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Thyroid Health, Selenium, and Geography

The thyroid gland, is a small, butterfly-shaped organ positioned at the front of the neck, is best known for being a metabolic powerhouse. This gland’s primary role is to secrete thyroid hormones, which regulate metabolism, protein synthesis, and healthy growth and development of children. Underactive (hypothyroid) and overactive (hyperthyroid) states result in the under- or overproduction of thyroid hormones, which cause a wide range of effects and symptoms that target numerous organ systems in the body (cardiovascular, gastrointestinal, endocrine, reproductive, metabolic rate, sleep, mood, etc). 

Autoimmune thyroid diseases, caused by a deleterious, misdirected immune cell attack on the body’s own thyroid gland can result in both hyperthyroid (ex. Graves’ Disease) and hypothyroid outcomes (ex. Hashimoto’s Thyroiditis). 

The specific cause of autoimmune thyroid diseases is still unknown; but, it has become quite evident that both environmental and genetic factors are strong contributors.   One in 10 Canadians suffers from a thyroid condition, women are more commonly affected than men, and there also seems to be significant disease correlation to geographic location. How does geography play a possible role in thyroid health? Let’s consider the case of selenium.

Selenium is an essential micronutrient and mineral. It is vital for appropriate immune system function, and plays a key role in thyroid health and activity. Selenium is combined with various proteins in the body to form enzymes, known as selenoproteins, that exert antioxidant and anti-inflammatory effects. As an antioxidant, selenoproteins protect thyroid tissue from oxidative damage, better known as free radical damage, a by-product of oxygen metabolism that causes cellular injury. The importance of selenium to thyroid health is underscored by the fact that the thyroid gland LOVES selenium so much, it has trouble letting it go! The thyroid contains the highest concentration of selenium in the body, which translates into the highest selenium content per gram of tissue.

Selenium deficient populations across the globe are associated with higher rates of autoimmune thyroid disease. An excellent study illustrates the importance of geographical variation of selenium in soil, and its impact on selenium blood status in study participants. The study was conducted in two cities in Shaanxi Province, China, where the populations shared genetic, environmental, and lifestyle similarities; they even had comparable iodine levels – yet differed significantly in their selenium status (adequate and low). This study concluded that the incidence of thyroid diseases was significantly lower in the selenium adequate city/population. This supported the hypothesis that higher selenium blood levels, associated with living in a selenium adequate region, may be thyro-protective.

Numerous studies have successfully also demonstrated that selenomethionine supplementation can reduce thyroid auto-antibody levels in the blood, in patients that require thyroid hormone supplementation, and in asymptomatic patient (euthyroid) populations. Selenomethionine has also been demonstrated to improve the symptoms and lower the auto-antibody levels in patients suffering from Graves’ Disease. Most selenium studies in patients with autoimmune thyroid diseases have used 200 μg/day of selenomethionine have yielded conflicting results. 

Therefore, the most recent reviews of the literature suggest that although selenium supplementation is beneficial for autoimmune thyroid conditions, the daily amount and treatment duration still hasn’t been validated.

Globally, selenium intake ranges from far too much (Nebraska, Dakota), to very little (parts of China, Russia, and Italy). Forms of selenium are found in soil, and enter the food chain through plants; this is a reflection of several variables: soil pH of the region, local organic-matter content, and the local forms of selenium found in the soil. Therefore, there is tremendous variability in selenium content in soils, and in the future, this may mirror a picture of population thyroid health as well.

The optimal intake of selenium believed to maximize optimal antioxidant capacity, and maximize blood levels of glutathione peroxidase, is 55 μg/day. Dietary sources of selenium are another way of increasing your daily intake of their essential mineral. Brazil nuts are one of the richest food sources of selenium. One ounce of Brazil nuts (6–8 nuts) can have up to 544 μg of selenium! Organ meats seafood, muscle meats, cereals, grains, mushrooms and dairy, are all good sources of selenium. Although selenium is considered essential, long-term, excessive intake can be toxic – better known as selenosis. Supplementation with greater than 200 μg/day although considered to be safe, should be implemented under the care of a physician or naturopathic doctor.


Hu, S., Rayman, M.P. (2017). Multiple Nutritional Factors and the Risk of Hashimoto’s Thyroiditis. Thyroid. 27 (5), 597-605.

Ferrari, S.M., Fallahi, P., Antonelli, A., Benevenga, S. (2017). Environmental Issues in Thyroid Diseases. Frontiers in Endocrinology. 8(50), 1-7.

Negro, R., Attanasio, R., Grimaldi, F., Marcocci, C., Guglielmi, R., Papini, E. (2016). A 2016 Italian Survey about the Clinical Use of Selenium in Thyroid Disease. European Thyroid Journal. 5, 164-170.

Negro, R., Attanasio, R., Grimaldi, F., Marcocci, C., Guglielmi, R., Papini, E. (2016). A 2016 Italian Survey about the Clinical Use of Selenium in Thyroid Disease. European Thyroid Journal. 5, 164-170.

Liontiris, M.I., Mazokopakis, E.E. (2017). A concise review of Hashimoto thyroiditis (HT) and the importance of iodine, selenium, vitamin D and gluten on the autoimmunity and dietary management of HT patients. Points that need more investigation. Hellenic Journal of Nuclear Medicine.20(1): 51-56.

About The Author

Darianna Berbenetz is a Naturopathic Medicine consultant, educator and Medical Advisor for AOR. She holds a Bachelor of Science degree from the University of Toronto, and Doctor of Naturopathic Medicine from the Canadian College of Naturopathic Medicine.

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