Vitamin E (tocopherols and tocotrienols) (natural-occurring antioxidant; bright and dark side)

Vitamin E is extensively available in the natural world and is produced by prototrophs such as plants, algae, and blue-green algae. Vitamin E is used as a dietary supplement, an antioxidant food stabilizer, a pharmaceutical additive, and as a preservative in livestock feed. There are several types of vitamin E that can be differentiated by the position and number of the methyl functional group, and each form has a unique biological role. The function of antioxidants such as vitamin E is to defend cells from the effects of oxidative stress. Vitamin E is a free radical scavenger and is converted to vitamin E radical, which is then converted back to vitamin E by ascorbic acid. Vitamin E was discovered by Evans and Bishop in 1922 since that it has proved to be an effective nutrient for reproduction. It is also possible for vitamin E to act by a mechanism which is not directly linked to inhibition of oxidation. Such non-antioxidant actions of vitamin E may be a result of gene regulation and specific cell signaling. The function of vitamin E in cellular signaling, especially its biological impact is undoubtedly an imperative subject for future studies. The explicit roles of the several isomers and esters of vitamin E analogues should also be the subjects of future studies.