Brazil nuts are the food highest in selenium. USDA data puts them at 1,920 micrograms per 100 grams, six times the next food on the list, braised pork kidney at 312. Among the foods most men actually eat, seafood leads: tuna, mussels, oysters and sardines. The catch is that selenium in food tracks the soil it grew in, so any chart is a guide.
That last part is the bit most food lists leave out. Two bags of the same nut can differ by a factor of ten. Two loaves of bread can too. The ranking below is still the right place to start, as long as you read the numbers as central estimates.
The short version
- Brazil nuts top every list at 1,920mcg per 100g.
- Seafood, organ meat and eggs lead among everyday foods.
- Adults need 55mcg a day. The UK sets men at 75mcg.
- The upper limit is 400mcg, and Brazil nuts vary enormously.
- US wheat carries about ten times the selenium of UK wheat.
What food is highest in selenium, ranked per 100g
Every figure below comes from the USDA FoodData Central SR Legacy dataset, per 100 grams, cooked unless stated. Each food name links to its USDA search record. These are US-grown values, which matters more than it sounds (see the soil section further down).
| Food | Selenium (mcg per 100g) |
|---|---|
| Brazil nuts, dried | 1,920 |
| Pork kidney, braised | 312 |
| Lamb kidney, braised | 219 |
| Yellowfin tuna, cooked | 108 |
| Blue mussels, cooked | 90 |
| Oysters, farmed, cooked | 78 |
| Sunflower seeds, dried | 53 |
| Sardines, canned in oil | 53 |
| Atlantic mackerel, cooked | 52 |
| Wild Atlantic salmon, cooked | 47 |
| Atlantic cod, cooked | 38 |
| Beef liver, braised | 36 |
| Pork loin, roasted | 36 |
| Egg, hard-boiled | 31 |
| Turkey breast, roasted | 30 |
| Cheddar cheese | 28 |
| Whole-wheat bread | 26 |
| Chicken breast with skin, roasted | 25 |
| Beef mince, cooked | 21 |
| Brown rice, parboiled, cooked | 9 |
| Whole milk | 4 |
| Lentils, cooked | 3 |
| Spinach, cooked | 2 |
| Kidney beans, cooked | 1 |
The pattern is easy to read. Seafood and meat cluster between 20 and 110. Plants, Brazil nuts and seeds aside, mostly sit in single figures. A 100g portion of tuna at 108mcg covers the 55mcg adult requirement about twice. The same weight of lentils at 3mcg barely registers.
A plate of fish, or eggs at 31mcg per 100g alongside some meat, gets most men most of the way there. Worth knowing before you buy anything.
Brazil nuts: the richest source, and the least predictable
The 1,920 figure is an average, and the spread behind it is wild. A 1995 study in Chemosphere analysed 162 nuts from each of two Brazilian regions, one nut at a time. Nuts from Acre-Rondonia averaged 3.06 micrograms of selenium per gram, with a range of 0.03 to 31.7. Nuts from Manaus-Belem averaged 36.0, with a range of 1.25 to 512.
So the average nut from one region carried roughly twelve times the selenium of the average nut from the other. At the very top of that range of 512 micrograms per gram, a single gram of nut holds more than the 400 microgram daily upper limit. The bag in your cupboard does not tell you which region it came from.
The good news is that ordinary amounts work. A 2008 randomised trial in the American Journal of Clinical Nutrition gave 59 New Zealand adults two Brazil nuts a day for 12 weeks. The nuts were expected to supply about 100mcg. Measured intake averaged 53mcg, somewhere between 20 and 84 depending on the nut. Plasma selenium rose 64.2% in the nut group, against 61.0% for 100mcg of selenomethionine and 7.6% for placebo.
In English: two nuts a day did the same job as a selenium supplement. One or two is the useful dose. A daily handful is where it stops being useful.
Why the same food can carry ten times the selenium
Plants take up whatever selenium the soil offers, so a crop mirrors its field. A review from the British Geological Survey in the Proceedings of the Nutrition Society notes that most rocks at the Earth's surface are low in selenium, which is why most soils are too.
The same review has the detail that matters most for anyone in Britain. US wheat carries about ten times more selenium than UK wheat, because the American wheat belt sits on richer soil. The review discusses the recent fall in UK selenium intake alongside bakers using less North American wheat. The bread row in the table above is a US loaf. A British one is likely to come in lower.
Soil is also shifting. A 2017 study in PNAS modelled 33,241 soil data points and estimated that up to one in seven people worldwide have a low dietary selenium intake. Under moderate climate scenarios for 2080 to 2099, the authors predicted soil selenium would fall, particularly on farmland.
Finland is the proof that the soil really is the lever. Its soils are poor in available selenium, so since 1984 the country has added it to farm fertiliser. Within two years, mean selenium intake tripled and serum selenium rose 70%. Every major food group rose except fish, which is one reason seafood is the steadier bet wherever you live.
How much selenium you actually need
The US recommended intake for adults is 55mcg a day, with a tolerable upper limit of 400mcg. The UK sets a higher reference intake of 75mcg for men and 60mcg for women. The same 2004 paper reported that UK surveys put average intakes at 30 to 40mcg a day, well below either figure.
The window between enough and too much is narrow, and more is not automatically better. A 2012 Lancet review by Margaret Rayman describes a U-shaped link between selenium status and health. Extra selenium may help people whose status is low. People whose status is already adequate to high might be affected adversely, and the review says they should not take selenium supplements. Supplementing people who already get enough might raise their risk of type 2 diabetes.
Which means the practical question is simple. Are you likely to be low? You probably are if several of these apply:
- You rarely eat fish, shellfish, eggs or meat, the foods that lead the table above.
- You live in the UK and most of your grain is home-grown, given the tenfold wheat gap.
- You live somewhere with falling intakes, which a 2000 Lancet review flagged in several European countries.
- You avoid nuts, so Brazil nuts never enter the picture.
What to actually do about it
Food first. Fish or shellfish a couple of times a week and eggs most days put most men comfortably near the requirement, based on the USDA values above. If you like Brazil nuts, one or two a day matched a 100mcg selenomethionine supplement in the Thomson trial. Stop there.
Be careful about stacking. Daily Brazil nuts plus a standalone high-dose selenium tablet plus a multivitamin is how people drift toward the 400mcg ceiling without noticing. Count every source before adding one.
Selenium also has a partner. Your thyroid builds its hormone from iodine, and selenoproteins are involved in the production of active thyroid hormone. If you have read our piece on iodine deficiency, you know the two travel together. For the rest of what selenium does in the body, see the five jobs selenium actually does.
If you want a steady floor under all this, Fireblood contains 25mcg of selenium as L-selenomethionine, the same form used in the comparison arm of that Brazil nut trial. That is under half the 55mcg requirement on purpose. Rayman's U-curve is the reason we did not put 200 in the tub. Food does the rest.
The number on the chart describes the field
Ask what food is highest in selenium and the answer is Brazil nuts, every time. The more useful answer is that the figure next to any food tells you about the soil it came from. Eat the fish, and keep the nuts to one or two.
Fireblood contains 25mcg of selenium as L-selenomethionine and 75mcg of iodine alongside 37 other nutrients, every dose printed on the label with no proprietary blends. It covers the everyday gaps in a diet that is already doing most of the work. The full formula is here if you want to check it against what you already take.
Header photo: Brazil nuts by Henning Schlottmann, Wikimedia Commons, CC BY-SA 4.0.
