- Selenium is an essential trace mineral found in soil, water, and some foods. It is a component of the amino acids cysteine and methionine. Selenium is required for functioning of the body's antioxidant enzymes and for cell growth and survival.
- The presence of selenium in locally grown food and selenium levels in human populations reflects the selenium levels in local soil. The selenium content in food is influenced by geographical location, seasonal changes, protein content, and food processing. Periodic monitoring of selenium levels in soil and food is necessary. Selenium supplements may benefit people living in regions with very low environmental levels of selenium.
- Selenium has a strong protective action against the poisonous effects of many heavy metals, some toxic compounds, and fungal toxins.
- The role of selenium in cancer prevention has been the subject of recent study and debate. Initial evidence from the Nutritional Prevention of Cancer (NPC) trial suggested that selenium supplementation reduced the risk of prostate cancer among men with normal baseline PSA (prostate specific antigen) levels and low selenium blood levels. However, in this study, selenium did not reduce the risk of lung, colorectal, or basal cell carcinoma of the skin and actually increased the risk of squamous cell skin carcinoma.