Vitamin E: Main functions in human body

Vitamin E is present in human tissues and it is necessary for normal metabolism. It is found to be widely distributed in foods. Vitamin E is the collective term given to a group of fat-soluble compounds first discovered in 1922 by Evans and Bishop; these compounds have distinct antioxidant activities essential for health.

Deficiency of vitamin E in man has not been reported and so there is no recommended daily intake. Vitamin E deficiency occurs only as a result of genetic abnormalities in α–tocopherol transfer protein, as a result of various fat malabsorption syndromes, or as a result of protein-energy malnutrition.

It has numerous important roles within the body because of its antioxidant activity. For example, vitamin E protecting substances such as unsaturated fatty acids, carotene and ascorbic acid, which are easily oxidized.

Vitamin E is an essentially naturally occurring fat-soluble nutrient that is involved in several biological processes such as immunity, protection against tissue damage (hear, nerve, etc) reproduction, growth and development.

Vitamin E helps to prevent arteries from clogging by blocking the conversion of cholesterol into the waxy fat deposits called ‘plaque’ that stick to blood vessel walls. Vitamin E also thins the blood, allowing it to flow more easily through arteries even when plaque is present.

One of the few generally recognized uses for vitamin E is in the treatment of hemolytic anemia in premature babies.

Because of its antioxidant action, vitamin E may help protect against clouding of the lens of the eye (cataracts) and a progressive deterioration in the retina, the back part of the eye (age-related macular degeneration, AMD).

There were also studies indicate that vitamin E may slow the aging process and prevent premature aging by prolonging the useful life of human cells, thus maintaining the function of human organs.

Vitamin E is found in various foods and oils. Nuts, seeds and vegetable oils contain high amounts of α-tocopherol, and significant amounts are also available in green leafy vegetables and fortified cereals.
Vitamin E: Main functions in human body

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

Antioxidant activity of vitamin E

Vitamin E is a fat-soluble vitamin that exists in eight different forms. Each form has its own biological activity, the measure of potency or functional use in the body.

Vitamin E was first discovered in 1922 as a substance necessary for reproduction. Following this discovery, vitamin E was extensively studied, and it has become widely known as a powerful lipid-soluble antioxidant.

 It is actually two sets of four compounds each, the tocopherols (alpha, beta, gamma and delta) and the chemically related tocotrienols (alpha, beta, gamma and delta).

Vitamin E compounds (tocopherols and tocotrienols) are well recognized for their effective inhibition of lipid peroxidation in foods and living cells. Vitamin E is synthesized only by plants: therefore it is a very important dietary nutrient for humans and animals.

α-tocopherol is the most active form of vitamin E in humans, and is a powerful biological antioxidant. It is the major lipid soluble found in cells.

The antioxidative activity of the tocopherols is related to scavenging the free radicals of unsaturated lipids. 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.

Free-radical mediated pathology has been implicated in the development of degenerative diseases, conditions and also aging process.
Antioxidant activity of vitamin E

Roles of coenzyme Q10 in human body

Coenzyme Q10 is a vitamin substance naturally found in all parts of the body the action of which resembles that of vitamin E. It may be an even more powerful antioxidant. It is also called ubiquinone.

Coenzyme Q10 is a fundamental ingredient in the energy production that keeps those trillions of cells running smoothly. A shortage of coenzymes Q10 translates into an energy crunch, with cell running on weak batteries. It aids circulation, stimulates the immune system, increases tissue oxygenation, and has vital anti-aging effects.

Besides generating energy, coenzyme Q10 is one of the body’s most powerful antioxidants. It protects body against radicals, the destructive molecular fragments that cause accelerated aging and degenerative diseases.

Coenzyme Q10 is especially well-known for its ability to prevent cellular damage during and following a heart attack (myocardial ischemia and reperfusion).

There are ten common substances designated coenzyme Qs, but coenzyme Q10 is the only one found in human tissue. Deficiencies of coenzymes Q10 have been linked to periodontal disease, diabetes and muscular dystrophy. Supplemental has ability to counter histamine and therefore beneficial for people with allergies, asthma or respiratory disease.

Coenzyme Q10 is used by many health care professional. To treat anomalies of mental function, such as those associated with schizophrenia and Alzheimer’s disease. It is also benefiting in fighting obesity, candidiasis, multiple sclerosis and diabetes.

Orally it is used therapeutically in the treatment of various cardiovascular disorders, including angina pectoris, hypertension, high blood cholesterol and congestive heart failure.
Roles of coenzyme Q10 in human body

Antioxidants network

The destructive chain reaction started by free radicals can be broken by antioxidants, which are converted by the process into harmless derivatives.

Free radical reactions can be broken down into three stages:
*Initiation
*Propagation
*Determination
In initiation phase free radical reaction can be inhibited by two metalloenzymes: superoxide dismutase and catalase

Antioxidants help to maintain a stable internal environment in plants and animals. There is a dynamic interaction among certain key antioxidants that can be referred as antioxidant network.  These special network antioxidants works together to strengthen body immune system and protect human body from disease.

The body has many natural protective mechanisms and network to contain oxidative damage:
*Antioxidant nutrients such B-carotene, vitamin C and E
*Other small molecules with antioxidant properties, for example, glutathione and uric acid, lipoic acid, Coenzyme Q10
*Enzymes such as superoxide dismutase and glutathione peroxidase.

The network antioxidant can greatly enhance the power of one another. They work at the cellular level.
Antioxidants network 

Ascorbic acid as antioxidant

Ascorbic acid is a water soluble vitamin and has diverse functions in the body including as essential role in the hydroxylation reactions for the synthesis of collagen.

It is widely regarded as an essential antioxidant in the human body has even been called ‘the most important antioxidant in human plasma’.

Ascorbic acid’s function in food systems is complex and depends on a number of factors. Its antioxidants activity is affected by the oxidation-reduction potential of the food system, time, PH, oxygen, trace metals, enzymes, other oxidants, and the concentration of the vitamin in comparison to the concentration of other reactants in the oxidation process.

Antioxidant can be defined as any substance that when present at low concentration compared to those of an oxidizable substrate, significantly delays or prevents oxidation of that substrate.

In-vitro experiments have shown that ascorbic acid can act as a chain breaking antioxidant in lipid peroxidation. Studies of the antioxidant activity of human blood plasma suggest that ascorbic acid is the major extracellular antioxidant.

As an oxygen scavenger, ascorbic acid also serves as a reducing agent. It transfers its hydrogen atoms to oxygen, making the oxygen unavailable for further reaction. In the process, the ascorbic acid is oxidized to dehydroascorbic acid, which in turn can function as an oxidizing agent by removing hydrogen from reducing agents such as sulfhydryl groups.

Ascorbic acid and dehydroascorbic acid are thus reversible forms of vitamin C and both have physiological activity. Further, ascorbic acid may exert a chelating action, binding heavy chemical, if present will promote oxidation. When chelated with heavy metals, ascorbic acid loses its physiological vitamin activity.

Ascorbic acid can also undergo autoxidative destruction especially in the presence of transition metals such as copper and iron, which in turn promotes and accelerates the autoxidation of other macromolecules such as unsaturated lipids.

Ascorbic acid is widely used as an oxygen scavenger and synergist in numerous food applications and has a higher oxidation potential (greater reducing capacity) than most phenolic antioxidants.
Ascorbic acid as antioxidant