Vitamins and minerals are essential for maintaining normal body system function and for providing protection from oxidative damage. Selenium acts as a strong antioxidant in addition to a diverse range of other activities conducted in the body. Selenium can be consumed in the diet or in supplemental form.
Selenium is an essential mineral, and in addition to its role as an antioxidant, selenium is crucial for thyroid hormone metabolism, DNA synthesis, reproduction, and immune function.5 Selenium exhibits a wide range of functions across body systems due to its presence in 25 distinct selenoproteins (proteins containing selenium). Selenium has also been identified in five glutathione peroxidase enzymes, which are an integral part of antioxidation. These have been found in the thyroid gland, lining of the lungs and intestines, kidneys, olfactory system, and testes (selenium is also crucial for sperm production and motility).1
Some glutathione peroxidases are essential for liver detoxification and other antioxidant functions. In thyroid metabolism, the inactive form of thyroid hormone, thyroxine (T4), is converted to the active form triiodothyronine (T3) by removing an iodine molecule. This reaction is catalyzed by a selenium dependent enzyme.
Sources of Selenium
The NIH Office of Dietary Supplements currently recommends a daily intake of 55mcg daily selenium for all people 14 years and older. Brazil nuts, seafood, and organ meats are strong sources of dietary selenium. Just one ounce of Brazil nuts contains approximately 544mcg of selenium, well over the RDA.5 Some grains and dairy also contain selenium. For plant sources, like grains and Brazil nuts, the selenium levels will vary by region due to the soil concentration of selenium for plant uptake.2 Selenium is also readily available in mineral supplements.
It is estimated that the majority of Americans consume adequate selenium levels. Those at risk for deficiency include people living in regions with low selenium soil levels, those undergoing kidney dialysis, or people with HIV.2 Selenium deficiency is associated with male infertility and may also worsen iodine deficiency, increasing cretinism risk in infants.2
Selenium and Thyroid Function
There are high concentrations of selenium in the thyroid gland, and many selenoproteins help to regulate thyroid function. Selenium deficiency is thus associated with thyroid dysfunction and related conditions such as autoimmune thyroiditis (Hashimoto thyroiditis) and mild Graves’ disease. Studies find that adequate selenium intake as well as optimally balanced levels of iodine and iron maximize the chance of healthy thyroid function.3
Reduced Risk for Cardiovascular Disease
The link between selenium and cardiovascular disease has been studied for decades. As selenoproteins act as enzymes to help to generate DNA and prevent cell damage, they may also minimize inflammation and platelet aggregation by reducing the oxidative modification of lipids, thus ultimately reducing the overall risk for cardiovascular disease. Selenium has also been considered as a biomarker in coronary heart disease.4