Selenium is found in a wide range of foods, with the richest sources being Brazil nuts, seafood, organ meats, and whole grains. Most people get enough from a varied diet, but the amount in any given food depends heavily on where it was grown or raised, because selenium levels in soil vary dramatically by region.
The Richest Food Sources of Selenium
Brazil nuts are the single most concentrated food source of selenium on the planet. The average Brazil nut contains roughly 31 micrograms of selenium per gram of nut, though this can range from 8 to 83 micrograms per gram depending on where the tree grew. That means just one or two Brazil nuts can meet your entire daily requirement, and eating a handful regularly could push you into excessive territory.
Seafood is another reliable source. A 3-ounce serving of canned white tuna provides about 51 micrograms of selenium, which nearly covers the full daily recommendation on its own. Fresh skipjack tuna delivers around 40 micrograms per serving. Other fish like halibut, sardines, and shrimp are also solid contributors.
Beyond nuts and fish, you’ll find meaningful amounts of selenium in eggs, chicken, turkey, beef, pork, and cottage cheese. Organ meats like liver tend to be especially rich. Among plant foods, whole grains, sunflower seeds, mushrooms, and legumes all contribute selenium, though the amounts are more variable.
Why the Same Food Can Have Different Amounts
Selenium enters the food chain through soil. Plants absorb it from the ground, animals eat those plants, and the mineral works its way up. The catch is that soil selenium levels are wildly uneven across the globe. Some regions have naturally selenium-rich soil, while others, particularly parts of China, New Zealand, and certain areas of Europe, have very low concentrations. Crops grown in selenium-poor soil will contain less of it, regardless of the crop type.
The form selenium takes in soil also matters. When it exists as free, water-soluble compounds, plants can absorb it readily. But when selenium binds tightly to organic matter or gets locked into mineral structures, it becomes far less available for plant uptake. This is why two wheat fields in different regions can produce grain with vastly different selenium content, even if the total selenium in the soil looks similar on paper.
In countries like the United States, where food is sourced from many regions and shipped widely, this geographic variability tends to average out. In countries where food is grown and consumed locally, deficiency is a more realistic concern.
How Much You Need Each Day
The recommended daily intake for adults is 55 micrograms. Pregnant women need slightly more, at 60 micrograms. The tolerable upper limit, the maximum you should consume from food and supplements combined, is 400 micrograms per day for adults. Staying between those two numbers is the sweet spot.
Your Body Absorbs Some Forms Better Than Others
Selenium in food comes in two main forms: an organic form found naturally in plant and animal proteins, and inorganic forms often used in supplements. Your body absorbs the organic form, which is built into the amino acid structure of proteins, roughly twice as efficiently as the inorganic version. This is one reason why getting selenium from food rather than supplements tends to be more effective. Animal proteins like fish, poultry, and eggs deliver selenium in this more absorbable form.
What Selenium Does in Your Body
Selenium isn’t just passing through. It gets incorporated into specialized proteins that perform critical jobs. One of the most important involves your thyroid gland, which contains more selenium per gram of tissue than almost any other organ. Selenium-dependent enzymes are responsible for converting your thyroid’s main hormone output into its active form, the version your cells actually use. Without adequate selenium, this conversion slows down, which can affect everything from your metabolism to your energy levels.
Selenium also plays a central role in your antioxidant defense system. Certain selenium-containing proteins neutralize hydrogen peroxide and other reactive molecules that accumulate during normal cell processes. These same protective enzymes are especially active in the thyroid, where hormone production generates a significant amount of oxidative byproducts.
Selenium and Immune Function
Your immune cells depend on selenium to function properly. When selenium is low, immune cells experience higher levels of oxidative stress, which impairs their ability to multiply and respond to threats. T cells, a key part of your adaptive immune system, show measurably reduced ability to proliferate when selenium is deficient. In animal studies, increasing selenium intake boosted the expression of surface receptors on immune cells that are necessary for activation, and restored their capacity to multiply in response to infection signals.
What Happens When You Get Too Little
Mild selenium deficiency often produces no obvious symptoms, which is part of what makes it tricky. The effects tend to show up as worsened outcomes from other health stresses rather than a distinct illness on their own. Over time, inadequate selenium can weaken immune responses, impair thyroid function, and reduce your body’s ability to manage oxidative damage.
Severe, prolonged deficiency is linked to a condition called Keshan disease, a form of heart muscle damage historically found in regions of China with extremely selenium-poor soil. The disease can range from subtle cardiac abnormalities detectable only on an EKG to acute heart failure with cardiogenic shock. It remains rare outside of specific geographic areas and is largely preventable with adequate selenium intake.
Signs You’re Getting Too Much
Selenium toxicity, sometimes called selenosis, is more likely to come from high-dose supplements or excessive Brazil nut consumption than from a normal diet. The earliest and most recognizable signs are brittle nails and hair loss, which is the basis for the 400-microgram upper limit. A metallic or garlic-like taste in the mouth (or garlic-scented breath, even without eating garlic) is another classic indicator. At higher doses, nausea, diarrhea, skin rashes, and fatigue can develop. In documented cases of people accidentally eating selenium-rich nuts in large quantities, nausea and vomiting appeared within hours, while hair loss and nail changes followed weeks later.