Vitamin EFrom Wikipedia, the free encyclopedia

Vitamin E refers to a group of compounds that include both tocopherols and tocotrienols.[1] Of the manydifferent forms of vitamin E, -tocopherol is the most common in the North American diet.[2] -Tocopherol canbe found in corn oil, soybean oil, margarine, and dressings.[3][4] -tocopherol, the most biologically active formof vitamin E, is the second-most common form of vitamin E in the diet. This variant can be found mostabundantly in wheat germ oil, sunflower, and safflower oils.[4][5] As a fat-soluble antioxidant, it stops theproduction of reactive oxygen species formed when fat undergoes oxidation.[6][7][8] Regular consumption ofmore than 1,000 mg (1,500 IU) of tocopherols per day[9] may be expected to cause hypervitaminosis E, with anassociated risk of vitamin K deficiency and consequently of bleeding problems.

FormsThe nutritional content of vitamin E is defined by -tocopherol activity. The molecules that contribute-tocopherol activity are four tocopherols and four tocotrienols, identified by the prefixes alpha- (-), beta- (-),gamma- (-), and delta- (-).[10] Natural tocopherols occur in the RRR-configuration only. The synthetic formcontains eight different stereoisomers and is called 'all-rac'--tocopherol.[11] Water soluble forms such asd-alpha-tocopheryl succinate are used as food additive.

-Tocopherol

-Tocopherol is an important lipid-soluble antioxidant. It performs its functions as antioxidant in theglutathione peroxidase pathway,[12] and it protects cell membranes from oxidation by reacting with lipidradicals produced in the lipid peroxidation chain reaction.[7][13] This would remove the free radical intermediatesand prevent the oxidation reaction from continuing. The oxidized -tocopheroxyl radicals produced in thisprocess may be recycled back to the active reduced form through reduction by other antioxidants, such asascorbate, retinol or ubiquinol.[14] However, the importance of the antioxidant properties of this molecule at theconcentrations present in the body are not clear and the reason vitamin E is required in the diet is possiblyunrelated to its ability to act as an antioxidant.[15] Other forms of vitamin E have their own unique properties;for example, -tocopherol is a nucleophile that can react with electrophilic mutagens.[16]

Tocotrienols

Compared with tocopherols, tocotrienols are sparsely studied.[17][18][19] Less than 1% of PubMed papers onvitamin E relate to tocotrienols.[20] The current research direction is starting to give more prominence to thetocotrienols, the lesser known but more potent antioxidants in the vitamin E family. Some studies havesuggested that tocotrienols have specialized roles in protecting neurons from damage[20] and cholesterolreduction[21] by inhibiting the activity of HMG-CoA reductase; -tocotrienol blocks processing of sterolregulatory element-binding proteins (SREBPs).

Oral consumption of tocotrienols is also thought to protect against stroke-associated brain damage in vivo.[22]Until further research has been carried out on the other forms of vitamin E, conclusions relating to the otherforms of vitamin E, based on trials studying only the efficacy of -tocopherol, may be premature.[23]

Functions

Vitamin E - Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Vitamin_E

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