What Is Selenium Toxicity?

The NIH Office of Dietary Supplements says selenosis is the result of chronically high intakes of selenium, that it is most commonly characterized by hair loss and nail brittleness or loss, and that other signs and symptoms can include a garlic odor on the breath, a metallic taste in the mouth, skin rash, nausea, diarrhea, fatigue, irritability and nervous system abnormalities. It says the Tolerable Upper Intake Level for selenium is 400 mcg for adults, and, citing USDA FoodData Central, that Brazil nuts have an average of 544 mcg of selenium per ounce, although values from other analyses vary widely.

ATSDR says short-term oral exposure to high concentrations of selenium may cause nausea, vomiting and diarrhea, and that the major signs of selenosis are hair loss, nail brittleness, and neurological abnormalities such as numbness and other odd sensations in the extremities.

The NIH Office of Dietary Supplements says that in 2008, 201 people experienced severe adverse reactions from taking a liquid dietary supplement that contained 200 times the labeled amount of selenium. A peer-reviewed investigation of that outbreak in Archives of Internal Medicine identified 201 cases in 10 states, with one person hospitalized, a median estimated selenium dose of 41,749 micrograms a day, and frequently reported symptoms including diarrhea, fatigue, hair loss, joint pain, nail discoloration or brittleness, and nausea. Among patients interviewed 90 days or more after their symptoms began, lasting symptoms included fingernail discoloration and loss in 52%, fatigue in 35%, hair loss in 29%, joint pain in 26%, and memory loss and muscle aches in 22% each.