Selenium is an essential trace mineral. Small amounts of selenium are good for your health.

Selenium has a variety of functions. It helps make special proteins, called antioxidant enzymes, which play a role in preventing cell damage. Some medical information suggests that selenium may help prevent certain cancers, but better studies are needed.

There have also been mixed results regarding selenium's impact on cardiovascular disease.

Selenium seems to stimulate antibodies after you receive a vaccination. It also may help protect the body from the poisonous effects of heavy metals and other harmful substances.

Selenium may boost fertility, especially among men. The mineral has been shown to improve the production of sperm and sperm movement.

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

Fish, shellfish, red meat, grains, eggs, chicken, liver, and garlic are all good sources of selenium. 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.

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

Keshan disease is caused by a deficiency 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 selenium supplements were provided.

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 mental retardation

Severe gastrointestinal disorders may also affect the body's ability to absorb selenium.

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