What it does in the body
- Antioxidant defense (glutathione peroxidase family)
- Thyroid hormone metabolism (T4 to T3 conversion)
- Immune function (enhanced NK cell activity, antibody production)
- DNA repair and cancer protection
- Male fertility (selenoprotein in sperm capsule)
How much you need (Daily Value)
| Group | Recommended | Source |
|---|---|---|
| Adult male | 55 mcg | NIH/IOM |
| Adult female | 55 mcg | NIH/IOM |
| Pregnancy | 60 mcg | WHO/IOM |
| Children | 20 mcg (1-3y), 30 mcg (4-8y), 40-55 mcg (9-18y) | NIH/IOM |
| Older adults | 55 mcg | NIH/IOM |
Richest food sources
| Food | Amount | Where |
|---|---|---|
| Brazil nuts | 1917 mcg per 100g (1 nut ≈ 70-90 mcg) | South America |
| Yellowfin tuna | 92 mcg per 100g | global oceans |
| Halibut | 47 mcg per 100g | North Pacific/Atlantic |
| Sardines | 53 mcg per 100g | Mediterranean |
| Chicken breast | 27 mcg per 100g | global |
| Eggs | 31 mcg per 100g | global |
| Sunflower seeds | 53 mcg per 100g | Americas/Europe |
| Brown rice (cooked) | 10 mcg per 100g | global |
In our food database, per 100 g
Highest among our free foods — open the Food Explorer to compare.
If you don't get enough
Mild: Subtle immune impairment, fatigue, muscle weakness, increased susceptibility to viral mutation (Coxsackievirus can become virulent in selenium-deficient hosts)
Moderate: Thyroid dysfunction (impaired T4 to T3 conversion), nail and hair changes, increased oxidative stress, male infertility
Severe: Keshan disease (fatal cardiomyopathy), Kashin-Beck disease (osteoarthropathy), myxedematous cretinism (with concurrent iodine deficiency)
Time to onset: Months to years for dietary deficiency. Keshan disease onset accelerated by concurrent viral infection.
Too much
Upper limit: 400 mcg/day (adults)
Selenosis: garlic breath odor, hair loss, nail brittleness/loss, nausea, diarrhea, peripheral neuropathy, skin rash. Acute toxicity can cause pulmonary edema and cardiac failure.
How well you absorb it
>80% for organic forms (selenomethionine, selenocysteine); 50-60% for inorganic forms (selenite, selenate)
Helped by: Protein (amino acid context improves absorption), Vitamins A, C, E (synergistic antioxidant network)
Hindered by: Heavy metals (mercury, cadmium, arsenic), High sulfur intake, Excessive selenium itself (auto-inhibition at high doses)
Cooking & storage
Selenium is relatively heat-stable but can be lost through boiling water (leaching). Selenium content of plant foods varies dramatically based on soil selenium content — the same food can vary 100-fold depending on growing region.
Nutrisize Health totals every nutrient from what you actually eat, against targets set for your age and sex, and flags what's short — across 4,995 foods, on your device.
