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Selenium toxicity, also called selenosis, refers to the condition in which an animal has too much of the trace mineral of selenium in its body. In regards to humans, a small amount of selenium is required for optimal health. It combines with proteins to aid in the creation of antioxidants, the regulation of some thyroid functions and the healthy functioning of the immune system. A complete understanding of selenium toxicity includes knowledge about how animals acquire selenium and the health risks associated with too much selenium.
Selenium can be found in the soil because it is a trace mineral. Plants are the primary source of selenium and the amount of selenium found in them depends on the selenium levels in the soil where they grow. Animals obtain selenium through their diet by consuming plants and grasses rich in selenium or by consuming meat from animals that have eaten plants rich in selenium. In the human diet, some of the most selenium rich foods are Brazil nuts, tuna and beef.
The daily recommended intake of selenium ranges from 15 to 55 micrograms per day depending on age. Infants under 6 months of age should have about 15 micrograms per day, while those who are 7 months to the age of 3 should have approximately 20 micrograms per day. Children from 4 to 8 years old may have 30 micrograms daily and 9 to 13 year olds should have 40 micrograms. People who are age 14 and older have a recommended daily intake of selenium that is 55 micrograms, with women who are pregnant and lactating requiring an extra 10 to 15 micrograms per day.
If too much selenium is ingested, usually more than 400 micrograms per day for adults, selenium toxicity will occur. The most common symptoms associated with selenium toxicity are garlic breath, nausea, hair loss, white blotchy nails, hair loss, irritability and mild nerve damage. Deaths caused by selenium toxicity have been rare, but severe signs include diarrhea, excess salivation and shallow breathing. Deaths that have occurred because of selenosis have been industrial accidents.
Selenium toxicity, especially to the level which causes death, is typically found in livestock who graze in areas that have high amounts of selenium in the soil. The Midwest United States has the highest levels of selenium in the soil. China has little or no selenium in their soil and other areas of the world such as Africa, Russia and South America also have low levels.