Selenium RDA Table
| Life stage | RDA (mcg/day) |
|---|---|
| Infant 0–6 mo | 15 (AI) |
| Infant 7–12 mo | 20 (AI) |
| 1–3 years | 20 |
| 4–8 years | 30 |
| 9–13 years | 40 |
| 14–18 years | 55 |
| 19+ years | 55 |
| Pregnancy | 60 |
| Lactation | 70 |
| Upper limit, adult | 400 (EFSA: 255) |
| Food | Portion | mcg | %DV |
|---|---|---|---|
| Brazil nuts (6–8 nuts) | 1 oz | 544 | 989% |
| Tuna, yellowfin, cooked | 3 oz | 92 | 167% |
| Sardines, canned in oil | 3 oz | 45 | 82% |
| Shrimp, cooked | 3 oz | 42 | 76% |
| Pork chop, cooked | 3 oz | 37 | 67% |
| Beef steak, bottom round | 3 oz | 37 | 67% |
| Turkey, roasted | 3 oz | 26 | 47% |
| Chicken breast, roasted | 3 oz | 22 | 40% |
| Cottage cheese, 1% milkfat | 1 cup | 20 | 36% |
| Egg, hard-boiled | 1 large | 15 | 27% |
Selenium is the mineral where one single food breaks the whole table: a 1-ounce handful of Brazil nuts carries about 544 mcg - 989% of the Daily Value, nearly ten days of the adult RDA - and each individual nut varies from 68 to 91 mcg, so one nut is a full day and four can flirt with the 400 mcg adult ceiling. No other nutrient on this family of tables has a food that overshoots the requirement by an order of magnitude.
The deficiency story is not an American story. Average US intake runs about 108 mcg a day from food alone - almost twice the 55 mcg RDA - because the Great Plains sit on selenium-rich soil. The real deficiency map is agricultural: Keshan disease, a fatal heart-muscle disease, haunted rural China where soil delivers as little as 10 mcg a day, and ensuring intakes above 20 mcg protects against it. Your selenium level is your region's geology before it is your diet.
The supplement chapter ends badly: the SELECT trial followed 35,533 men and found selenium supplements did not reduce prostate cancer, with hints of increased risk in men who already had plenty. The NIH's summary for men over 55 is blunt - avoid selenium supplements above dietary intakes. Meanwhile selenosis (chronic toxicity) announces itself unmistakably: garlic breath without garlic, brittle nails, hair loss, a metallic taste.
How to use
- Find your row: 55 mcg for men and women from age 19; 55 for teens 14-18; 40 at 9-13; 30 at 4-8 and 20 at 1-3; pregnancy 60 and breastfeeding 70 at every adult age.
- Cover it with the sea-and-meat shelf: tuna (92 mcg per 3 oz), sardines or shrimp (45/42), pork chop or beef steak (37), turkey, chicken, eggs and cottage cheese in normal portions - an omnivore crosses 55 mcg by dinner without trying.
- Treat Brazil nuts as a dose, not a snack: one nut is 68-91 mcg, a day's supply; a daily handful of six-to-eight is 544 mcg on the label alone and pushes chronic intake toward the 400 mcg ceiling - the NIH note that regular consumption could cause selenium toxicity refers to exactly this habit.
Frequently asked questions
How much selenium do I need per day?
The NIH RDA is 55 mcg for men and women from 19, 55 for teens 14-18, 40 for ages 9-13, 30 at 4-8 and 20 at 1-3, with 15-20 mcg adequate-intake values in infancy. Pregnancy raises it to 60 mcg and breastfeeding to 70. The ceiling (UL) is 400 mcg a day for everyone 13 and up - and Europe's food-safety agency set its own adult limit at 255 mcg, lower than the US number, which tells you the safety margin above one Brazil nut is thinner than supplement labels imply.
How many Brazil nuts can I eat a day?
One is the honest answer. Each nut carries 68-91 mcg depending on the tree and the soil, so a single nut covers a full adult day (55 mcg) with room to spare; a 1-ounce serving of 6-8 nuts is 544 mcg - 989% of the Daily Value and over the 400 mcg UL in a single sitting. That is not dangerous once, but the NIH flags regular consumption of Brazil nuts as a route to selenium toxicity. Treat the bag like a supplement bottle with a serving size of one.
What does selenium do for the thyroid?
The thyroid holds more selenium than any other organ, and its selenoproteins do the work of converting the storage hormone T4 into the active T3 that sets your metabolic rate. That is why selenium status and thyroid function travel together - but the trials do not reward supplementation: the American Thyroid Association actually recommends against selenium supplements for pregnant women with thyroid autoimmunity, after early hopes. If your thyroid is healthy and your diet includes fish, meat, eggs or grains from varied regions, you are covered.
What are the signs of too much or too little selenium?
Too much (selenosis, from chronic intake above the 400 mcg UL): garlic breath with no garlic in sight, brittle or losing nails, hair shedding, a metallic taste, nausea and irritability - the classic outbreak came from a 2008 misformulated supplement that delivered roughly 200 times its labeled amount to 201 people. Too little is regional, not dietary: Keshan disease (heart muscle) and Kashin-Beck disease (joints) occur where soil supplies under about 10-20 mcg a day; in the US the average intake of 108 mcg makes true deficiency rare without underlying disease.
Should men take selenium supplements for prostate health?
No - this is the best-studied question in the file. An early secondary analysis in men with low baseline selenium suggested a 49% lower prostate-cancer risk at 200 mcg a day, which launched the SELECT trial: 35,533 men, and no reduction in prostate cancer at all, plus a hint of more high-grade disease among men who started with high selenium status. The NIH conclusion for men over 55: do not take selenium above what you eat. Food first, and given the average American diet, probably not even that.