Autoimmune thyroiditis is the umbrella term for various types of thyroiditis in which the immune system mistakenly attacks the thyroid gland.
The result is often hypothyroidism, the insufficient functioning of the thyroid gland.
The two major types of hypothyroidism are Hashimoto’s disease and atrophic thyroiditis.
Thyroiditis is the medical term for inflammation of the thyroid gland.
Immune system disorder can also cause an overactive thyroid, called hyperthyroidism; Graves’ disease is the most common form.
Selenium Supplementation to Prevent Hypothyroidism
In a 2021 review article, Filipowicz et al assert that many European endocrinologists prescribe selenium supplements to autoimmune thyroiditis patients.
For example, a 2016 survey of 815 doctors (91% endocrinologists) has shown that almost 80% of the surveyed doctors prescribe selenium supplementation to autoimmune thyroiditis patients. The rationale for the selenium supplementation is the delay of the hypothyroidism or a decrease in thyroid antibodies [Filipowicz 2021].
40% of the surveyed doctors prescribe selenium supplementation for autoimmune thyroiditis women who are pregnant or conceiving. The rationale in the case of the pregnant women patients is the prevention of
postpartum thyroiditis [Filipowicz 2021].
The preferred dosage in all groups is 100–200 mcg/day [Filipowicz 2021].
Filipowicz et al [2021] recommend organic selenium supplements rather than inorganic forms. They especially recommend a patented Danish product SelenoPrecise®, which contains organic selenium yeasts with100 mcg of selenium per tablet with 66% of the selenium content as selenomethionine plus more than 20 other organic selenium compounds and with less than 1% of inorganic selenium forms). There is a with a high bioavailability of 88.7% [Bügel 2008].
The European Food Safety Authority (EFSA) has tested this product and concluded that the product is sufficiently well characterized with respect to the selenium content and the nature of the selenium compounds contained in it. Moreover, the EFSA has concluded that the use of selenium-enriched yeast as a source of selenium when used in foods (including food supplements) for the general population does not present a safety concern at the proposed intake levels [EFSA 2008].
Low Dietary Selenium Intakes in Europe
In Europe, selenium supplementation is often necessary because dietary selenium intakes in much of Europe are too low for the citizens of European countries to achieve an optimal plasma/serum selenium concentration of 120–125 mcg/L, which is the concentration associated with maximal selenoprotein activity and sufficient selenium storage [Filipowicz 2021].
U-Shaped Relationship Between Selenium Status and Health Effects
According to Professor Margaret P. Rayman, University of Surrey, UK, only individuals with low selenium status are candidates for selenium supplementation. Prof. Rayman’s U-shaped graph shows that the disease risk will be high when the selenium status is low and then the recommendation will be to increase dietary selenium intake. However, the disease risk will be low whenever the selenium status is optimal (at serum/plasma concentrations of 125 mcg/L), and then the recommendation will be not to supplement [Winther 2020, figure 3].
With respect to a possible relationship between selenium status and the risk of developing type-2 diabetes, Winther et al [2020] make the following points:
- Evidence from observational studies (which cannot show a cause-effect relationship) seem to show an association between higher blood selenium levels and type-2 diabetes whereas evidence from randomized controlled trials shows that there is not a greater risk of developing type-2 diabetes in individuals taking selenium supplements than there is in individuals taking placebo supplements.
- It is not clear why the evidence from observational studies and from intervention studies differs.
Professor Lutz Schomburg, Berlin, Germany, has suggested that the diabetes and insulin resistance lead to increased synthesis of selenoprotein P, the primary transporter of selenium in the blood, thus explaining the association between high blood selenium levels and the incidence of type-2 diabetes. In this theory, higher selenium status does not increase diabetes risk, but, rather, diabetes causes increasing selenoprotein P synthesis and higher selenium concentrations in the blood [Schomburg 2020].
In normal non-diabetic conditions, insulin decreases selenoprotein P biosynthesis and secretion; in conditions of insulin resistance, this inhibition declines, causing selenoprotein levels and blood selenium levels to increase [Schomburg 2020].
Autoimmune Thyroiditis and Oxidative Stress and Selenium
In their review article, Winther, Rayman, and Bonnema [2020] state that oxidative stress – damage caused by an excess of harmful free radicals relative to antioxidants – has been implicated in the development of autoimmune thyroiditis. Accordingly, the antioxidant activity of such selenoproteins as the glutathione peroxidases and the thioredoxin reductases may explain the benefit of using selenium supplementation as a therapy for the disease [Winther 2020].
Filipowicz et al [2021] suggest that one beneficial effect of selenium supplementation may be the effect on the immune system and on oxidative stress in particular. They note that selenium is effective in reducing the a-TPO level in patients with hypothyroidism caused by autoimmune thyroiditis.
Note: a-TPO levels refer to the levels of thyroid peroxidase (TPO) antibodies in the blood. Thyroid peroxidase is an enzyme that is normal in the thyroid gland. It plays an important role in the production of thyroid hormones. If a TPO test detects antibodies against TPO in the blood, then that is an indication of an autoimmune thyroid disorder.
Autoimmune Thyroiditis and Hyperthyroidism and Selenium
Autoimmune thyroiditis is also associated with hyperthyroidism, which is the over-production of the thyroid hormones. Graves’ disease is the major cause of hyperthyroidism.
Various epidemiological studies have shown an association between the increased risk of Graves’ disease, an immune system disorder that results in hyperthyroidism, the overproduction of thyroid hormones, and low selenium status. In Graves’ disease patients, selenium supplementation might result in a faster remission of the hyperthyroidism and in improved quality of life [Winther 2020].
More information about the effect of selenium supplementation on the quality of life of autoimmune thyroiditis patients may come from the data of the CATALYST study, which was expected to wrap up in December 2021 [Filipowicz 2021]. The CATALYST study was designed to evaluate the extent to which supplementation with 200 mcg/day of SelenoPrecise® for 12 months would improve the patients’ quality of life [Winther 2014].
Summary: Selenium Status and Autoimmune Thyroiditis
The literature review conducted by Filipowicz et al [2021] shows that the use of selenium supplementation to prevent or delay autoimmune thyroiditis is supported by everyday clinical practice. The authors suggest that selenium supplement needs to be adjusted to the specific population’s profile, whether children, adults, males, females, pregnant women, or non-pregnant women. Particular attention needs to be paid to the availability of selenium in the local and regional diet and to the question of whether the patient has autoimmune thyroiditis or non-autoimmune thyroiditis thyroid disease.
The authors emphasize that pregnant females, and pregnant women from low iodine and low selenium regions, in particular, may be good candidates for selenium supplementation. Selenium supplementation of pregnant women may prevent the development of selenium deficiency, postpartum thyroiditis, hypertension, and poor neonatal outcomes [Filipowicz 2021].
Sources
Bügel S, Larsen EH, Sloth JJ, et al. Absorption, excretion, and retention of selenium from a high selenium yeast in men with a high intake of selenium. Food Nutr Res. 2008;52:10.3402/fnr.v52i0.1642.
EFSA Panel of Food Additives. Selenium-enriched yeast as a source for selenium added for nutritional purposes in foods for particular nutritional uses and foods (including food supplements) for the general population. 2008;766:1-42.
Filipowicz D, Majewska K, Kalantarova A, Szczepanek-Parulska E, Ruchała M. The rationale for selenium supplementation in patients with autoimmune thyroiditis, according to the current state of knowledge. Endokrynol Pol. 2021;72(2):153-162.
Schomburg L. The other view: the trace element selenium as a micronutrient in thyroid disease, diabetes, and beyond. Hormones (Athens). 2020 Mar;19(1):15-24.
Winther KH, Rayman MP, Bonnema SJ, et al. Selenium in thyroid disorders – essential knowledge for clinicians. Nat Rev Endocrinol. 2020; 16(3):165–176.
Winther KH, Watt T, Bjørner JB, et al. The chronic autoimmune thyroiditis
quality of life selenium trial (CATALYST): study protocol for a randomized
controlled trial. Trials. 2014;15:115.
The information presented in this summary article is not intended as medical advice and should not be used as such.
15 February 2022