Vitamin E is required by most animal species, including humans. It was discovered in 1922, when rats fed a purified diet without vitamin E were unable to reproduce. Wheat germ oil added to their diet restored their fertility. Later, vitamin E was isolated and was originally called the "antisterility" vitamin or tocopherol. The word "tocopherol" comes from the Greek words tokos, meaning "offspring," and phero, meaning "to bear." Hence, tocopherol literally means "to bear children," a reference to the rats' renewed ability to reproduce. Alpha-tocopherol is the chemical name for the most active form of vitamin E, at least in rats. In humans, new research suggests that the gamma and delta fractions and the tocotrienols may be much more important for cardiovascular health.
Vitamin E functions primarily as an antioxidant by protecting against damage to cell membranes. Without vitamin E, the cells of the body would be quite susceptible to damage. Nerve cells would be particularly vulnerable. Severe vitamin E deficiency is quite rare, but there are a number of conditions in which low levels of vitamin E have been reported, including acne, anemia, some cancers, gallstones, Lou Gehrig's disease, muscular dystrophy, Parkinson's disease, and Alzheimer's disease.