Vitamin E occurs in the diet as a mixture of several closely related compounds, called tocopherols. Ninety percent of vitamin E present in human tissues is in the form of the natural isomer, α-tocopherol. Tocopherols have a substituted chromanone nucleus, with a polyisoprenoid side chain of variable length; usually three isoprene units (Fig. 10.3). The richest sources of naturally occurring vitamin E are vegetable oils and nuts. In European folklore, vitamin E has been associated with fertility and sexual activity. This is certainly true in other animal species where vitamin E plays a role in sperm production and egg implantation, but this is not the case in man.
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| Vitamin E is a membrane antioxidant
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| Figure 10.3 Structure of vitamin E family (tocopherols). R1-R3 can be methylated in a variety of combinations. The polyisoprenoid side chain occurs at R4. Me, methyl. |
| Vitamin E functions as an antioxidant, in particular a membrane antioxidant, and as such it is associated with the membrane lipid structure. It is the most abundant natural
antioxidant and, owing to its lipid solubility, it is associated with all lipid-containing structures: membranes, lipoproteins and fat deposits. It is absorbed from the diet with other lipid components and there is no specific transport protein. In the circulation it is associated with lipoproteins. Fat malabsorption reduces the body fat content of vitamin E and, after a prolonged period, neurologic symptoms related to vitamin E deprivation have been reported. Low vitamin E intake in pregnancy and newborn infants is associated with hemolytic anemia. This is usually found only in preterm infants fed on formula milk with low vitamin E content. Deficiency of vitamin E in premature infants causes haemolytic anaemia, thrombocytosis and edema. There is little evidence in support of vitamin E toxicity.
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