Selenomethionine is an amino acid that contains selenium. It exists in two forms known as enantiomers, including L-selenomethionine and D-selenomethionine. L-selenomethionine is biologically active in humans and many other life forms.

The primary value of L-selenomethionine in health supplements is to provide a bioavailable form of selenium, which is an essential human nutrient. L-selenomethionine may be easier to absorb than selenite, which is an inorganic form of selenium commonly used in health supplements. One clinical trial showed that L-selenomethionine has an absorption rate 19 percent higher than that of selenite.

Selenium plays an essential role in many biochemical reactions, especially as a cofactor for reducing antioxidant enzymes. L-selenomethionine oxides readily, allowing it to reduce the level of reactive oxygen compounds. These compounds include free radicals, which can cause cellular damage.

The best dietary sources of selenium include cereal grains, legumes and soybeans, with Brazil nuts typically having the highest level of selenium. However, the selenium content of plants generally depends more on the amount of selenium in the soil than the species of plant. Additional sources of selenium include fish, crustaceans, organ meats, mushrooms and eggs. The adult human body contains up to 20 milligrams (mg) of selenium, and the minimum daily requirement of selenium for adults is at least 55 micrograms (mcg) per day.

Uses of L-Selenomethionine

As a source of selenium, L-selenomethionine has many specific uses. The most common reasons for taking L-selenomethionine in a health supplement include support for the thyroid gland, heart, immune system and management of healthy cholesterol levels.

Signs You May Need L-Selenomethionine

The relatively high abundance of selenium in the soil and its low nutritional requirement means that a selenium deficiency is rare in humans. This is most likely in patients with severely compromised gastrointestinal function, which may occur after gastrointestinal bypass surgery or in very elderly patients. The most common signs that you may need L-selenomethionine include poor heart function and degeneration of cartilage. General fatigue and a weak immune system may also mean that you may benefit from L-selenomethionine.