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Selenium Excess

ByLarry E. Johnson, MD, PhD, University of Arkansas for Medical Sciences
Reviewed/Revised May 2025
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Selenium excess is rare and is caused by consuming too much of the mineral selenium.

Selenium occurs in all tissues. Selenium works with vitamin E as an antioxidant. It helps protect cells against damage by free radicals, which are reactive by-products of normal cell activity. Selenium may help protect against some cancers. Selenium is also necessary for the thyroid gland to function normally.

Taking more than 900 micrograms of a nonprescription selenium supplement each day can have harmful effects. Symptoms of Taking more than 900 micrograms of a nonprescription selenium supplement each day can have harmful effects. Symptoms ofselenium toxicity are mainly gastrointestinal upset, including nausea, vomiting, and diarrhea. Other symptoms include hair loss, abnormal nails, a rash, fatigue, and nerve damage. The breath may smell like garlic.

The diagnosis of selenium excess is based on a history of selenium supplementation and symptoms. Blood or urinaryexcess is based on a history of selenium supplementation and symptoms. Blood or urinary selenium levels can be measured.

Treatment of selenium excess involves reducing selenium consumption.

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