Interactions with other nutrients
Vitamin C in plasma and extracellular fluid is important in reducing the tocopheroxyl radical in cell membranes and plasma lipoproteins back to tocopherol. There is also evidence that a variety of lipid-soluble antioxidants may be important in the antioxidant action of vitamin E in membranes and lipoproteins, including ubiquinone and synthetic antioxidants used in food processing, such as butyl-ated hydroxytoluene and butylated hydroxyanisole. Synthetic antioxidants will prevent or cure a number of the signs of vitamin E deficiency in experimental animals.
There is a considerable overlap between the func-tions of vitamin E and selenium. Vitamin E reduces lipid peroxide radicals to unreactive fatty acids; the selenium-dependent enzyme glutathione peroxidase reduces hydrogen peroxide to water, thus lowering the intracellular concentration of potentially lipid-dam-aging peroxide. A membrane-specific isoenzyme of glutathione peroxidase will also reduce the tocopher-oxyl radical back to tocopherol. Thus, vitamin E acts to remove the products of lipid peroxidation, whereas selenium acts both to remove the cause of lipid per-oxidation and to recycle vitamin E.