Selenium: Overview, Benefits, and Food Sources

What is selenium?

Selenium is a natural mineral found in soil and foods that some people take as a dietary supplement. It is an essential trace mineral — meaning your body needs it to function, but only in small amounts.  

Selenium is necessary to make proteins that help cells in your body function properly. It is also an important antioxidant. This means that selenium is helpful in repairing any damaged cells in the body. Selenium also has an especially important role in thyroid function and the metabolism of thyroid hormone.

People often use selenium as a supplement if they have selenium deficiency (lower than normal levels of selenium). This occurs in regions where selenium content in the soil is low, causing low dietary intake. You can also take selenium if your body doesn’t absorb it well due to certain health conditions.

Selenium: Sources and supplements

You can get selenium in your diet from both plant-based and animal-based foods. Common food sources of selenium include: 

• Nuts (Brazil nuts, cashews)

• Seafood (tuna, halibut, sardines, shrimp)

• Meats (ham, steak, turkey, chicken, beef liver)

• Grains (pasta, lentils, breads, oatmeal) 

• Dairy products (milk, cottage cheese, yogurt)

• Eggs

The amount of selenium in both plant-based and animal-based foods will vary. How much selenium you get from your food depends on the farm soil where your food comes from. There is often no clear way to know how much selenium is in the food you are eating. Still, most people in the U.S. get adequate amounts of selenium in their diets. 

In some cases, it is difficult to get enough selenium from your diet alone. Conditions such as Crohn’s disease, weight loss surgery, and other serious gastrointestinal illnesses may make it harder to absorb nutrients like selenium from your diet. 

For those who are at risk of selenium deficiency, supplements are an option. 

Selenium supplements come in two forms, selenomethionine or sodium selenate. Selenomethionine is more widely used as a pure selenium supplement, and sodium selenate is in many multivitamins. 

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Selenium is available over the counter as:

• Capsules (100 mcg to 200 mcg capsules)

• Tablets (50 mcg to 200 mcg tablets)

• Oral liquid 

It is also available as an intravenous (IV) solution when prescribed for selenium deficiency.

Another type of selenium is selenium sulfide. This form is available as a medicated lotion and shampoo that treats minor skin conditions like dandruff. But selenium sulfide is different from selenium dietary supplements. Selenium applied to the skin will not affect blood levels of selenium.

Selenium supplement dosing

The recommended amount of selenium your body needs each day increases with age. The daily recommendations are as follows:

Children

• 1 to 3 years old: 20 mcg

• 4 to 8 years old: 30 mcg

• 9 to 13 years old: 40 mcg

• 14 to 17 years old: 55 mcg

Adults

• 18 years old and up: 55 mcg

• Pregnant people: 60 mcg

• Nursing people: 70 mcg  

On average, most people get more than 100 mcg of selenium from their diets each day, so they don’t need selenium supplements. If you have a condition that puts you at risk for not meeting the daily allowance of selenium, supplements may be necessary. 

Is it safe to take selenium every day?

It depends. Taking selenium each day if you don’t have a deficiency could lead to higher than normal levels. The recommended limit for adults is 400 mcg per day from both diet and supplement sources. 

Common uses for selenium supplements

People with low levels of selenium may use selenium as a supplement. In these people, selenium supplements may prevent or treat complications such as muscle disorders, thyroid disorders, heart disease, and immune dysfunction. 

What are the symptoms of selenium deficiency?

Symptoms of selenium deficiency can vary based on severity but may include:

• Achy bones and joints

• Muscle pain

• Fatigue

• Heart rhythm abnormalities

• Signs of heart failure

• Depressed mood

Selenium deficiency is not common. The only way to know if you have low selenium levels is to get a blood test. You are more likely to have a selenium deficiency if you have:

• A diet low in selenium (not common in the U.S.)

• Chronic diarrhea

• Gastrointestinal surgeries or disorders that can affect absorption

• Inflammatory bowel disease, like Crohn’s disease

• Intravenous (IV) nutrition

• HIV

• Kidney failure with dialysis

The science behind selenium

Taking selenium supplements is helpful only in people with low levels of selenium. There is not enough evidence to suggest that there is any added health benefit in those with normal selenium levels. 

While people with dementia tend to have low levels of selenium, supplements do not help prevent dementia. 

Selenium also has antioxidant properties that researchers tested for help in cancer prevention. But there is no clear evidence to support selenium supplements as useful in preventing cancer. 

Selenium supplement interactions

Selenium may interact with some medications and make them more or less effective. 

Medications that may be more potent or longer lasting if you take them with selenium include:

• Aspirin

• Clopidogrel (Plavix)

• Warfarin (Coumadin)

• Certain sedative medications, such as barbiturates 

Medications that may be less effective if you take them with selenium include certain cholesterol medications, such as simvastatin (Zocor).

On the other hand, some medications may lower your levels of selenium. These include:

• Certain cancer medications, such as cisplatin

• Clozapine

Selenium supplement side effects

Selenium supplements don’t have too many side effects when taken as directed. People who take more selenium than is recommended may experience side effects such as:

• Garlic-smelling breath

• Brittle hair or nails

• Hair or nail loss

• Changes in teeth color

• Sleepiness

• Feeling more irritable than normal

• Skin rashes

• Nausea

• Diarrhea

Safety of selenium supplements

Most people can safely take selenium supplements, including people who are pregnant or nursing. 

Some people should use caution with selenium supplements, such as people with kidney problems or severe gastrointestinal (GI) issues. 

Disclaimer: The FDA does not test supplements for safety and effectiveness. Supplements can contain harmful substances. They can also affect how your medications work. Always speak with your healthcare provider before taking any supplement.

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Written by:

Karla Robinson, MD

Karla Robinson, MD, is a medical editor for GoodRx. She is a licensed, board-certified family physician with almost 20 years of experience in health through varied clinical, administrative, and educational roles.

Reviewed by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

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