Selenium Benefits, Recommended Intake, and Foods High in Selenium
Most people in the United States get enough selenium from food, but questions about selenium benefits, selenium-rich foods, daily selenium intake, supplements, deficiency, and toxicity are becoming increasingly common.
This guide explains how much selenium you need, which foods contain the most selenium, what current research says about its health benefits, and why getting too much can be harmful.
Pregnancy: 60 mcg/day
Breastfeeding: 70 mcg/day
Adult Upper Limit: 400 mcg/day
Top Food Source: Brazil nuts
Main Functions: Thyroid hormone metabolism, antioxidant defense, DNA production, reproduction, and immune function
What Is Selenium?
Selenium is an essential trace mineral, meaning your body needs it but only in very small amounts.
Selenium becomes part of specialized proteins called selenoproteins. These proteins help regulate several important processes, including thyroid hormone metabolism and antioxidant activity.
According to the National Institutes of Health, selenium is needed for normal thyroid function, DNA production, reproduction, cellular protection, and resistance to infection.
What Are the Main Selenium Benefits?
Selenium is essential for health, but it is important to distinguish between getting enough selenium and taking high-dose selenium supplements.
Meeting your nutritional needs supports normal body functions. Taking more than you need does not necessarily provide additional benefits.
1. Supports Antioxidant Defense
Selenium is a component of several antioxidant enzymes, including glutathione peroxidases.
These enzymes help protect cells from oxidative damage caused by reactive oxygen species and normal metabolic processes.
This does not mean selenium works as a stand-alone "anti-aging" or disease-prevention treatment. Its role is primarily to support normal antioxidant systems in the body.
2. Supports Healthy Thyroid Function
The thyroid contains a relatively high concentration of selenium.
Selenium-dependent enzymes are involved in the conversion of thyroxine (T4) into the more active thyroid hormone triiodothyronine (T3).
Selenium also helps protect thyroid tissue from oxidative stress.
Selenium is essential for thyroid health, but taking a selenium supplement is not automatically beneficial for everyone with thyroid disease. Research on supplementation remains mixed and depends partly on selenium status and the specific thyroid condition.
Recent systematic reviews of Hashimoto's thyroiditis have found that selenium supplementation may reduce certain thyroid antibodies and may modestly affect TSH in some patients, but evidence is not strong enough to treat selenium as a replacement for standard thyroid care.
3. Helps Support Normal Immune Function
Selenium contributes to both innate and adaptive immune function.
Adequate selenium status supports normal activity of immune cells, including T cells and natural killer cells.
However, this should not be interpreted as meaning that high-dose selenium supplements will prevent colds, flu, COVID-19, or other infections.
4. Supports DNA Production and Reproduction
Selenium plays a role in DNA synthesis and reproductive health.
It is also involved in normal sperm development. Although selenium is important for male fertility, current evidence does not clearly show that selenium supplements improve fertility in people who already get enough from their diet.
Does Selenium Prevent Cancer?
This is one of the most misunderstood selenium claims.
Observational studies have sometimes found associations between adequate selenium status and lower rates of certain cancers. However, randomized clinical trials have not shown that selenium supplements reliably prevent cancer.
NIH notes that selenium supplementation has not been shown to reduce prostate cancer risk, particularly in people who already consume adequate selenium.
Selenium is an essential nutrient, but selenium supplements should not be used as a cancer-prevention strategy.
Does Selenium Protect the Heart?
Selenium's antioxidant role led researchers to study whether supplements might prevent cardiovascular disease.
Current evidence does not show that selenium supplements reliably reduce the risk of heart disease in people who already get adequate selenium.
A healthy dietary pattern, exercise, blood-pressure management, cholesterol control, and avoiding tobacco remain much more important for cardiovascular health.
How Much Selenium Do You Need Per Day?
According to the NIH Office of Dietary Supplements, the recommended daily selenium intake varies by age and life stage.
| Age / Life Stage | Recommended Selenium Intake |
|---|---|
| Birth to 6 months | 15 mcg/day |
| 7–12 months | 20 mcg/day |
| Children 1–3 years | 20 mcg/day |
| Children 4–8 years | 30 mcg/day |
| Children 9–13 years | 40 mcg/day |
| Teens 14–18 years | 55 mcg/day |
| Adults | 55 mcg/day |
| Pregnant teens and women | 60 mcg/day |
| Breastfeeding teens and women | 70 mcg/day |
Foods High in Selenium
Most people can meet their selenium needs through food.
Good sources include:
- Brazil nuts
- Tuna and other seafood
- Sardines
- Shrimp
- Beef
- Pork
- Chicken and turkey
- Eggs
- Dairy products
- Breads and cereals
- Beans and lentils
The selenium content of plant foods can vary substantially because selenium levels depend partly on the soil in which the food was grown.
Are Brazil Nuts High in Selenium?
Yes. Brazil nuts are one of the most concentrated natural sources of selenium.
According to NIH, one Brazil nut can contain approximately 68–91 mcg of selenium.
One Brazil nut: about 68–91 mcg
This means a single Brazil nut can provide more than the adult daily requirement.
Because selenium content varies, eating multiple Brazil nuts every day can push total intake unnecessarily high.
What Is Selenium Deficiency?
Selenium deficiency is rare in the United States and Canada.
Most Americans get enough selenium through food. However, low selenium status is more likely in certain groups.
Who May Be at Higher Risk?
- People undergoing kidney dialysis
- People living with HIV
- People whose diets depend heavily on foods grown in selenium-poor soils
Severe selenium deficiency can worsen iodine deficiency and can contribute to certain rare diseases, including Keshan disease and Kashin-Beck disease.
What Are Selenium Deficiency Symptoms?
Mild selenium deficiency usually does not produce a simple, specific set of symptoms that can be diagnosed at home.
Because symptoms such as fatigue, weakness, hair changes, or thyroid problems can have many causes, they should not automatically be attributed to low selenium.
If deficiency is suspected, a healthcare professional can evaluate diet, medical conditions, medications, and appropriate laboratory testing.
Should You Take a Selenium Supplement?
For most healthy people in the United States, a selenium supplement is usually unnecessary because dietary intake is typically adequate.
Selenium supplements may contain forms such as:
- selenomethionine,
- selenium-enriched yeast,
- sodium selenite,
- and sodium selenate.
Before adding a supplement, check how much selenium you already receive from:
- food,
- multivitamins,
- individual mineral supplements,
- and fortified products.
Look at the Supplement Facts label. Some multivitamins already contain the full adult RDA of selenium, so adding another selenium-only product may be unnecessary.
How Much Selenium Is Too Much?
For U.S. adults, the NIH lists a tolerable upper intake level of 400 mcg per day from food, beverages, and supplements combined.
Adult Upper Limit: 400 mcg/day
The upper limit is not a recommended target. It is the highest average daily intake that is unlikely to pose risk for most people.
Selenium Toxicity Symptoms
Long-term excessive selenium intake can cause selenosis.
Possible symptoms include:
- Garlic-like breath odor
- Metallic taste
- Hair loss
- Brittle nails or nail loss
- Skin rash
- Nausea
- Diarrhea
- Extreme fatigue
- Irritability
- Nervous system problems
Very high selenium exposure can cause severe gastrointestinal and neurological symptoms and, in extreme cases, serious kidney or heart complications.
Can You Get Too Much Selenium From Brazil Nuts?
Yes.
Because a single Brazil nut may contain 68–91 mcg, eating several every day can quickly raise your intake.
For example, five Brazil nuts could theoretically provide roughly 340–455 mcg, depending on their selenium content.
That could approach or exceed the U.S. adult upper limit before accounting for selenium from other foods or supplements.
Selenium and Thyroid Health
Selenium has one of its clearest biological roles in the thyroid.
Selenium-containing enzymes help:
- convert T4 into T3,
- regulate thyroid hormone metabolism,
- and protect thyroid cells from oxidative stress.
Recent research in people with Hashimoto's thyroiditis suggests selenium supplementation may lower certain thyroid antibodies and modestly change some laboratory markers in selected patients. However, results are not consistent enough to recommend routine self-treatment.
Anyone with hypothyroidism, Hashimoto's disease, Graves' disease, or other thyroid conditions should discuss selenium supplements with a clinician.
Selenium and the Immune System
Selenium contributes to normal immune-cell development and activity.
People with selenium deficiency may have impaired immune responses, but that does not mean extra selenium above nutritional requirements will make the immune system "stronger."
The goal should be adequate intake, not megadosing.
Selenium FAQ
How much selenium should I take daily?
Most adults need 55 mcg per day. Pregnant women need 60 mcg, and breastfeeding women need 70 mcg.
What food has the most selenium?
Brazil nuts are among the richest natural sources. One nut can contain approximately 68–91 mcg, although the amount varies.
Can I eat Brazil nuts every day?
Small amounts may fit into a healthy diet, but regular consumption of several Brazil nuts per day can lead to excessive selenium intake.
Is selenium good for your thyroid?
Yes, selenium is essential for normal thyroid hormone metabolism. However, selenium supplements are not automatically beneficial for everyone with thyroid disease.
Does selenium prevent cancer?
Current clinical evidence does not support using selenium supplements as a reliable method of cancer prevention.
Does selenium boost immunity?
Selenium is required for normal immune function, but taking more than your body needs has not been shown to create a generally "stronger" immune system.
Is 200 mcg of selenium too much?
Two hundred micrograms is below the U.S. adult upper limit of 400 mcg, but it is more than three times the adult RDA of 55 mcg. For someone who already gets enough selenium from food, routine supplementation at that level may be unnecessary.
What happens if you take too much selenium?
Excessive selenium can cause garlic breath, metallic taste, nausea, diarrhea, hair loss, brittle nails, fatigue, irritability, and nervous system symptoms.
Bottom Line: Do You Need More Selenium?
Selenium is essential, but more is not necessarily better.
For most Americans, a balanced diet containing seafood, meat, poultry, eggs, dairy, whole grains, legumes, and nuts provides enough selenium without supplementation.
Adults: 55 mcg/day
Pregnancy: 60 mcg/day
Breastfeeding: 70 mcg/day
Adult Upper Limit: 400 mcg/day
If you are considering a selenium supplement, especially for a thyroid condition, fertility concern, or other medical reason, talk with a qualified healthcare professional before taking high doses.
Trusted Selenium Resources
NIH Selenium Fact Sheet USDA FoodData Central
This article is for educational and informational purposes only and is not a substitute for medical advice, diagnosis, or treatment. Nutrient needs can vary based on health conditions, medications, pregnancy, and other factors. Talk with a healthcare professional before taking high-dose selenium supplements.
