Mineral
Selenium
The selenium content of a plant reflects the selenium in the soil it grew in, and that varies by more than a hundredfold across the world. It is one of the few nutrients where geography is the main variable.
What it does
Selenium is built into about twenty-five proteins, and in each of them it sits at the active site as selenocysteine — an amino acid the body assembles specifically for the purpose. The best-known family, the glutathione peroxidases, neutralise peroxides before they damage membranes.
A second family converts thyroid hormone from its storage form, T4, into the active form, T3. Thyroid tissue holds more selenium per gram than any other organ, which is a clue to how central this is.
It also supports immune function and, through the same antioxidant machinery, protects DNA from oxidative damage.
How much you need
| Who | Per day | Note |
|---|---|---|
| Infants, 0–6 months | 15 µg | Adequate Intake |
| Infants, 7–12 months | 20 µg | Adequate Intake |
| Children, 1–3 years | 20 µg | — |
| Children, 4–8 years | 30 µg | — |
| Children, 9–13 years | 40 µg | — |
| Ages 14 and over | 55 µg | — |
| Pregnancy | 60 µg | — |
| Breastfeeding | 70 µg | — |
The upper limit for adults is 400 µg a day, which is about seven times the recommendation — a narrower margin than most nutrients have. Two or three Brazil nuts a day is a sensible habit; a handful every day is not.
From our own data
The foods highest in selenium
Brazil nuts are in a category of their own and the reason is geological: they grow in Amazonian soil that happens to be selenium-rich. Everything else on the list is seafood, organ meat and, where the soil allows, wheat.
- 1
Pork kidney, braised566% · DV - 2
Black mustard seed298% · DV - 3
Pacific oysters, cooked280% · DV - 4
Mixed nuts, raw267% · DV - 5
Turkey skin, roasted262% · DV - 6
Flax seeds247% · DV - 7
Tuna, cooked205% · DV - 8
Sunflower seed butter, salted190% · DV - 9
Chicken giblets, fried189% · DV - 10
Semolina, enriched163% · DV - 11
Lobster146% · DV - 12
Wheat germ, raw144% · DV
Per 100 g, from our copy of USDA FoodData Central, against a Daily Value of 55µg. Ranked by amount, not by how much of it your body actually takes up — read the next section before you act on the order.
The table above is per 100 g. The app weighs the portion you actually ate.
What helps, and what gets in the way
Helps
- Variety of origin — food from several regions evens out what any one soil provides
- Seafood and organ meats, which concentrate it regardless of soil
- Vitamin E, with which it works closely against oxidative damage
Gets in the way
- Soil depletion, which is why the same crop varies enormously between countries
- Malabsorption conditions, particularly after bowel resection
- Dialysis, which removes it
Absorption is high — 80% or more — and largely unregulated, which is precisely why the upper limit matters. The body does not protect you from too much selenium the way it does from too much iron. Chronic excess causes selenosis: brittle hair and nails first, then gastrointestinal and neurological effects.
Who tends to fall short
Groups where intake or absorption is commonly lower than the reference. It is a list of populations, not a list of symptoms — it cannot tell you anything about yourself.
- People eating food grown in selenium-poor soil — parts of Europe, China and New Zealand
- People on long-term parenteral nutrition without supplementation
- People on dialysis
- People with severe gastrointestinal malabsorption
Cook it
Tuna, egg and Brazil nut salad
Two, ten minutes
Ingredients
- 1 tin tuna in olive oil, drained
- 2 eggs, soft-boiled
- 4 Brazil nuts, roughly chopped
- Two handfuls of watercress or rocket
- 1 tbsp olive oil
- Juice of half a lemon
- Black pepper
Method
- 1Boil the eggs to seven minutesInto already-boiling water, seven minutes exactly, then straight into cold. The yolk should be set at the edge and still soft in the middle.
- 2Chop the nuts coarselyFour is the number. Brazil nuts carry so much selenium that a larger handful every day would take you past the upper limit, which is not a sentence that applies to many foods.
- 3Dress the leaves firstOil, lemon and pepper tossed through the watercress before anything else goes in, so the leaves are coated rather than sitting in a puddle.
- 4AssembleTuna flaked over, eggs halved on top, nuts scattered last so they stay crunchy.
Four Brazil nuts is a portion, not a suggestion to be generous with. They are the single richest common food source of selenium and the gap between a useful amount and too much is unusually small.
Sources
- NIH Office of Dietary Supplements — Selenium
- Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium and Carotenoids
- USDA FoodData Central
This page is education, not medical advice. It does not diagnose anything and it is not a substitute for a clinician who knows your history. If you think you are short of selenium, the answer is a blood test and a conversation, not a supplement bought on the strength of an article.
Every food above, and 12,601 more, with the full panel — in the app.