Selenium: The Overlooked Mineral That Helps Your Body Handle Heavy Metals and Microplastics (2026 Update)

Heidi Moretti, MS, RD, CLT — registered dietitian with 25+ years of clinical experience in functional nutrition, and author of Cortisol Fix. This article is medically reviewed for accuracy and updated with 2025–2026 research.

Of all the essential nutrients, selenium is exceptionally important but also exceptionally misunderstood. The reason it’s misunderstood is that there are many factors dictating how much selenium your body actually gets from any given food, and what happens to it once it’s inside you.

Here are some of the main reasons selenium is confusing:

• The amount of selenium in soil largely dictates how much selenium ends up in your food
• Selenium content of the soil varies wildly from place to place
• There is a relatively narrow range of ideal intake for selenium
• Selenium absorption varies a lot from person to person
• The amount of selenium that’s ideal for a person can change over time
• Selenium can be depleted by medications and medical procedures

Despite all of this confusion, selenium is a mineral that is more often lacking than not in people’s diets — and with rising concerns about heavy metal and microplastic exposure, it’s become more relevant to me clinically than it’s ever been.

In this article, learn all of the benefits of selenium, its risks, the best selenium-rich foods, absorption considerations, and why I personally eat Brazil nuts every single day.

What Does Selenium Do?

Selenium is a trace mineral that performs many functions in the body. As an antioxidant that fights oxidative stress, selenium is protective against oxidative stress, which reduces the risk of many chronic diseases like cancer and heart disease. It may even support metabolism by increasing the number of mitochondria in our cells.

Our very own DNA relies on selenium to be made. Selenium is also essential for making thyroid hormones that support metabolism. As an antioxidant, selenium helps proper immune function and supports healthy fertility, especially in men.

This mineral is also necessary for healthy brain function. As you can imagine, selenium is critical for the health of every cell in the body.

The Many Benefits of Selenium

As an essential mineral and antioxidant, selenium is important for every cell in the body. Some of its essential roles include proper metabolism, thyroid function, immune function, and more.

Specific Antioxidant Roles

Selenium helps neutralize free radicals that damage thyroid hormone production and prevents cellular damage from oxidation in general. DNA repair: Selenium is involved in DNA repair mechanisms tied to cancer and heart disease risk.

Helps Thyroid Function

Because of its antioxidant abilities, selenium can also reduce thyroid antibodies in autoimmune thyroid disorders like Graves’ disease and Hashimoto’s thyroiditis. It helps neutralize excess iodine too. Selenium also plays a role in converting thyroid hormone into its active T3 form.

Helps Brain Function

By neutralizing toxins and reducing oxidative stress, selenium helps brain function in many ways. Impressively, a review of 6 clinical studies on selenium and cognitive decline showed selenium does indeed improve memory and cognitive function in people with Alzheimer’s disease and mild cognitive impairment.

Proper Immune Function

Selenium helps fight infection by making the immune system more responsive to pathogens and reduces inflammation — even in daunting conditions like tuberculosis, hepatitis C, and AIDS. Selenium is capable of reducing viral infection severity as well.

Cancer Risk Reduction

High dietary intake of selenium helps reduce the risk of stomach, colorectal, lung, breast, bladder, and prostate cancers. Supplementation of selenium reduces cancer mortality risk from skin cancer as well, though selenium combined with vitamin E has not been helpful for reducing prostate cancer mortality. Sadly, almost all cancer research measuring selenium has been conducted in men, not women.

Helps Heart Function

Higher selenium intake is related to a marked reduction in heart disease risk. Selenium also reduces the risk of heart failure and cardiomyopathies. A deficiency of selenium leads to a specific childhood heart disease called Keshan disease. When combined with coenzyme Q10, supplemental selenium reduces cardiovascular mortality in elderly people.

May Improve Lung Function

Selenium is related to improvements in lung function for people with asthma. Supplemental selenium also improved asthma symptoms in a small clinical trial.

Anti-Aging

By repairing DNA and reducing cellular senescence, selenium supplements protect skin stem cells from aging-related decline.

May Help People with Kidney Disease

A study in people with kidney disease and low selenium status examined whether supplemental selenium and coenzyme Q10 would improve kidney function. After 2 years, kidney function markers improved. In people with end-stage renal disease on hemodialysis, selenium supplements reduced DNA damage in white blood cells. Brazil nuts, rich in selenium, reduced inflammation in dialysis patients. Higher selenium intake is related to a reduced risk of kidney disease in population studies, though not all research agrees. The majority of research suggests selenium is protective for the kidney, but excess environmental selenium exposure should still be avoided.

May Reduce The Symptoms of Heavy Metal Toxicity

Selenium may help counteract toxic heavy metals like lead, mercury, and cadmium. It helps redistribute mercury to less sensitive organs; it binds to inorganic mercury and forms a stable, safer mercury-selenium complex; it reduces mercury absorption from the GI tract; and it helps restore a healthy antioxidant environment in the body.

A human study on plasma selenium and arsenic methylation capacity reinforces this further: higher plasma selenium was directly associated with more efficient arsenic methylation, converting toxic inorganic arsenic into far less harmful methylated forms that the body can excrete more easily — a separate pathway from its mercury-binding role.

Still, it’s important to reduce your exposure to common sources of heavy metals whenever possible.

Gut Health

Selenium positively affects gut colonization of healthy microbiome bacteria. The absorption and metabolism of dietary selenium may also be affected by your resident gut bacteria. Selenium may help protect against inflammatory bowel diseases, though more research is needed. Selenium also reduces intestinal permeability (leaky gut) by increasing tight junction protein expression and reducing oxidative stress.

Reproductive Health

Low selenium levels are related to pregnancy complications and miscarriage risk, as well as damage to the developing fetus’s nervous and immune systems and low birth weight. Selenium also helps increase sperm concentration and motility and reduces sperm DNA fragmentation in some men with infertility.

May Reduce Microplastic Harms

Microplastics are everywhere, and they are harmful to health. Certain nutrients and compounds like selenium may help reduce the cellular toxicity of ingested microplastics by improving mitochondrial function in cells. Selenium may also protect cells from the inflammation microplastics cause, and may even help prevent the liver damage they cause, called non-alcoholic fatty liver disease (NAFLD).

This isn’t a fringe concern anymore. A landmark 2025 Nature Medicine study on microplastics in human tissue found microplastics accumulating in human liver, kidney, and brain tissue — with brain concentrations higher than either organ, and roughly 50% higher in 2024 samples than in samples from 2016. The dominant polymer found was polyethylene, one of the most common plastics in food packaging. Separate 2025 research on the blood-brain barrier has since confirmed microplastics crossing into the central nervous system, and other recent studies have detected them in human blood, placenta, and testis tissue. None of this proves microplastics cause disease — but it does mean the body’s antioxidant and detoxification systems, selenium included, are working overtime compared to a generation ago.

Skin and Scalp Health

Topical selenium helps treat dandruff and skin fungal infections like candida.

Where Does Selenium Come From?

As a mineral, selenium is found in the soil and is especially concentrated in foods grown in selenium-rich soil.

Brazil nuts are commonly thought to be uniformly high in selenium, but this is only true if they’re grown in regions like the Amazon rainforest, where soil selenium content is naturally high. In contrast, Brazil nuts grown in New Zealand will have a low selenium content due to that region’s soil levels.

Even within Brazil, nuts can vary 10-fold in selenium content depending on the specific growing region. So the truth is, it’s genuinely difficult to know exactly how much selenium you’re getting from any single nut.

Simplified overview of selenium’s antioxidant and detoxification-support mechanisms discussed in this article.

Recommended Daily Intake of Selenium

The recommended daily intake (RDI) of selenium varies by age:

• Infants: 15 mcg
• Children: 20–40 mcg
• Adults: 55 mcg
• Pregnant women: 60 mcg
• Breastfeeding women: 70 mcg

Keep in mind the RDI wasn’t developed to optimize health — it doesn’t account for situations where you may need more selenium, such as digestive disorders, thyroid disorders, or heavy metal toxicity.

Selenium-Rich Foods and Considerations for Absorption

Selenium is found in two forms in food: organic and inorganic. Organic forms are more common in nuts and seeds, while inorganic selenium is mostly found in animal sources.

Brazil nuts are the primary source of selenium in many countries. Crab, liver, other shellfish, and fish provide moderate amounts, but their usefulness is limited because the inorganic selenium found in fish and meat is less well absorbed. Known contaminants like arsenic and mercury in fish can also reduce selenium’s effectiveness.

Here’s an overview of the selenium content of common foods, though keep in mind actual content varies dramatically by where a food is grown and what else may be reducing its absorption:

• Brazil nuts: one of the richest sources of selenium, with a single nut providing up to 91 mcg
• Fish: Tuna, canned salmon, and sardines can provide up to 45 mcg per 3-oz serving
• Eggs: A large egg provides up to 15 mcg
• Lean meats: Beef, chicken, lamb, venison, and pork, if raised on selenium-rich feed, provide up to 30 mcg per 3-oz serving
• Seafood: Shrimp, crab, and lobster can provide up to 40 mcg per 3-oz serving
• Beans: Kidney beans, black beans, and chickpeas can provide up to 10 mcg per cup
• Nuts and seeds: Sunflower seeds, pumpkin seeds, and chia seeds can provide up to 10 mcg per ounce
• Whole grains: Brown rice, quinoa, and whole wheat bread can provide up to 10 mcg per slice/serving
• Mushrooms: Shiitake and portobello mushrooms can provide up to 10 mcg per cup

How Many People Have Selenium Deficiency?

Selenium deficiency is quite common. Between 500 million and 1 billion people worldwide are estimated to be selenium deficient, mostly due to insufficient dietary intake.

Part of the reason deficiency is so common is that most dietary selenium is eliminated from the body within 24–48 hours. This is, in part, why people eating a very selenium-rich diet in Brazil, including frequent Brazil nut consumption, don’t typically show signs of selenium toxicity.

Soil selenium concentrations tend to be low in the U.S. Northwest, Northeast, Southeast, and parts of the Midwest near the Great Lakes. Many regions of the world are also naturally low in selenium, including parts of Europe, Africa, and China.

As climate patterns shift, selenium content in soil may also be decreasing — dry soil and poor soil health from modern agricultural practices are both associated with lower selenium levels.

People eating diet-related or highly processed Western diets are especially vulnerable to selenium deficiency. You’re also more likely to have selenium deficiency if you have a digestive condition like ulcerative colitis, celiac disease, Crohn’s disease, or another inflammatory bowel disease. Digestive tract surgeries also increase risk. And if you have vitamin E deficiency, your selenium deficiency is likely to be more severe.

What Happens if You Eat More Selenium than the RDI?

Higher selenium intake from food sources has the benefit of helping prevent heavy metal toxicity symptoms such as neurological issues and poor cognitive function.

Adding Brazil nuts at 5–10 nuts per day, three times per week, to an already selenium-rich diet in children increased blood selenium significantly, with no toxicity symptoms reported.

This all leads me to believe the risk of selenium toxicity from whole foods like Brazil nuts is a bit overblown in the media and in health textbooks. It’s conceivable that eating high-selenium foods is worth considering if you’re a regular fish eater, specifically to help offset mercury exposure.

According to WebMD, doctors recommend eating fewer than 5 Brazil nuts per day to avoid selenium toxicity. Healthline recommends just 1–3 per day. While I understand the caution, there are no published case reports of selenium toxicity directly linked to Brazil nut consumption at typical intakes.

Symptoms of Selenium Deficiency

As mentioned, selenium deficiency is common but rarely diagnosed, since conventional doctors seldom check selenium levels.

Heart muscle damage (cardiomyopathy) or congestive heart failure: Deficiency of selenium can even lead to sudden death, and can contribute to atherosclerosis.

Immune system compromise can result from insufficient selenium intake or poor absorption due to digestive disorders.

Fatigue, including muscle weakness and tenderness.

Infertility can result from selenium deficiency, as can miscarriage.

Mood changes: low selenium has been linked to depression and anxiety symptoms.

Memory loss: selenium deficiency can contribute to cognitive dysfunction.

Thyroid disorders: selenium is critical for proper thyroid hormone regulation, so abnormal thyroid levels and antibodies can relate to selenium status.

Selenium Toxicity

Selenium toxicity is possible but rare.

Acute selenium toxicity occurs when someone ingests a large amount of selenium in a short period. Symptoms can include nausea, vomiting, diarrhea, hair loss, and nail changes. This is rare and typically tied to environmental exposures, such as gun bluing agents, or large supplement doses.

Chronic selenium toxicity occurs with high selenium intake over a long period. Symptoms can include fatigue, GI problems, and neurological damage.

A review of acute toxicity cases found mortality associated with very large doses of 1–100 mg Se/kg body weight — nearly impossible to reach through supplements alone. A case series of 201 individuals who ingested a misformulated supplement containing 200 times the labeled selenium concentration reported diarrhea, fatigue, hair loss, joint pain, and nail discoloration — symptoms that slowly reversed for all affected. Reputable supplement brands with third-party testing make this kind of misformulation extremely unlikely today.

To avoid selenium toxicity, it’s generally best to get supplemental selenium as part of a multivitamin/mineral formula rather than as an isolated high-dose selenium supplement.

Types of Selenium Blood Tests

Knowing your selenium status can be genuinely useful for optimizing health. Most selenium in the body is stored in skeletal muscle, making up 28–46% of total body selenium.

• Whole blood selenium: reflects long-term selenium status
• Plasma selenium: reflects recent intake and daily fluctuations
• Erythrocyte selenium: reflects total body selenium stores via red blood cells

Normal Selenium Ranges

Normal ranges vary by lab and test type. Levels above these ranges can still be acceptable if you’re free of toxicity symptoms.

• Whole blood selenium: 0.5–2.5 μg/mL
• Plasma selenium: 0.1–0.5 μg/mL
• Erythrocyte selenium: 0.2–1.5 μg/mL

Do I Need a Selenium Supplement?

If you’re considering a selenium supplement, this is the most important question to answer first. Ideally, know your selenium levels before supplementing on its own — for most people, the amount of selenium in a well-formulated multivitamin/mineral combination is sufficient.

One study with strong evidence for selenium’s role in managing a thyroid-associated condition found that selenium supplementation considerably improved quality of life and slowed disease progression in patients with mild Graves’ eye disease, using a relatively modest 100 mcg/day dose.

While selenium deficiency may contribute to autoimmune thyroid conditions, excessively high intake carries its own risk of toxicity symptoms. Talk to your doctor or healthcare provider before making any supplement decisions.

Does the Form of Selenium Supplement Matter?

Selenium supplements come in two forms:

• Inorganic (selenate and selenite)
• Organic (selenomethionine and selenocysteine)

Organic forms have higher bioavailability and are better absorbed. Selenomethionine, in particular, is highly absorbable and has strong antioxidant properties. The body absorbs over 90% of selenomethionine, but only about 50% of selenium from selenite (the inorganic form).

Check the ingredient list of your multivitamin/mineral supplement to see which form of selenium it uses. For supplement quality, look for brands with third-party certifications from GMP-certified facilities, NSF, or USP. I generally recommend taking selenium as part of a multivitamin/mineral combination rather than alone, to avoid excess intake.

Frequently Asked Questions

This post is for informational purposes only and is not meant as medical advice. Talk to your doctor or healthcare provider before making any changes to your health regimen. Individual guidance should be based on your baseline health and judged by your own healthcare provider.