Selenium and Your Thyroid

Selenium is an essential trace mineral, which means that we need to get some of it through our diets in order to live and also to thrive.  We need only a tiny amount–measured in micrograms (one millionth of a gram)–but clearly some people do not get even that small amount.

Selenium is highly concentrated in the thyroid gland, and plays a crucial role in proper thyroid function. It is an essential part of the enzyme that catalyzes the conversion of T4, the inactive form of thyroid hormone, to T3, the active form of thyroid hormone. By doing so, it regulates the concentration of the active hormone.

Selenium also is an essential part of an important group of protective, antioxidant enzymes, glutathione peroxidases. These enzymes help to neutralize hydrogen peroxide in your body (the same bubbly stuff you might use to clean a wound.) Hydrogen peroxide is produced in the thyroid gland as a byproduct of T4 biosynthesis, and, over time, can directly damage thyroid cells if not neutralized.  Several selenium-containing compounds (called selenoproteins) participate in the protection of thyrocytes from damage by hydrogen peroxide.

Lower serum selenium levels have been seen in people with thyroid inflammation and autoimmunity against the thyroid, and in some studies, selenium supplement has reduced levels of thyroid antibodies by 40-70%. In fact, a two-year clinical trial has just started in Denmark to see if taking 100 micrograms (mcg.) twice a day of supplemental selenium is helpful for people being treated for Graves hypothyroidism, an autoimmune disease.

If you have thyroid problems, and especially if you have an autoimmune thyroid condition, it’s a good idea to make sure you are getting adequate selenium in your diet and from supplements.

The National Research Council has set an estimated safe and adequate daily intake for adults of 50 to 200 mcg. They also calculated a Safe Upper Limit of 400 mcg. a day, though most people have no difficulties taking twice that amount.

In the U.S., people are generally assumed to get an adequate amount of selenium from foods, because that is what the biggest dietary survey (NHANES) has found. Men have an average intake of 100 mcg. and women 70 mcg. a day. However, research that measured glutathione peroxidase activity in the body found that it reached maximum activity (then leveled out) when people were getting about 30 mcg. of selenium in addition to what they are getting from foods. So an optimal amount of selenium for antioxidant protection may be may more than what the US government considers an adequate amount.

It is very reasonable for people with thyroid problems to take an additional 200 mcg. of selenium from supplements in addition to what they get from foods. It’s important to take a form that is readily absorbable, an amino acid chelate such as selenomethionone or selenocysteine.

The best food sources of selenium are organ meats such as liver, and seafood, followed by “muscle” meats. Cereals, dairy products and fruits and vegetables also contain small amounts, but you can’t count on them alone to get enough, and amounts vary widely. Brazil nuts are a good source, with 70-90 mcg. per nut! Mushrooms–especially wild and Asian varieties–and garlic are also decent sources, provided they are grown in selenium-rich soil.

REFERENCES
Köhrle J, Jakob F, Contempré B, Dumont JE. Selenium, the thyroid, and the endocrine system. Endocr Rev. 2005 Dec;26(7):944-84.

Schomburg L.  Selenium, selenoproteins and the thyroid gland: interactions in health and disease. Nat Rev Endocrinol. 2011 Oct 18;8(3):160-71.

Shils ME, Shike M, Ross AC et al. Modern Nutrition in Health and Disease (11th ed.) Lippincott Williams & Wilkins (Philadelphia) 2012.

Watt T, Cramon P, Bjorner JB, et. al. Selenium supplementation for patients with Graves’ hyperthyroidism (the GRASS trial): study protocol for a randomized controlled trial. Trials. 2013 Apr 30;14:119. doi: 10.1186/1745-6215-14-119.