Several recent short-term intervention studies failed to show that vitamin E supplementation was protective against the development of various cancers, most notably lung and prostate cancer. In fact, in the Select study, individuals taking vitamin E supplements showed a 17% higher incidence of prostate cancer. In this study, researchers used a synthetic form of vitamin E known as dl-alpha tocopherol acetate. Some experts have argued that this form of vitamin E has only half the potency of natural forms of vitamin E and thus was a poor candidate for use in this and other trials. Others argue that synthetic vitamin E competes with natural vitamin E (both tocopherols and tocotrienols) for receptor binding sites and other processes, thereby reducing the cell’s vitamin E antioxidant defenses and/or reducing other anticancer effects afforded by natural vitamin E (d-alpha-tocopherol) (1-10, 19). Others have implied that possibly vitamin E succinate should be the form of vitamin E used in intervention trials aimed at reducing cancer incidence, as it is the form of vitamin E with the strongest research support as an anticancer agent.
Adding to the confusion, are recent studies showing that antioxidant supplementation may provide existing cancer cells with a survival advantage and thus, may facilitate the growth of cancer once cancer cells have been initiated. In this respect, it may be that antioxidant supplements reduce free radical build-up in cancer cells, which prevents the induction of programmed cell death (apoptosis).
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