According to the National Institutes of Health, abnormally high levels of selenium in the blood can cause a condition called selenosis, characterized by symptoms such as hair loss, garlic breath odor, white blotchy nails, gastrointestinal problems, irritability, fatigue and nerve damage. The effects of selenium poisoning are similar to the symptoms of arsenic poisoning, though symptoms may vary depending on factors such as the type of selenium ingested as well as the dose. Other symptoms of selenium toxicity include lightheadedness, facial flushing, tremor, muscle tenderness, liver and kidney problems and blood clotting problems.

Toxicity

Although selenium is required for health, like other nutrients, high doses of selenium can be toxic. Acute and fatal toxicities have occurred with accidental or suicidal ingestion of gram quantities of selenium. Clinically significant selenium toxicity was reported in 13 individuals after taking supplements that contained 27.3 milligrams (27,300 mcg) per tablet due to a manufacturing error. Chronic selenium toxicity (selenosis) may occur with smaller doses of selenium over long periods of time. The most frequently reported symptoms of selenosis are hair and nail brittleness and loss. Other symptoms may include gastrointestinal disturbances, skin rashes, a garlic breath odor, fatigue, irritability, and nervous system abnormalities. In an area of China with a high prevalence of selenosis, toxic effects occurred with increasing frequency when blood selenium concentrations reached a level corresponding to an intake of 850 mcg/day. The Food and Nutrition Board (FNB) of the Institute of Medicine recently set the tolerable upper intake level (UL) for selenium at 400 mcg/day in adults based on the prevention of hair and nail brittleness and loss and early signs of chronic selenium toxicity (15). The UL of 400 mcg/day for adults (see table below) includes selenium obtained from food, which averages about 100 mcg/day for adults in the U.S., as well as selenium from supplements.