Vitamin E is a name given to a group of chemicals with the same biological activity. These include alpha, beta, gamma and delta tocopherol and alpha, beta, gamma and delta tocotrienol. Vitamin E is produced in plants through enzymatically driven pathways and this results in the formation of the various vitamin E vitamers, the exact composition of which depends on the plant in question and the enzymes it expresses. Alpha tocopherol is the most biologically active form of vitamin E and is usually the most common dietary form alongside gamma tocopherol. Generally the tocotrienols are present in much lower amounts compared to the tocopherols. Enzymatic synthesis of vitamin E in plants is complex, and this complexity, as with many things in nature, results in a product that is highly specific and ordered. In this regard the vitamin E produced naturally in plants is in the dextrorotatory form (suffixed; D-) that is utilised by humans and other animals for important physiological purposes.
Man has learnt how to synthesise vitamin E artificially in a laboratory. However, unlike plants, man synthesises vitamin E using chemical reactions that are not enzymatically driven. This results in far less specificity in the final product. As a result the vitamin E synthesised by man is a racemic mixture of both levorotatory (suffixed; L-) and dextrorotatory isomers of vitamin E. The distinction between the natural and synthetic forms of vitamin E are important to consider because levorotatory tocopherol isomers cannot be utilised by man or other animals. Artificially synthesised vitamin E is therefore only ~50 % utilisable compared to naturally synthesised vitamin E because it contains only half of its mass as the dextrorotatory isomer of vitamin E. In order to derive the same benefits to health from synthetic vitamin E, twice as much synthetic vitamin E must therefore be taken. Comparisons have been performed in humans subjects and demonstrate the superior bioavailability of natural compared to synthetic vitamin E.
For example, in one study1, researchers reviewed previous studies that has assessed the biological potency of two compounds with vitamin E activity. Each compound was a vitamin E isomer of alpha tocopherol bonded to an acetate group. Such compounds (tocopheryls) are often found in supplements because the bonding process provides a more stable form of the vitamin that can be added to vitamin tablets, something that is not achievable with the alcohol (tocopherol) version of the compound. The data showed that the natural D-alpha-tocopheryl acetate was much more effective at raising plasma levels compared to the DL-alpha tocopheryl acetate. In fact 80 mg of DL-alpha tocopheryl acetate was less effective that both 60 and 15 mg of D-alpha tocopheryl acetate at raining plasma levels in humans. Studies involving animals suggest that the synthetic vitamin E forms might be ~60 % as potent as the natural forms. It is suggested therefore that natural vitamin E be considered if supplements are necessary.
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