Selenium is an essential trace mineral found in soil, water, and some foods. It is an important factor in many body processes.

Selenium increases antioxidant effects in the body. Crab, fish, poultry, and wheat are generally good food sources. The amount of selenium in soil varies, and foods grown in different soils have different selenium levels. The Eastern Coastal Plain and Pacific Northwest have the lowest selenium levels in the US.

People commonly use selenium for selenium deficiency and to reduce the risk for high blood pressure during pregnancy. It is also used for prostate cancer, complications from statin drugs, abnormal cholesterol levels, cataracts, and many other conditions.