Selenium is a trace mineral that the human body requires for proper functioning. It is obtained primarily through diet, playing a part in various biological processes. Organic selenium refers to forms of this mineral found naturally in living organisms, where it becomes incorporated into proteins. Its chemical structure influences how the body absorbs and uses it, making understanding organic selenium beneficial for health.
Differentiating Organic and Inorganic Selenium
The distinction between organic and inorganic selenium lies in their chemical composition. Inorganic selenium forms, such as selenite and selenate, are typically found in soil and water. Plants absorb these inorganic forms and convert them into organic compounds, primarily by incorporating selenium into amino acids like selenomethionine and selenocysteine. This process transforms the mineral into a form that living organisms can more readily utilize.
Organic selenium compounds are characterized by selenium being bound to a carbon-containing molecule, often an amino acid. Selenomethionine, for instance, is a common organic form found in foods and supplements, where selenium replaces the sulfur atom in methionine. This structural difference significantly impacts how the body handles the mineral. Organic forms like selenomethionine are absorbed more efficiently and retained longer in the body compared to inorganic forms, allowing for more effective utilization and storage within bodily tissues.
Natural Sources of Organic Selenium
Many natural foods provide organic selenium, with concentrations varying based on the soil selenium content where they are grown. Brazil nuts are notably rich in selenium, with a single nut often providing more than the daily recommended amount. Eating just a few Brazil nuts per week can significantly contribute to selenium intake.
Seafood, including various types of fish like tuna, halibut, and sardines, along with crustaceans such as crab, offers another substantial source of selenium. Organ meats, such as kidney, and muscle meats like beef, turkey, and chicken also contribute moderate amounts of this mineral. Eggs, particularly egg yolks, are reliable sources of selenium as well. Additionally, some whole grains and cereals contain selenium, and their widespread consumption makes them important daily contributors to overall intake.
The Role of Selenium in the Body
Selenium performs its functions within the body by becoming a component of specialized proteins called selenoproteins. These selenoproteins are involved in various biological activities, including redox reactions and inflammatory responses. One of selenium’s primary roles is in antioxidant defense, where it is a component of the enzyme glutathione peroxidase (GPx). This enzyme helps protect cells from damage caused by unstable molecules known as free radicals, which are byproducts of normal metabolic processes.
Selenium also supports thyroid hormone metabolism, which is a process that regulates growth, metabolism, and body temperature. The thyroid gland contains a higher concentration of selenium than any other organ, and selenoproteins are necessary for converting the inactive thyroid hormone T4 into its active form, T3. Selenium also contributes to immune system function. It influences the activity and proliferation of various immune cells, including natural killer cells, macrophages, and T cells, supporting the body’s defenses against infections.
Recommended Intake and Toxicity
The Recommended Dietary Allowance (RDA) for selenium in adults is 55 micrograms (µg) per day. This intake level is sufficient for most healthy individuals. While selenium deficiency is uncommon in some regions, such as the United States, it can occur in areas with low soil selenium content.
The Tolerable Upper Intake Level (UL) for selenium in adults is set at 400 µg per day. Consuming amounts above this UL can lead to selenium toxicity, a condition known as selenosis. Symptoms of selenosis may include a garlic-like odor on the breath, a metallic taste in the mouth, hair loss, brittle or deformed nails, gastrointestinal disturbances (like nausea or diarrhea), fatigue, irritability, and skin rashes. While toxicity from food sources is rare, it is possible with extreme consumption of very high-selenium foods like Brazil nuts or through excessive supplementation. In severe cases, selenosis can result in serious health issues, including nerve damage.