METABOLISM AND REQUIREMENT OF VITAMIN-E

Alpha-tocopherol (vitamin E), the main lipid-soluble antioxidant in bi ological membranes, reacts readily with radical and non-radical oxidan ts. Such reactions may lead to alpha-tocopherol consumption, defined a s loss of antioxidant action. Irreversibly oxidized metabolites excret ed via the bile into the feces are tocopheryl quinone, epoxyquinones, and products of dimeric and trimeric structures. A alpha-tocopherol ba lance cannot be calculated, due to low intestinal absorption, enterohe patic circulation, and microbial metabolism in the intestine. For thes e reasons physiological vitamin E requirement cannot be derived from t he alpha-tocopherol turnover. A common approach towards dietary recomm endations is based on the PUFA - vitamin E relationship. Recently it w as discovered that not the Simon metabolites, but -tetramethyl-2-(2'-c arboxyethyl)-6-hydroxy-chroman (alpha-CEHC) is the major urinary excre tion product. Our finding that excretion of this metabolite depends on the plasma tocopherol concentration has been reason to conclude that alpha-CEHC may be a marker of the optimum prophylactic vitamin E intak e.