Fan, Y., Xu, S., Zhang, H., Cao, W., Wang, K., Chen, G., … & Liu, C. (2014). Selenium supplementation for autoimmune thyroiditis: a systematic review and meta-analysis. International journal of endocrinology, 2014.
- Wichman, J., Winther, K. H., Bonnema, S. J., & Hegedüs, L. (2016). Selenium supplementation significantly reduces thyroid autoantibody levels in patients with chronic autoimmune thyroiditis: a systematic review and meta-analysis. Thyroid, 26(12), 1681-1692.
- Wu, Q., Rayman, M. P., Lv, H., Schomburg, L., Cui, B., Gao, C., … & Li, H. (2015). Low population selenium status is associated with increased prevalence of thyroid disease. The Journal of Clinical Endocrinology & Metabolism, 100(11), 4037-4047.
- Fan, A. M., & Kizer, K. W. (1990). Selenium. Nutritional, toxicologic, and clinical aspects. Western Journal of Medicine, 153(2), 160.
- Contempre, B., Duale, N. L., Dumont, J. E., Ngo, B., Diplock, A. T., & Vanderpas, J. (1992). Effect of selenium supplementation on thyroid hormone metabolism in an iodine and selenium deficient population. Clinical endocrinology, 36(6), 579-583.
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