Selenium is an essential mineral the body uses to build selenoproteins, which have roles in thyroid hormone metabolism, DNA synthesis, reproduction and protection from oxidative damage. As a supplement it is used to cover low intake and has been studied for thyroid conditions, especially Hashimoto's thyroiditis.
Also known as: selenomethionine, sodium selenite, selenium yeast.
ODS lists a Recommended Dietary Allowance of 55 mcg a day for adults, 60 mcg in pregnancy and 70 mcg while breastfeeding. The Tolerable Upper Intake Level for adults is 400 mcg a day from food and supplements combined. Selenium-only supplements typically contain 100 to 400 mcg, and many multivitamins contain 55 mcg.
It is sold in the US as a dietary supplement. Under the 1994 dietary supplement law (DSHEA), FDA does not approve dietary supplements before they are marketed, and the maker, not FDA, is responsible for safety and labeling. There is no FDA-approved selenium pill for general use.
ODS says the body absorbs up to about 90% of the selenium in common supplement forms (selenomethionine, selenium yeast, sodium selenite and selenate). Long-term high intake causes selenosis: early signs are a garlic odor on the breath and a metallic taste, and the most common signs are hair loss and brittle or lost nails, along with rash, nausea, diarrhea, fatigue and irritability. Brazil nuts contain 68 to 91 mcg per nut. In 2008, 201 people had severe reactions to a liquid supplement that contained 200 times the selenium on its label.
On the thyroid, ODS says some trials found selenium lowered certain thyroid antibodies in people with chronic autoimmune (Hashimoto's) thyroiditis, while others found no effect on thyroid function or quality of life, and that the American Thyroid Association recommends against selenium supplements for pregnant women with thyroid autoimmunity. The chemotherapy drug cisplatin can lower selenium levels.
We could not find a single published half-life or time to peak for selenium that applies to a supplement dose, so we do not list one. The body builds selenium into proteins, and status is measured in blood, hair or nails over time rather than as a curve after one dose.
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