Relationship between vitamin E requirement and polyunsaturated fatty acid intake in man: a review

Vitamin E is the general term for all tocopherols and tocotrienols, Of whic h alpha-iocopherol is the natural and biologically most active form. Althou gh gamma-tocopherol makes a significant contribution to the Vitamin E CONTE NT in foods, it is less effective in animal and human tissues, where alpha- tocopherol is the most effective chain-breaking lipid-soluble antioxidant. The antioxidant function of Vitamin E is critical for the prevention of oxi dation of tissue PUFA. Animal experiments have shown that increasing the degree Of dietary fatty a cid unsaturation increases the peroxidizability of the lipids and reduces t he time required to develop symptoms of vitamin E deficiency. From these ex periments, relative amounts of vitamin E required to protect the Various fa tty acids from being peroxidized, could he estimated. Since systematic studies on the vitamin E requirement in relation to PUFA c onsumption have not been performed in man, recommendations for vitamin E in take are based On animal experiments and human food intake data. An intake of 0.6 mg alpha-tocopherol equivalents per gram linoleic acid iS generally Seen as adequate for human adults, The minimum vitamin E requirement at con sumption of fatty acids with a higher degree of saturation can be calculate d by a formula, which takes into account the peroxidizability of unsaturate d fatty acids and is based on the results of animal experiments. There are however, no clear data on the Vitamin E requirement of humans con suming the more unsaturated fatty acids as for instance EPA (20:5, n-3) and DHA (22:6. n-3). Studies investigating the effects Of EPA and DHA suppleme ntation have shown an increase in Lipid peroxidation, although amounts of v itamin E were present that are considered adequate in relation to the calcu lated oxidative potential Of these fatty acids. Further- more, a calculatio n of the vitamin E requirement, using recent nutritional intake data, shows that a reduction in total fat intake with a concomitant increase in PUFA c onsumption, including EPA and DHA, will result in an increased amount of vi tamin E required. In addition, the methods used in previous studies investigating vitamin E r equirement and PUFA consumption (for instance erythrocyte hemolysis), and t he techniques used to assess lipid peroxidation (e.g: MDA analysis), may be unsuitable to establish a quantitative relation between vitamin E intake a nd consumption of highly : unsaturated fatty acids. Therefore, further stud ies are required to establish the vitamin E requirement when the intake of longer-chain more-unsaturated fatty acids is increased. For this purpose it is necessary to use functional techniques based on the measurement of lipi d peroxidation in vivo. Until these data are available, the widely used rat io of at least 0.6 mg alpha-TE/g PUFA is suggested. Higher levels may be ne cessary, however, for fats that are rich in fatty acids containing more tha n two double bonds.