Description
Selenium is a trace mineral and a constituent of more than two dozen selenoproteins. Selenoproteins play critical roles in reproduction, thyroid hormone metabolism, DNA synthesis, and protection from oxidative damage. Selenium occurs in two forms: inorganic (selenate and selenite) and organic (selenomethionine and selenocysteine). Both forms can be good dietary sources of selenium. Soils contain inorganic selenites and selenates which are absorbed by plants and converted to organic forms, mostly selenocysteine, selenomethionine, and their methylated derivatives.
Clinical Pharmacology
Most selenium in animal and human tissues is stored as selenomethionine in skeletal muscle, accounting for approximately 28% to 46% of total body selenium stores. Selenocysteine and selenite are reduced to hydrogen selenide, then converted to selenophosphate prior to selenoprotein biosynthesis.
Selenoproteins have structural and enzymatic roles, most notably as antioxidants and catalysts for the production of active thyroid hormones. Selenium is imperative for proper immune function, and its presence may counteract the development of certain viruses and may inhibit the progression from HIV to AIDS. Selenium is necessary for sperm motility, and adequate selenium intake may reduce the risk of miscarriage. Selenium deficiency is linked to mood disorders, increased cardiovascular disease risk, and chronic diseases associated with elevated inflammation.
Indications and Usage
Lipid Levels
Research from the National Health and Nutrition Examination Survey (NHANES) showed a correlation between low selenium levels and elevated total cholesterol (TC) and triglyceride (TG) levels. A meta-analysis found that supplementation of 200 µg/day of selenium in deficient subjects can decrease TG and TC by 5 and 3 mg, respectively.
Cancer
Studies show mixed results regarding selenium’s role in cancer prevention. Some research suggests a correlation between high serum selenium levels and reduced cancer risk, while other reviews, such as a 2011 Cochrane review, found little support for selenium supplements in cancer prevention.
Hashimoto’s Thyroiditis
Selenium plays a role in thyroid function and iodine metabolism. Studies suggest selenium supplementation can improve thyroid hormone levels and reduce TSH in patients with Hashimoto’s thyroiditis.
Type 2 Diabetes
Some studies suggest a U-shaped relationship between serum selenium levels and the risk of type 2 diabetes, with both low and high levels posing risks. Adequate serum selenium levels may reduce the risk by lowering oxidative stress.
Contraindications
Parenteral selenium should not be given undiluted by direct injection into a peripheral vein because of the risk of infusion phlebitis.
Warnings
Excessive selenium can be toxic. Symptoms of selenium toxicity include brittle hair and nails, garlic breath odor, hair loss, and neuropathy. Severe toxicity can result in liver cirrhosis, pulmonary edema, and death. Acute selenium poisoning can lead to vascular collapse and coma.
Dosage and Administration
Selenium Injection contains 40 µg of selenium per mL. The recommended dosage for metabolically stable adults receiving TPN is 20-40 µg/day. For pediatric patients, the suggested dosage is 3 µg/kg/day. Long-term TPN deficiency has been reversed with 100 µg/day selenium intravenously without toxicity.