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Vitamin E

Vitamin E

Overview

Vitamin E is used to refer to a group of fat-soluble compounds that include both tocopherol
Tocopherol
Tocopherols are a class of chemical compounds of which many have vitamin E activity. It is a series of organic compounds consisting of various methylated phenols...

s and tocotrienol
Tocotrienol
Tocotrienols are members of the vitamin E family. An essential nutrient for the body, vitamin E is made up of four tocopherols and four tocotrienols . The slight difference between tocotrienols and tocopherols lie in the unsaturated side chain having three double bonds in its farnesyl isoprenoid...

s. There are many different forms of vitamin E, of which γ-tocopherol
Gamma-tocopherol
γ-Tocopherol is one of the chemical compounds that is considered vitamin E. As a food additive, it has E number E308.See the main article tocopherol for more information.-See also:* alpha-Tocopherol* beta-Tocopherol* delta-Tocopherol...

 is the most common in the North American diet. γ-Tocopherol can be found in corn oil, soybean oil, margarine and dressings. α-Tocopherol
Alpha-tocopherol
α-Tocopherol is a type of tocopherol with formula C29H50O2. It has E number "E307".α-Tocopherol is a form of vitamin E that is preferentially absorbed and accumulated in humans...

, the most biologically active form of vitamin E, is the second most common form of vitamin E in the North American diet.
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Encyclopedia

Vitamin E is used to refer to a group of fat-soluble compounds that include both tocopherol
Tocopherol
Tocopherols are a class of chemical compounds of which many have vitamin E activity. It is a series of organic compounds consisting of various methylated phenols...

s and tocotrienol
Tocotrienol
Tocotrienols are members of the vitamin E family. An essential nutrient for the body, vitamin E is made up of four tocopherols and four tocotrienols . The slight difference between tocotrienols and tocopherols lie in the unsaturated side chain having three double bonds in its farnesyl isoprenoid...

s. There are many different forms of vitamin E, of which γ-tocopherol
Gamma-tocopherol
γ-Tocopherol is one of the chemical compounds that is considered vitamin E. As a food additive, it has E number E308.See the main article tocopherol for more information.-See also:* alpha-Tocopherol* beta-Tocopherol* delta-Tocopherol...

 is the most common in the North American diet. γ-Tocopherol can be found in corn oil, soybean oil, margarine and dressings. α-Tocopherol
Alpha-tocopherol
α-Tocopherol is a type of tocopherol with formula C29H50O2. It has E number "E307".α-Tocopherol is a form of vitamin E that is preferentially absorbed and accumulated in humans...

, the most biologically active form of vitamin E, is the second most common form of vitamin E in the North American diet. This variant of vitamin E can be found most abundantly in wheat germ oil, sunflower, and safflower oils. It is a fat-soluble antioxidant
Antioxidant
An antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When...

 that stops the production of reactive oxygen species
Reactive oxygen species
Reactive oxygen species are chemically reactive molecules containing oxygen. Examples include oxygen ions and peroxides. Reactive oxygen species are highly reactive due to the presence of unpaired valence shell electrons....

 formed when fat undergoes oxidation.

Health effects


Vitamin E does not decrease mortality
Mortality rate
Mortality rate is a measure of the number of deaths in a population, scaled to the size of that population, per unit time...

, even at large doses, and may slightly increase it. It does not improve blood sugar control in an unselected group of people with diabetes mellitus
Diabetes mellitus
Diabetes mellitus, often simply referred to as diabetes, is a group of metabolic diseases in which a person has high blood sugar, either because the body does not produce enough insulin, or because cells do not respond to the insulin that is produced...

 or decrease the risk of stroke
Stroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...

. Daily supplementation of vitamin E does not decrease the risk of prostate cancer and may increase it.

Deficiency



Vitamin E deficiency can cause:
  • spinocerebellar ataxia
    Spinocerebellar ataxia
    Spinocerebellar ataxia is a progressive, degenerative, genetic disease with multiple types, each of which could be considered a disease in its own right.-Classification:...

  • myopathies
    Myopathy
    In medicine, a myopathy is a muscular disease in which the muscle fibers do not function for any one of many reasons, resulting in muscular weakness. "Myopathy" simply means muscle disease...

  • peripheral neuropathy
  • ataxia
    Ataxia
    Ataxia is a neurological sign and symptom that consists of gross lack of coordination of muscle movements. Ataxia is a non-specific clinical manifestation implying dysfunction of the parts of the nervous system that coordinate movement, such as the cerebellum...

  • skeletal myopathy
  • retinopathy
    Retinopathy
    Retinopathy is a general term that refers to some form of non-inflammatory damage to the retina of the eye. Frequently, retinopathy is an ocular manifestation of systemic disease.-Pathophysiology:Causes of retinopathy are varied:...

  • impairment of the immune response

α-Tocopherol


α-Tocopherol is an important lipid-soluble antioxidant. It performs its functions as antioxidant in what is known by the glutathione peroxidase pathway and it protects cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

s from oxidation by reacting with lipid radicals produced in the lipid peroxidation
Lipid peroxidation
Lipid peroxidation refers to the oxidative degradation of lipids. It is the process in which free radicals "steal" electrons from the lipids in cell membranes, resulting in cell damage. This process proceeds by a free radical chain reaction mechanism...

 chain reaction
Chain reaction
A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self-amplifying chain of events....

. This would remove the free radical intermediates and prevent the oxidation reaction from continuing. The oxidized α-tocopheroxyl radicals produced in this process may be recycled back to the active reduced form through reduction by other antioxidants, such as ascorbate, retinol
Retinol
Retinol is one of the animal forms of vitamin A. It is a diterpenoid and an alcohol. It is convertible to other forms of vitamin A, and the retinyl ester derivative of the alcohol serves as the storage form of the vitamin in animals....

 or ubiquinol
Ubiquinol
Ubiquinol is an electron-rich form of coenzyme Q10.The natural ubiquinol form of coenzyme Q10 is 2,3-dimethoxy-5-methyl-6-poly prenyl-1,4-benzoquinol, where the polyprenylated side chain is 9-10 units long in mammals...

. However, the importance of the antioxidant properties of this molecule at the concentrations present in the body are not clear and it is possible that the reason why vitamin E is required in the diet is unrelated to its ability to act as an antioxidant. Other forms of vitamin E have their own unique properties; for example, gamma-tocopherol is a nucleophile
Nucleophile
A nucleophile is a species that donates an electron-pair to an electrophile to form a chemical bond in a reaction. All molecules or ions with a free pair of electrons can act as nucleophiles. Because nucleophiles donate electrons, they are by definition Lewis bases.Nucleophilic describes the...

 that can react with electrophilic
Electrophile
In general electrophiles are positively charged species that are attracted to an electron rich centre. In chemistry, an electrophile is a reagent attracted to electrons that participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile...

 mutagens.

Vitamin E has many biological functions. The antioxidant function is considered to be the most important function of vitamin E and is the one it is best known for. However, there are other functions that have also been recognized to be of importance. α-Tocopherol has a regulatory effect on enzymatic activities. For instance, protein kinase C
Protein kinase C
Protein kinase C also known as PKC is a family of enzymes that are involved in controlling the function of other proteins through the phosphorylation of hydroxyl groups of serine and threonine amino acid residues on these proteins. PKC enzymes in turn are activated by signals such as increases in...

 (PKC), which plays a role in smooth muscle growth, can be inhibited by α-tocopherol. α-Tocopherol has a stimulatory effect on the dephosphorylation enzyme, protein phosphatase 2A, which in turn, cleaves phosphate groups from PKC leading to its deactivation, bringing the smooth muscle growth to a halt.
Vitamin E also has an effect on gene expression. Macrophages rich in cholesterol are found in the atherogenetic tissue. Scavenger receptor CD36 is a class B scavenger receptor found to be up-regulated by oxidized low density lipoprotein (LDL) and binds it. Treatment with alpha tocopherol was found to down regulate the CD36 scavenger receptor gene expression as well as the scavenger receptor class A (SR-A).
In addition to the effect it has been shown to have on SRA and CD36, α-tocopherol also has an effect on expression of the connective tissue growth factor (CTGF). CTGF gene, when expressed, is responsible for the repair of the wounds and regeneration of the extracellular tissue that is lost or damaged during atherosclerosis. Moreover, vitamin E also plays a role in neurological functions, and inhibition of platelet aggregation and it has even been suggested that the most important function of vitamin E is as a signaling molecule
Cell signaling
Cell signaling is part of a complex system of communication that governs basic cellular activities and coordinates cell actions. The ability of cells to perceive and correctly respond to their microenvironment is the basis of development, tissue repair, and immunity as well as normal tissue...

, and that it has no significant role in antioxidant metabolism.

So far, most studies about vitamin E have supplemented using only alpha-tocopherol, but doing so leads to reduced serum gamma- and delta-tocopherol concentrations. Moreover, a 2007 clinical study involving alpha-tocopherol concluded that supplementation did not reduce the risk of major cardiovascular events in middle aged and older men.

Tocotrienols


Compared with tocopherols, tocotrienols are sparsely studied. Less than 1% of PubMed papers on vitamin E relate to tocotrienols. Current research direction is starting to give more prominence to the tocotrienols, the lesser known but more potent antioxidants in the vitamin E family. Some studies have suggested that tocotrienols have specialized roles in protecting neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...

s from damage and cholesterol reduction by inhibiting the activity of HMG-CoA reductase; delta-tocotrienol blocks processing of sterol regulatory element‐binding proteins (SREBPs).

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

Recommended daily intake


The Food and Nutrition Board at the Institute of Medicine report the following dietary reference intakes for vitamin E:

Infants
  • 0 to 6 months: 4 mg/day
  • 7 to 12 months: 5 mg/day


Children
  • 1 to 3 years: 6 mg/day
  • 4 to 8 years: 7 mg/day
  • 9 to 13 years: 11 mg/day


Adolescents and Adults
  • 14 and older: 15 mg/day


One IU
International unit
In pharmacology, the International Unit is a unit of measurement for the amount of a substance, based on biological activity or effect. It is abbreviated as IU, as UI , or as IE...

 of Vitamin E is 0.67 mg of RRR-alpha-tocopherol, or 0.45 mg of all rac-alpha-tocopherol

Dietary sources and supplements


The following foods are rich in vitamin E:
  • Wheat germ oil
    Wheat germ oil
    Wheat germ oil is extracted from the germ of the wheat kernel, which makes up only 2½% by weight of the kernel Wheat germ oil is particularly high in octacosanol - a 28 carbon long-chain saturated primary alcohol found in a number of different vegetable waxes. Octacosanol has been studied as an...

  • Sunflower oil
    Sunflower oil
    Sunflower oil is the non-volatile oil expressed from sunflower seeds. Sunflower oil is commonly used in food as a frying oil, and in cosmetic formulations as an emollient. Sunflower oil was first industrially produced in 1835 in the Russian Empire.- Composition :Sunflower oil is mainly a...

  • Safflower oil
  • Nuts and nut oils, like almond
    Almond
    The almond , is a species of tree native to the Middle East and South Asia. Almond is also the name of the edible and widely cultivated seed of this tree...

    s and hazelnut
    Hazelnut
    A hazelnut is the nut of the hazel and is also known as a cob nut or filbert nut according to species. A cob is roughly spherical to oval, about 15–25 mm long and 10–15 mm in diameter, with an outer fibrous husk surrounding a smooth shell. A filbert is more elongated, being about twice...

    s
  • Green leafy vegetables, like lettuce
    Lettuce
    Lettuce is a temperate annual or biennial plant of the daisy family Asteraceae. It is most often grown as a leaf vegetable. It is eaten either raw, notably in salads, sandwiches, hamburgers, tacos, and many other dishes, or cooked, as in Chinese cuisine in which the stem becomes just as important...

    , spinach
    Spinach
    Spinach is an edible flowering plant in the family of Amaranthaceae. It is native to central and southwestern Asia. It is an annual plant , which grows to a height of up to 30 cm. Spinach may survive over winter in temperate regions...

    , turnip
    Turnip
    The turnip or white turnip is a root vegetable commonly grown in temperate climates worldwide for its white, bulbous taproot. Small, tender varieties are grown for human consumption, while larger varieties are grown as feed for livestock...

    , beet
    Beet
    The beet is a plant in the Chenopodiaceae family which is now included in Amaranthaceae family. It is best known in its numerous cultivated varieties, the most well known of which is the purple root vegetable known as the beetroot or garden beet...

    , collard, and dandelion greens
  • Tomato
    Tomato
    The word "tomato" may refer to the plant or the edible, typically red, fruit which it bears. Originating in South America, the tomato was spread around the world following the Spanish colonization of the Americas, and its many varieties are now widely grown, often in greenhouses in cooler...

     products
  • Pumpkin
    Pumpkin
    A pumpkin is a gourd-like squash of the genus Cucurbita and the family Cucurbitaceae . It commonly refers to cultivars of any one of the species Cucurbita pepo, Cucurbita mixta, Cucurbita maxima, and Cucurbita moschata, and is native to North America...

  • Sweet potato
    Sweet potato
    The sweet potato is a dicotyledonous plant that belongs to the family Convolvulaceae. Its large, starchy, sweet-tasting, tuberous roots are an important root vegetable. The young leaves and shoots are sometimes eaten as greens. Of the approximately 50 genera and more than 1,000 species of...

     (0.26 mg/100 g so it corresponds to 5.8 kg of potatoes per day of the recommended intake for adults)
  • Rockfish
    Sebastidae
    Sebastidae is a family of marine fish in the order Scorpaeniformes. Their common names include rockfishes, thornyheads and rockcods. Despite the latter name, they are not closely related to the cods in the genus Gadus, nor the rock cod, Lotella rhacina.Not all authorities recognise this family as...

  • Mangoes
  • Asparagus
    Asparagus
    Asparagus officinalis is a spring vegetable, a flowering perennialplant species in the genus Asparagus. It was once classified in the lily family, like its Allium cousins, onions and garlic, but the Liliaceae have been split and the onion-like plants are now in the family Amaryllidaceae and...

  • Broccoli
    Broccoli
    Broccoli is a plant in the cabbage family, whose large flower head is used as a vegetable.-General:The word broccoli, from the Italian plural of , refers to "the flowering top of a cabbage"....

  • Papayas
  • Avocados
  • Kiwifruit
    Kiwifruit
    The kiwifruit, often shortened to kiwi in many parts of the world, is the edible berry of a cultivar group of the woody vine Actinidia deliciosa and hybrids between this and other species in the genus Actinidia....


History


The first use for vitamin E as a therapeutic agent was conducted in 1938 by Widenbauer. Widenbauer used wheat germ oil supplement on 17 premature new born infants suffering from growth failure. Eleven out of the original 17 patients recovered and were able to resume normal growth rates. Later on, in 1948, while conducting experiments on alloxan
Alloxan
Alloxan is an oxygenated pyrimidine derivative. It is present as alloxan hydrate in aqueous solution.-History:...

 effects on rats, Gyorge and Rose noted that the rats receiving tocopherol supplements suffered from less hemolysis
Hemolysis
Hemolysis —from the Greek meaning "blood" and meaning a "loosing", "setting free" or "releasing"—is the rupturing of erythrocytes and the release of their contents into surrounding fluid...

 than those that did not receive tocopherol. In 1949, Gerloczy administered all-rac-α-tocopheryl acetate
Tocopheryl acetate
Tocopheryl acetate, also known as vitamin E acetate, is a common vitamin supplement with the molecular formula C31H52O3 . It is the ester of acetic acid and tocopherol . It is often used in dermatological products such as skin creams...

 to prevent and cure edema
Edema
Edema or oedema ; both words from the Greek , oídēma "swelling"), formerly known as dropsy or hydropsy, is an abnormal accumulation of fluid beneath the skin or in one or more cavities of the body that produces swelling...

. Methods of administration used were both oral, that showed positive response, and intramuscular, which did not show a response. This early investigative work on the benefits of vitamin E supplementation was the gateway to curing the vitamin E deficiency caused hemolytic anemia
Hemolytic anemia
Hemolytic anemia is a form of anemia due to hemolysis, the abnormal breakdown of red blood cells , either in the blood vessels or elsewhere in the human body . It has numerous possible causes, ranging from relatively harmless to life-threatening...

described during the 1960s. Since then, supplementation of infant formulas with vitamin E has eradicated this vitamin’s deficiency as a cause for hemolytic anemia.

External links

  • Vitamin E Medline Plus, Medical Encyclopedia, U.S. National Library of Medicine
  • Vitamin E Office of Dietary Supplements, National Institutes of Health