Vitamin E has a fundamental role in protecting the body against the damaging effects of reactive oxygen species that are formed metabolically or encountered in the environment. Vitamin E includes two classes of biologically active substances: (1) the tocopherols and (2) the related but less biologically active compounds, the tocotrienols.
The absorption of vitamin E is highly variable, and efficiencies range from 20% to 70%.
As a membrane free radical scavenger, vitamin E is an important component of the cellular antioxidant defense system.
Tocopherols and tocotrienols are synthesized only by plants; plant oils are the best sources of them, with α and γ tocopherols being the forms in most common foods.
The clinical manifestations of vitamin E deficiency vary considerably. In general, the targets of deficiency are the neuromuscular, vascular, and reproductive systems. Vitamin E deficiency, which may take 5 to 10 years to develop, manifests with loss of deep tendon reflexes, impaired vibratory and position sensation, changes in balance and coordination, muscle weakness, and visual disturbances.
Vitamin E is one of the least toxic of the vitamins. Humans and animals seem to be able to tolerate relatively high intakes—at least 100 times the nutritional requirement. The UL for vitamin E in adults is 1000 mg/day.