P A Morrissey and M Kiely, University College Cork,
© 2005 Elsevier Ltd. All rights reserved.
In 1922, Evans and Bishop discovered a fat-soluble dietary constituent that was essential for the prevention of fetal death and sterility in rats accidentally fed a diet containing rancid lard. This was originally called 'factor X' and 'antisterility factor' but was later named vitamin E. Subsequently, the multiple nature of the vitamin began to appear when two compounds with vitamin E activity were isolated and characterized from wheat germ oil. These compounds were designated a- and ^-tocopherol, derived from the Greek 'tokos' for childbirth, 'phorein' meaning to bring forth, and 'ol' for the alcohol portion of the molecule. Later, two additional tocopherols, 7- and ¿-tocopherol, as well as four toco-trienols were isolated from edible plant oils. After the initial discovery, more than 40 years passed before it was proved that vitamin E deficiency could cause disease in humans and was associated with antioxidant functions in cellular systems. It took another 25 years before the non-antioxidant properties of the vitamin were highlighted.
This article reviews the chemistry of the tocopher-ols; their dietary sources, absorption, transport, and storage; and their metabolic function. In addition, the potential role of dietary or supplemental tocopherol intake in the prevention of chronic disease and possible mechanisms for observed protective effects are discussed. Finally, a summary of the assessment of toco-pherol status in humans, intake requirements, and an overview of the safety of high intakes is provided.
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