Selenium is a trace element that is naturally present in many foods. Selenium, which is nutritionally essential for humans, is a constituent of more than two dozen selenoproteins that play critical roles in reproduction, thyroid hormone metabolism, DNA synthesis, and protection from oxidative damage and infection.
Selenium exists in two forms: inorganic (selenate and selenite) and organic (selenomethionine and selenocysteine). Both forms can be good dietary sources of selenium.
Most selenium that is present in human tissues is in the form of selenomethionine where it can be incorporated non-specifically with the amino acid methionine in body proteins. Skeletal muscle is the major site of selenium storage, accounting for approximately 28% to 46% of the total selenium pool.
Because of seleniums’ effects on DNA repair, apoptosis, and the endocrine and immune systems as well as other mechanisms, including its antioxidant properties, selenium might play a role in the prevention of cancer. Selenium also supports the immune system by scavenging oxidative products that are produced during an immune response when invading viruses are attacked.
In addition, selenoproteins help prevent the oxidative modification of lipids, reducing inflammation and preventing platelets from aggregating. As a consequence, selenium could reduce the risk for cardiovascular diseases. Some studies have suggested that selenium may prevent the cognitive decline in elderly.
The European Food Safety Authority (EFSA) has acknowledged the following beneficial effects as a basis for health claims:
• Selenium contributes to normal thyroid function
• Selenium contributes to normal function of the immune system
• Selenium contributes to the protection of DNA, proteins and lipids from oxidative damage
• Selenium contributes to the maintenance of normal nails
• Selenium contributes to the maintenance of normal hair
• Selenium contributes to normal spermatogenesis