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Merck Manual

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Selenium Excess


Larry E. Johnson

, MD, PhD, University of Arkansas for Medical Sciences

Last full review/revision Jun 2020| Content last modified Jun 2020
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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. (See also Overview of Minerals.)

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

The diagnosis of selenium excess is based on symptoms, particularly rapid hair loss.

Treatment of selenium excess involves reducing selenium consumption.

(See also Overview of Minerals.)

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