Selenium
Supports thyroid hormone metabolism and antioxidant defenses.
Why it matters
Selenium is part of several selenoproteins that support antioxidant defenses, thyroid hormone metabolism, reproduction, and DNA synthesis.
- Supports antioxidant enzymes.
- Helps convert thyroid hormones into active forms.
- Supports reproduction and DNA synthesis.
If intake is too low
Selenium deficiency is uncommon in the United States, but when it happens it can affect thyroid function, immunity, and in severe cases the heart.
- Impaired thyroid hormone metabolism.
- Weaker immune function.
- Hair, nail, or muscle issues, and in severe deficiency heart problems can occur.
If intake is too high
Too much selenium can cause selenosis. Classic signs include brittle hair and nails, garlic breath, stomach upset, and nerve symptoms.
- Hair loss and brittle nails.
- Garlic breath, nausea, or diarrhea.
- Nerve symptoms when toxicity is prolonged.
Adult upper limit: 400 mcg/day
Selenium is one of the trace minerals where excess intake can become a real supplement problem.
Common food sources
Selenium is present in seafood, meats, eggs, grains, and especially Brazil nuts, but food content varies with soil.
- Brazil nuts
- Seafood, meat, and poultry
- Eggs, grains, and dairy foods
Who may need closer attention
Deficiency is uncommon in many U.S. diets, but excess is easier to create than people think.
- People using stand-alone selenium or thyroid blends
- People on very restricted diets
- Anyone who eats Brazil nuts often and also supplements selenium
Use extra caution if
Small details change the risk picture with nutrients more than most people expect.
You use selenium-specific thyroid or antioxidant products or eat Brazil nuts frequently. Selenium can overshoot its safe range quickly.
Supplement and label notes
Useful context when this nutrient shows up across more than one product.
- Brazil nuts can contain large amounts of selenium, so they count like a supplement in practice.
- Selenium often appears in thyroid formulas alongside iodine.
- If you already use a multivitamin, a separate selenium product may be unnecessary.
Daily Value targets in SuppMap
These are the same label-style Daily Value targets used in the app.
Official references
These pages were used to draft the summaries on this guide.
Educational only. These pages are not a diagnosis or a substitute for personal medical care.
More guides
Keep moving through the rest of the Daily Value chart from here.