vitamin e and scars

Tocopherols (or TCP) 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. Because the vitamin activity was first identified in 1936 from a dietary fertility factor in rats, it was given the name "tocopherol" from the Greek words “τοκος” , and “φορειν”, meaning in sum "to carry a pregnancy," with the ending "-ol" signifying its status as a chemical alcohol.

Tocotrienols, which are related compounds, may also have vitamin E activity. All of these various derivatives with vitamin activity may correctly be referred to as "vitamin E." Tocopherols and tocotrienols are fat-soluble antioxidants but also seem to have many other functions in the body.

The compound α-tocopherol, a common form of tocopherol added to food products, is denoted by the E number E307.

Forms

Vitamin E exists in eight different forms, four tocopherols and four tocotrienols. All feature a chromanol ring, with a hydroxyl group that can donate a hydrogen atom to reduce free radicals and a hydrophobic side chain which allows for penetration into biological membranes. Both the tocopherols and tocotrienols occur in alpha, beta, gamma and delta forms, determined by the number of methyl groups on the chromanol ring. The tocotrienols differ from the analogous tocopherols by the presence of three double bonds in the hydrophobic side chain. Each form has slightly different biological activity.

As a food additive, tocopherol is labeled with these E numbers: E307 (α-tocopherol), E308 (γ-tocopherol), and E309 (δ-tocopherol).

Alpha-tocopherol

Main article: alpha-Tocopherol

Alpha-tocopherol is the form of vitamin E that is preferentially absorbed and accumulated in humans. The measurement of "vitamin E" activity in international units (IU) was based on fertility enhancement by the prevention of spontaneous abortions in pregnant rats relative to alpha-tocopherol.

There are three stereocenters in alpha-tocopherol, so this is a chiral molecule. The eight stereoisomers of alpha-tocopherol differ in the arrangement of groups around these stereocenters. In the image of RRR-alpha-tocopherol below, all three stereocenters are in the R form. However, if the middle of the three stereocenters were changed (so the hydrogen was now pointing down and the methyl group pointing up), this would become the structure of RSR-alpha-tocopherol. RSR-alpha-tocopherol and RRR-alpha-tocopherol are mirror-images of each other. These stereoisomers can also be named in an alternative older nomenclature, where the stereocenters are either in the d or l form.

1 IU of tocopherol is defined as ⅔ milligrams of RRR-alpha-tocopherol (formerly named d-alpha-tocopherol or sometimes ddd-alpha-tocopherol). 1 IU is also defined as 1 milligram of an equal mix of the eight stereoisomers, which is a racemic mixture called all-rac-alpha-tocopheryl acetate. This mix of stereoisomers is often called dl-alpha-tocopheryl acetate, even though it is more precisely dl,dl,dl-alpha-tocopheryl acetate). However, 1 IU of this racemic mixture is not now considered equivalent to 1 IU of natural (RRR) α-tocopherol, and the Institute of Medicine and the USDA now convert IU's of the racemic mixture to milligrams of equivalent RRR using 1 IU racemic mixture = 0.45 "milligrams α-tocopherol".

Tocotrienols

Tocotrienols, with four d- isomers, although less commonly known, also belong to the vitamin E family. The four tocotrienols have structures corresponding to the four tocopherols, except with an unsaturated bond in each of the three isoprene units that form the hydrocarbon tail, whereas Tocopherols have a saturated phytyl tail. Tocotrienol has been subject to fewer clinical studies and seen less research as compared to tocopherol. However, there is growing interest in the health effects of these compounds.

History

During feeding experiments with rats Herbert McLean Evans concluded in 1922 that besides vitamins B and C, an unknown vitamin existed. Although every other nutrition was present, the rats were not fertile. This condition could be changed by additional feeding with wheat germ. It took several years until 1936 when the substance was isolated from wheat germ and the formula C₂₉H₅₀O₂ was determined. Evans also found that the compound reacted like an alcohol and concluded that one of the oxygen atoms was part of an OH (hydroxyl) group. As noted in the introduction, the vitamin was given its name by Evans from Greek words meaning "to bear young" with the addition of the -ol as an alcohol. The structure was determined shortly thereafter in 1938.

Recommended amounts

The U.S. Dietary Reference Intake (DRI) Recommended Daily Amount (RDA) for a 25-year old male for Vitamin E is 15 mg/day. The DRI for vitamin E is based on the alpha-tocopherol form because it is the most active form as originally tested. Results of two national surveys, the National Health and Nutrition Examination Survey (NHANES III 1988-91) and the Continuing Survey of Food Intakes of Individuals (1994 CSFII) indicated that the dietary intakes of most Americans do not provide the recommended amounts of vitamin E. However, a 2000 Institute of Medicine (IOM) report on vitamin E states that intake estimates of vitamin E may be low because energy and fat intake is often underreported in national surveys and because the kind and amount of fat added during cooking is often not known. The IOM states that most North American adults get enough vitamin E from their normal diets to meet current recommendations. However, they do caution individuals who consume low fat diets because vegetable oils are such a good dietary source of vitamin E. "Low-fat diets can substantially decrease vitamin E intakes if food choices are not carefully made to enhance alpha-tocopherol intakes". Vitamin E supplements are absorbed best when taken with meals.

Because vitamin E can act as an anticoagulant and may increase the risk of bleeding problems, many agencies have set an upper tolerable intake level (UL) for vitamin E at 1,000 mg (1,500 IU) per day.

Sources

In foods, the most abundant sources of vitamin E are vegetable oils such as palm oil, sunflower, corn, soybean, and olive oil. Nuts, sunflower seeds, seabuckthorn berries, kiwifruit, and wheat germ are also good sources. Other sources of vitamin E are whole grains, fish, peanut butter, goats milk, and green leafy vegetables. Fortified breakfast cereals are also an important source of vitamin E in the United States. Although originally extracted from wheat germ oil, most natural vitamin E supplements are now derived from vegetable oils, usually soybean oil.

The content of Vitamin E for rich sources follows:

Wheat germ oil (215.4 mg/100 g)
Sunflower oil (55.8 mg/100 g)
Almond oil (39.2 mg/100 g)
Hazelnut (26.0 mg/100 g)
Walnut oil (20.0 mg/100 g)
Peanut oil (17.2 mg/100 g)
Olive oil (12.0 mg/100 g)
Peanut (9.0 mg/100 g)
Pollard (2.4 mg/100 g)
Corn (2.0 mg/100 g)
Asparagus (1.5 mg/100 g)
Oats (1.5 mg/100 g)
Chestnut (1.2 mg/100 g)
Coconut (1.0 mg/100 g)
Tomatoes (0.9 mg/100 g)
Carrots (0.6 mg/100 g)
Goat's milk (0.1 mg/100ml)

Deficiency

Main article: Vitamin E deficiency

Vitamin E deficiency causes neurological problems due to poor nerve conduction. These include neuromuscular problems such as spinocerebellar ataxia and myopathies. Deficiency can also cause anemia, due to oxidative damage to red blood cells.

Supplements

Commercial vitamin E supplements can be classified into several distinct categories:

Fully synthetic vitamin E, "dl-alpha-tocopherol", the most inexpensive, most commonly sold supplement form usually as the acetate ester;
Semi-synthetic "natural source" vitamin E esters, the "natural source" forms used in tablets and multiple vitamins. These are highly fractionated d-alpha tocopherol or its esters, often made by synthetic methylation of gamma and beta d,d,d tocopherol vitamers extracted from plant oils.
Less fractionated "natural mixed tocopherols" and high d-gamma-tocopherol fraction supplements

Synthetic all-racemic

Synthetic vitamin E derived from petroleum products is manufactured as all-racemic alpha tocopheryl acetate with a mixture of eight stereoisomers. In this mixture, one alpha-tocopherol molecule in eight molecules are in the form of RRR-alpha-tocopherol (12.5% of the total).

The 8-isomer all-rac vitamin E is always marked on labels simply as dl-tocopherol or dl-tocopheryl acetate, even though it is (if fully written out) actually dl,dl,dl-tocopherol. The present largest manufacturers of this type are DSM and BASF.

(An earlier semisynthetic vitamin E actually contained 50% d,d,d-alpha tocopherol moiety and 50% l,d,d-alpha-tocopherol moiety, as synthesized by an earlier process which

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