How much selenium do you need per day?

The RDA for selenium is 55 mcg a day for adult men and women.

These are the reference amounts used on US food labels and in dietary guidance, not personal targets. What you need shifts with age, pregnancy, medication and health conditions. The % Daily Value shown on every food page here is calculated against the FDA Daily Value for selenium, which is 55 µg a day.

What this means for you

Fifty-five micrograms a day, and in most countries you are already there without trying. Fish, shellfish, meat, eggs, dairy and whole grains carry it, and one portion of rockfish on this site covers two days at once.

Selenium is unusual in one way that is worth knowing. The amount in plant foods depends on the soil they grew in rather than on the plant, so the same bread can carry very different amounts in different countries. That is also why the deficiency, where it exists, is geographic rather than dietary.

Established. Where the soil has almost none, the consequences are severe and the fix works. Across community trials covering 1,983,238 residents of affected regions in China, giving selenium cut the rate of Keshan disease, a heart muscle disease, by 86 per cent.

Myth. Adding selenium on top of an adequate intake is a different question, and it was tested properly. In the randomised trials with a low risk of bias, selenium supplements left cancer risk unchanged, with a risk ratio of 1.01 on high-certainty evidence. The largest trial found more high-grade prostate cancer in men who already had plenty of selenium, and slightly more type 2 diabetes.

The dose curve bends both ways

Twenty-seven randomised trials were pooled recently to draw the whole dose-response curve instead of arguing about a single threshold, and the curve came out U-shaped. In people who started with the lowest intakes, extra selenium looked beneficial. From 200 micrograms a day upwards it turned: HDL and LDL cholesterol fell and triglycerides rose, and the same pattern showed up once the selenium in blood passed roughly 150 micrograms per litre. The turn was sharpest in healthy participants, in trials running longer than three months, and in European groups taking more than 300 micrograms a day. Inorganic selenium behaved worse than organic.

Unsettled. That U shape is why a single answer to the question does not exist. The same capsule helps or harms depending on where you started, and hardly anyone knows where they started, because selenium in food follows the soil rather than the label. What survives from it in practice is narrow. Fifty-five micrograms is the floor, ordinary food in most countries clears it, and the extra on top is the part with a measured downside attached.

The one food to count rather than eat freely

Brazil nuts carry 68 to 91 micrograms each, so two of them exceed a day's requirement and a handful every day approaches the ceiling of 400 micrograms. Long-term excess shows up as hair loss, brittle nails and a garlic smell on the breath.

One last thing about the floor rather than the ceiling. Selenium deficiency on its own rarely causes obvious illness. It produces biochemical changes that leave people vulnerable when something else goes wrong, which is why it became a disease only where the soil carried almost none and life was hard in other ways too.

The 55 micrograms is a floor, and the interesting question is how far above it you can go before the arithmetic turns against you. The clearest answer comes from diabetes rather than from hair loss: across five randomised trials, 200 micrograms a day raised the risk of type 2 diabetes by 11 per cent. That dose is below the 400 microgram ceiling and well above the requirement, which is exactly the range most selenium supplements sell in.

The recommendation is questioned by the people who tested it

Unsettled. The 55 microgram figure was set using one marker of selenium status, the enzyme glutathione peroxidase, and the intake at which it stops rising. A trial in a low-selenium part of China measured a second marker alongside it, selenoprotein P, and that one never reached full expression at any dose in either form of selenium given, while glutathione peroxidase saturated far below. The authors concluded that selenoprotein P is the better indicator and that the recommendation built on the other marker should be revised. It has not been revised. So the number on this page is the number in use, and the people who looked at it hardest think it sits in the wrong place.

The same trial showed the form matters more than the milligrams suggest. Selenium bound into an amino acid, selenomethionine, was absorbed about twice as well as the mineral salt. Full glutathione peroxidase took 37 micrograms a day as selenomethionine against 66 as selenite. Selenium in food is mostly the amino acid kind. A cheap supplement is often the salt.

For most readers the question is settled by what they already eat. The median American intake is 92 micrograms a day, 96 among adults, with the 95th percentile at 227 and the fifth at 32.

Not for everyone. If your plan for reaching the number is a daily Brazil nut, read the ceiling first. Europe re-derived its upper level in 2023 and set it at 255 micrograms a day, against the American 400 this page has used, and one 5 gram nut carries about 96 micrograms. A 28 gram handful carries 537 and clears both. Brazil nuts also take natural radium out of the soil, which works out at about 165 microsieverts a year at 15 grams of nut butter a day, against roughly 300 microsieverts from all other food. That is a small addition and it is worth knowing before a habit becomes daily.

Written from the evidence cards and the data on this page, then checked back against the sources. Bioma Learn has no human medical reviewer at this time and we say so rather than invent one. Information, not medical advice. How we verify.

Foods highest in selenium on this site

• Rockfish, Pacific, mixed species, cooked — 113.5 µg per 1 fillet (206% DV)
• Lobster, northern, cooked — 106 µg per 1 cup (193% DV)
• Sunflower seed kernels, oil roasted — 105.6 µg per 1 cup (192% DV)
• Sunflower seed kernels, dry roasted — 102.1 µg per 1.0 cup (186% DV)
• Sunflower seed kernels from shell, dry roasted — 101.5 µg per 1 cup (185% DV)

All selenium sources ranked →

Full guide: Selenium: a deficiency that kills and a supplement that does not help