Selenium is a trace element. Your body only needs it in small amounts.

Selenium helps your body make special proteins, called antioxidant enzymes. These play a role in preventing cell damage.

Some research suggests that selenium may help with the following:

• Prevent certain cancers
• Protect the body from the poisonous effects of heavy metals and other harmful substances

More studies on the benefits of selenium are needed. Taking a selenium supplement in addition to food sources of selenium is not currently recommended for these conditions.

Plant foods, such as vegetables, are the most common food sources of selenium. How much selenium is in the vegetables you eat depends on how much of the mineral was in the soil where the plants grew.

Brazil nuts are a very good source of selenium. Fish, shellfish, red meat, grains, eggs, chicken, liver, and garlic are also good sources. Meats produced from animals that ate grains or plants found in selenium-rich soil have higher levels of selenium.

Brewer's yeast, wheat germ, and enriched breads are also good sources of selenium.

Lack of selenium is rare in people in the United States. However, deficiency may occur when a person is fed through a vein (IV line) for long periods of time.

Keshan disease is caused by a lack of selenium. This leads to an abnormality of the heart muscle. Keshan disease caused many childhood deaths in China until the link to selenium was discovered and supplements were given.

Two other diseases have been linked to selenium deficiency:

• Kashin-Beck disease, which results in joint and bone disease
• Myxedematous endemic cretinism, which results in intellectual disability

Severe gastrointestinal disorders may affect the body's ability to absorb selenium. Such disorders include Crohn disease.

Too much selenium in the blood can cause a condition called selenosis. Selenosis can cause hair loss, nail problems, nausea, irritability, fatigue, and mild nerve damage. However, selenium toxicity is rare in the United States.

Dosages for selenium, as well as other nutrients, are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board at the National Academies of Sciences, Engineering, and Medicine. DRI is a term for a set of reference intakes that are used to plan and assess the nutrient intakes of healthy people.

How much of each vitamin you need depends on your age and sex. Other factors, such as pregnancy and illnesses, are also important. Women who are pregnant or breastfeeding need higher amounts. Ask your health care provider which amount is best for you. These values include:

• Recommended Dietary Allowance (RDA): The average daily level of intake that is enough to meet the nutrient needs of nearly all (97% to 98%) healthy people. An RDA is an intake level based on scientific research evidence.
• Adequate Intake (AI): This level is established when there is not enough scientific research evidence to develop an RDA. It is set at a level that is thought to ensure enough nutrition.

Dietary Reference Intakes for selenium:

Infants (AI)

• 0 to 6 months: 15 micrograms per day (mcg/day)
• 7 to 12 months: 20 mcg/day

Children (RDA)

• Age 1 to 3: 20 mcg/day
• Age 4 to 8: 30 mcg/day
• Age 9 to 13: 40 mcg/day

Adolescents and adults (RDA)

• Males, age 14 and older: 55 mcg/day
• Females, age 14 and older: 55 mcg/day
• Pregnant females: 60 mcg/day
• Lactating females: 70 mcg/day

The best way to get the daily requirement of essential vitamins is to eat a balanced diet that contains a variety of foods.

Markell M, Siddiqi HA. Vitamins and trace elements. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 27.

Mason JB, Booth SL. Vitamins, trace minerals, and other micronutrients. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 205.

National Institutes of Health website. Selenium: fact sheet for health professionals. ods.od.nih.gov/factsheets/Selenium-HealthProfessional/. Updated March 26, 2021. Accessed February 9, 2023.

Updated by: Stefania Manetti, RD/N, CDCES, RYT200, My Vita Sana LLC - Nourish and heal through food, San Jose, CA. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.