Selenium is an element that forms part of an important body enzyme (substances essential for body metabolism), which has an antioxidant action in preventing, for example, breakdown of fats (lipids) to substances that can be damaging to the body. The enzyme probably takes care of what other antioxidantsFind out more about this term like vitamin E have failed to do because they were not present in sufficient amounts. Selenium deficiency has been observed in patients receiving all their nutrition via the veins (parenteral nutrition), but with selenium-poor solutions.'Keshan disease', a disease of heart muscle affecting children, is a selenium-deficiency disease seen in a selenium poor area of North-Eastern China.