Mechanism of vitamin E as antioxidant

Antioxidants such as vitamin E act to protect body cells against the effects of free radicals, which are potentially damaging by-products of the body's metabolism. Vitamin E serves as one of the body’s chief defenses against damage by free radicals.

Vitamin E occurs in nature in at least eight different isoforms: α, β, γ -and 𝛿 -tocopherols and α, β, γ- and 𝛿 -tocotrienols. Tocotrienols differ from the corresponding tocopherols only in their aliphatic tail. Free radical scavenging reactions of α tocopherol take place via the α -tocopheroxyl radical as an intermediate.

Tocopherol isomers are chain-breaking antioxidants. α-tocopherol, the most biologically active and abundant form of vitamin E in vivo, efficiently transfers a hydrogen atom to a lipid free radical, such as peroxyl, alkoxyl, and carbon~centered radicals, giving the corresponding non-radical product of the lipid and an α -tocopheroxyl radical.

Most notably, vitamin E prevents the oxidation of the polyunsaturated fatty acids, but is protects other lipids and related components (e.g. vitamin A) as well. It therefore occupies a unique position in the arsenal of natural antioxidants providing protection against various diseases.
Mechanism of vitamin E as antioxidant

Biological activity of vitamin E

Vitamin E, the most important lipid-soluble antioxidant, was discovered at the University of California at Berkeley in 1922 in the laboratory of Herbert M. Evans. At least eight vitamin E isoforms with biological activity have been isolated from plant sources.

Vitamin E is a naturally occurring free radical scavenger and its most widely accepted biological function is its antioxidant property. Vitamin E inhibits the free radical chain peroxidation of polyunsaturated lipids in membranes and lipoprotein.

The polyunsaturated linoleic, arachidonic and docosahexaenoic acids are examples of lipids sensitive to peroxidation. All natural forms and synthetic stereoisomers of vitamin E exhibit to varying degrees the ability to inhibit lipid peroxidation as chain-breaking antioxidants.

α-tocopherol

Tocopherols and tocotrienols are part of an interlinking set of antioxidant cycles, which has been termed the antioxidant network. Although the antioxidant activity of tocotrienols is higher than that of tocopherols, tocotrienols have a lower bioavailability after oral ingestion. Tocotrienols penetrate rapidly through skin and efficiently combat oxidative stress induced by UV or ozone.

Vitamin E (α-tocopherol) has the highest biological activity and reverses vitamin E deficiency symptoms in humans. α-tocopherol is a required nutrient for humans because it is needed 20 for prevention of vitamin E deficiency symptoms including neuropathy and hemolytic anemia.
Biological activity of vitamin E