This article is part of a special report on Thyroid Disorders. To see the other articles in this series, click here.
A healthy thyroid is a critical component of one’s overall health, and many people are struggling with thyroid disorders such as hypothyroidism, specifically Hashimoto’s autoimmune thyroiditis. In this autoimmune condition, the immune system attacks the thyroid gland, with the resulting inflammation leading to an underactive thyroid gland or hypothyroidism. Hashimoto’s disease is the most common form of hypothyroidism and was the first condition ever to be classified as an autoimmune disease.
I’ve written extensively about thyroid health, focusing on a multitude of environmental factors that may affect thyroid function, including gluten, gut health, stress, excess iodine, and vitamin D deficiency. I’ve also discussed why dietary changes are always the first step in treating Hashimoto’s, and why replacement thyroid hormone is often necessary for a successful outcome.
There is yet another nutritional factor that may play a role in thyroid health: selenium.
Selenium deficiency is not thought to be common in healthy adults, but is more likely to be found in those with digestive health issues causing poor absorption of nutrients, such as Crohn’s or celiac disease, or those with serious inflammation due to chronic infection. (1, 2) It is thought that selenium deficiency does not specifically cause illness by itself, but that it makes the body more susceptible to illnesses caused by other nutritional, biochemical or infectious stresses, due to its role in immune function. (3) Adequate selenium nutrition supports efficient thyroid hormone synthesis and metabolism and protects the thyroid gland from damage from excessive iodine exposure. (4)
Several research studies have demonstrated the benefits of selenium supplementation in treating autoimmune thyroid conditions. One study found that selenium supplementation had a significant impact on inflammatory activity in thyroid-specific autoimmune disease, and reducing inflammation may limit damage to thyroid tissue. (6) This may be due to the increase in glutathione peroxidase and thioredoxin reductase activity, as well as the decrease in toxic concentrations of hydrogen peroxide and lipid hydroperoxides which result from thyroid hormone synthesis. (7)
Another study followed patients for 9 months, and found that selenium supplementation reduced thyroid peroxidase antibody levels in the blood, even in selenium sufficient patients. (8) While these studies show promise for the use of selenium supplementation in preventing thyroid tissue damage, further research is needed to determine the long-term clinical effects of selenium treatment on inflammatory autoimmune thyroiditis.
Additionally, selenium is also essential for the conversion of T4 to T3, as deiodinase enzymes (those enzymes that remove iodine atoms from T4 during conversion) are selenium-dependent. As I’ve explained before, T3 is the active form of thyroid hormone, and low T3 can cause hypothyroid symptoms. A double-blind intervention study found that selenium supplementation in selenium deficient subjects modulated T4 levels, theoretically by improving peripheral conversion to T3. (9) In cases of severe selenium deficiency, conversion of T4 to T3 may be impaired, leading to hypothyroid symptoms. As T3 conversion is not performed by the thyroid, the dependence on selenoproteins for this conversion demonstrates how significant selenium deficiency could lead to hypothyroid symptoms.
So the question is, should you start supplementing with selenium if you have hypothyroidism, Hashimoto’s thyroiditis, or low T3 levels?
As the answer often is, it depends. These preliminary studies show the positive effects of selenium supplementation on inflammatory activity in autoimmune thyroid conditions, but the long term effects of supplementation on thyroid health are still unknown. And we know that selenium is an essential component of the enzymes that convert T4 to T3, but whether supplementation will increase serum T3 levels is unclear.
While it seems that selenium supplementation would be an obvious solution to poor thyroid function, long term consumption of high doses of selenium can lead to complications such as gastrointestinal upsets, hair loss, white blotchy nails, garlic breath odor, fatigue, irritability, and mild nerve damage. (10) Additionally, supplementing selenium in the context of low iodine status may actually aggravate hypothyroidism. Mario Renato Iwakura discusses this particular topic extensively on Paul Jaminet’s Perfect Health Diet blog.
Moreover, a large clinical trial examining the effects of selenium supplementation on prostate cancer risk in over 35,000 men found that those with normal to high selenium levels at baseline experienced a significant increase in the risk of prostate cancer after supplementing with 200 mcg/d of selenium. For more details on this study, see my article “Important Update on Selenium Supplementation“.
For now, the best option for most people may be to include selenium-rich foods in the context of a healthy Paleo diet. Great sources of selenium include: brazil nuts, crimini mushrooms, cod, shrimp, tuna, halibut, salmon, scallops, chicken, eggs, shiitake mushrooms, lamb, and turkey. Brazil nuts are particularly rich in selenium; it only takes one or two per day to improve your selenium status and boost immune function. (11)
Making sure your selenium intake is optimal may give your immune system and thyroid the boost it needs to help it function better. It is especially important for those managing thyroid conditions to ensure their selenium status is adequate.
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