What are the signs of selenium deficiency?

Keshan disease, a heart muscle disease, appeared in parts of China where the soil carries almost no selenium.

Who is most likely to run low

Selenium deficiency on its own rarely causes obvious illness, and instead produces biochemical changes that leave people vulnerable when something else goes wrong.

What this means for you

The honest first line is that 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 shows up as a disease only where intake is extremely low and something else is going on.

Beyond that, selenium deficiency is a geographic condition rather than a dietary habit. It happens where the soil carries almost none, which historically meant a belt of regions in China and a few other places, and it barely exists in countries that import their grain.

The severe form has a name. Keshan disease damages the heart muscle and can cause heart failure, and it appeared in children and young women in affected areas. There is also Kashin-Beck disease, which damages joints and bones in some of the same regions.

Established. The evidence that selenium causes it is about as strong as nutritional epidemiology gets. Pooling community trials across 1,983,238 people in affected regions, giving selenium reduced Keshan disease by 86 per cent, with protection above 80 per cent in 35 of the 41 studies.

Low, but not low enough to be ill, is a real state

Europe sits lower in selenium than most people realise, and that shows up in an odd place. Graves' orbitopathy is an eye complication of an overactive thyroid, where the tissue behind the eyes swells and the eyes become sore and pushed forward. Four randomised trials, sifted out of 1,684 records, tested selenium against placebo in it. Selenium brought the clinical activity score down by 1.27 points at six months and left patients about two and a half times as likely to report a better quality of life, with the gains showing in vision and in mood.

Unsettled. Read the rest of that result before you do anything with it. Nothing measured on the eye itself moved. Bulging, soft tissue swelling and eye movement were all unchanged, so the score improved while the visible disease stayed put. There were four trials. All of them ran in European populations whose selenium was low to begin with, which is both the reason the finding belongs on a page about deficiency and the reason it may mean nothing for someone who already has enough.

Not for everyone. If you have thyroid eye disease, this is a conversation with the doctor treating it rather than a decision to make in a pharmacy. Selenium carries its own costs at higher intakes, and the trials above were run at a set dose for a set time under medical care.

Who might run low outside those regions

People on long-term dialysis, whose selenium levels are typically lower, and people fed intravenously without added selenium. Both are medical situations rather than something to diagnose from a symptom list, and the trials in dialysis found that supplements raised blood selenium without changing anything else that was measured.

For everyone else, a mixed diet with any fish, meat, eggs or grain covers 55 micrograms a day without effort.

One reason not to treat a suspected shortage with a large supplement. In five randomised trials, 200 micrograms of selenium a day raised the risk of type 2 diabetes by 11 per cent, and blood levels in the upper range track with more diabetes in observational data too. If you genuinely live where the soil is depleted, that is a conversation with a doctor about a measured dose rather than an argument for a bottle from a shelf.

If you eat no animal foods

A German trial gives the clearest recent look at this. The vegans in it started with a significantly lower estimated selenium intake than the omnivores alongside them. When both groups were given selenium, the rise in selenoprotein P was more pronounced in the vegans, which is what starting from lower down looks like. Both Brazil nut butter and a plain selenium supplement raised serum selenium and selenoprotein P, and the two worked equally well. If you have dropped animal foods and want to do something about selenium, either route has a trial behind it.

Not for everyone. Correcting a low intake is a different task from pushing it high, and the ceiling is closer than most pages admit. Europe re-derived its upper level in 2023 and put it at 255 micrograms a day for adults, including in pregnancy and breastfeeding, with hair loss as the effect that defines the limit. That sits 145 micrograms below the American 400 that English-language pages usually quote, this one included. A daily Brazil nut habit can cross the European figure on its own.

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.

Where to get it from food

• 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