Merck Manual

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Selenium Toxicity


Larry E. Johnson

, MD, PhD, University of Arkansas for Medical Sciences

Last full review/revision Dec 2021| Content last modified Sep 2022
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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.

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