What it is
Selenium is a trace element built into selenoproteins that take part in antioxidant defence, thyroid hormone metabolism and reproduction. The recommended intake for adults is 55 mcg per day. It is sold mostly for the thyroid and immunity.
What the label does not say
- The gap between the recommended intake (55 mcg) and the upper limit (400 mcg) is counted in micrograms. The combined total of food, multivitamin and dedicated supplement crosses it faster than with most minerals.
- The NIH lists 544 mcg of selenium per ounce of Brazil nuts, or about 68 to 91 mcg per nut. A single ounce on its own exceeds the upper limit of 400 mcg, and the NIH writes that these nuts could cause selenium toxicity if eaten regularly.
- The content of a plant food depends on the amount and form of selenium present in the soil, and the NIH specifies that concentrations vary widely by geographic location. The same food therefore does not provide the same dose from one batch to the next.
The forms on the shelf
- Selenomethionine and selenium-enriched yeast: organic forms, the most common in supplements.
- Sodium selenite and sodium selenate: inorganic forms. The NIH indicates that the body absorbs up to about 90% of ingested selenium.
- Multivitamins: often already contain it, which adds to a dedicated supplement.
Published reference values
- Recommended intake for adults: 55 mcg per day, men and women.
- Upper limit: 400 mcg per day for adults.
- Above that, selenosis is described by hair loss, brittle nails, garlic breath, a metallic taste, skin rash, nausea and diarrhea.
When
Can be taken at any time. The real question is not the hour, but the combined total of food, a multivitamin and a dedicated supplement.
To mention to a professional
- Thyroid disorder, regular consumption of Brazil nuts, taking a multivitamin containing selenium at the same time, pregnancy and breastfeeding: check with a health care professional.
What it is sold for, and what the data show
Selenium is sold for the thyroid, immunity and longevity. Correcting an insufficient intake makes sense, but the NIH fact sheet describes no clear benefit from a supplement in someone whose intake is already adequate, and the margin before the upper limit is narrow. It is one of the few nutrients where taking more backfires quickly.
From the plate first
Protein-rich foods are the most concentrated: Brazil nuts (highly variable), seafood, meats, poultry and organ meats. Grains, eggs and dairy products provide it too.
Sources
- NIH Office of Dietary Supplements, Selenium (Health Professional)
- Health Canada, Dietary Reference Intakes, reference values for elements
Educational information, drawn from the sources above. It does not replace the advice of a health professional, who remains the reference for your situation, your medications, pregnancy or breastfeeding.