Selenium – Uses, Benefits, Sources and Dosage Selenium is a trace mineral which is found in soil, certain foods and also available in the small amount in water. It is also a crucial mineral for our body. Selenium acts as antioxidant when it combines with vitamin E. Antioxidants fight against the free radicals which may result in the damage of DNA and cell membrane. These free radicals are responsible for ageing and other health complications like cancer and heart diseases.