Medically Reviewed by Jabeen Begum, MD on August 21, 2023
5 min read

Selenium is a mineral found in the soil. It naturally appears in water and some foods. While people only need a very small amount, selenium plays a key role in their metabolism.

Selenium has attracted attention because of its antioxidant properties. Antioxidants protect cells from damage caused by things like aging, lifestyle choices, and environmental conditions like pollution. Over time, this cell damage – called oxidative stress – is linked to cancer, heart disease, and the decline of mental skills.

Selenium supports many of your body's functions, including:

  • Thyroid health. Your thyroid is a small gland that produces hormones to regulate your body’s metabolic processes. If you have an underactive thyroid, you may have fatigue, weight gain, depression, and muscle aches. Over time, thyroid risks can worsen chronic diseases.

    Selenium helps maintain healthy thyroid function. Research shows, though, that too much can harm your thyroid. 

  • Cognitive support. Research shows selenium’s antioxidant properties fight cell damage that may worsen brain and nervous system diseases like Parkinson’s, Alzheimer’s, and multiple sclerosis. Studies are ongoing to determine if selenium can help prevent or treat the loss of mental skills. But scientists believe getting enough in your diet can help maintain healthy brain function.

Selenium has also been studied for the treatment of dozens of other conditions. They range from asthma to arthritis to prostate cancer to infertility. The results of these studies have been inconclusive. 

The recommended dietary allowance (RDA) includes the total amount of selenium you should get from foods and from any supplements you take. Most people can get their RDA of selenium from food.

The safe upper limit for selenium is 400 micrograms a day in adults. Anything above that is considered an overdose.

Recommended Dietary Allowance
Children 1-320 micrograms/day
Children 4-830 micrograms/day
Children 9-1340 micrograms/day
Adults and children 14 and up55 micrograms/day
During pregnancy60 micrograms/day
While breastfeeding70 micrograms/day

The amount of selenium in a food largely depends on the soil conditions where that food was grown.

Good food sources of selenium include:

1. Brazil nuts

Brazil nuts are the most powerful source of selenium available. But it’s important to moderate your portions. Just one nut contains 95 micrograms, almost twice your daily requirement. Doctors advise taking no more than 400 micrograms of selenium a day to avoid potential health risks.

2. Seafood

Most seafood contains high levels of selenium. In a 3-ounce serving, yellowfin tuna and white fish like halibut have about 92 micrograms of the mineral, while tinned sardines contain 45 micrograms for the same portion. 

3. Lean meat

Meat is an excellent source of many essential nutrients, including selenium. A sautéed chicken breast can have up to 35 micrograms of selenium, with an extra 5 micrograms if you eat the skin. Lean varieties of beef can be a great choice as well. Serve up a 4-ounce portion of skirt steak to get 26 micrograms of selenium. 

4. Pasta

Pasta is an easy way to include selenium in most diets. One cup of cooked pasta has 36 micrograms, while whole-grain varieties have as much as 50 micrograms. 

5. Rice

Because most rice is gluten-free, it can be a good option for people with wheat allergies or celiac disease. One cup of cooked white rice contains 9 micrograms of selenium. But you can get about 15 micrograms from a cup of brown rice varieties. 

6. Eggs

One large egg can meet about 28% of your daily selenium requirement. Most is found in the egg’s yolk. If you're watching your cholesterol intake, the egg white also has about 9 micrograms of selenium. 

7. Oatmeal

Whether you have a bowl for breakfast, use it to thicken smoothies, or substitute it for flour in baked goods, oatmeal is an excellent selenium source. A cup of instant oatmeal contains 10 micrograms of selenium, while raw oats have up to 23 micrograms. 

8. Baked beans

Baked beans – including vegetarian products – contain about 12 micrograms of selenium per cup. Beans are a great source of fiber as well, but canned beans contain high amounts of sodium. Moderate your portions to avoid health risks that can come with a high-sodium diet.

Our bodies need selenium to work well, but there are risks to adding more to your diet, including:

  1. Side effects. Taken at normal doses, selenium doesn't usually have side effects. An overdose of selenium may cause bad breath, hair loss, fever, tiredness, and nausea.
  2. Interactions. Selenium may also interact with other medicines and supplements you take, such as some antacids, chemotherapy drugs, corticosteroids, niacin, cholesterol-lowering statin drugs, and birth control pills.
  3. Skin cancer. Selenium supplements may be linked to a risk of skin cancer (squamous cell carcinoma), so people at high risk of skin cancer shouldn't take these supplements.

Selenium toxicity

A little bit of selenium is usually plenty to meet your daily requirements. Over the long term, routinely getting unsafe levels could lead to selenium toxicity, a condition linked to  breathing issues, kidney failure, and heart problems. At high enough levels, selenium toxicity could even be fatal.

Among healthy people in the U.S., selenium deficiencies are rare. But some health conditions – such as HIV or Crohn's disease – put you at higher risk for low selenium levels. People who are fed through an IV are also at risk for selenium deficiency. 

Symptoms of selenium deficiency include:

  • Headache
  • Nausea 
  • Confusion
  • Fatigue
  • Seizure
  • Coma

Having a selenium deficiency could lead to:

  • Infertility in men and those assigned at male birth
  • Keshan disease (a type of heart disease)
  • Kashin-Beck disease (a type of arthritis).

Selenium supplements

Your doctor may suggest you take a selenium supplement if you have a deficiency. 

These supplements usually come in the form of capsules or tablets. But whole foods are the best sources of selenium, as the mineral may be destroyed when it's processed. Unless your doctor tells you to take a supplement, get selenium from foods to avoid taking too much.