Selenium (Se) is a part of the enzyme glutathione peroxidase, which metabolizes hydroperoxides formed from polyunsaturated fatty acids. Selenium is also a part of the enzymes that deiodinate thyroid hormones. Generally, selenium acts as an antioxidant that works with vitamin E.
Plasma levels of selenium vary from 8 to 25 mcg/dL (0.1 to 0.3 micromoles/L), depending on selenium intake.
At high doses (> 900 mcg/day), selenium causes toxicity.
Diagnosis of selenium toxicity is usually clinical; sometimes blood glutathione peroxidase is measured.
Manifestations include hair loss, abnormal nails, dermatitis, peripheral neuropathy, nausea, diarrhea, fatigue, irritability, and a garlic odor of the breath.
Toxic levels of plasma selenium are not well defined.
Treatment of selenium toxicity involves reducing selenium consumption.
(See also Overview of Mineral Deficiency and Toxicity.)