Vitamin E is well known as an
antioxidant, with 8 natural
isoforms, such as α-, bgr;-, γ- and δ-
tocopherols and α-, β-, gamma;- and δ-
tocotrienols. It has been suggested that both
tocopherols and
tocotrienols have anti-
tumor effects due to the
antioxidant effect. The results of several studies have indicated that the
tocotrienols may have a stronger bioactivity than the
tocopherols. Both types have shown antiproliferative, proapoptotic and cyclooxygenase-2- inhibiting effects in in vitro studies. Several animal studies have demonstrated that
vitamin E has
cancer-preventing effects. However, clinical trials have not shown similar results for the
cancer prevention effect of
tocopherol. Although the Linxian Trials demonstrated that the supplementation of β-
carotene, α-
tocopherol and
selenium reduced
cancer risk, the beneficial effects of α-
tocopherol on
prostate cancer disappeared after several years in the
Alpha-Tocopherol,
Beta-Carotene Cancer Prevention Study.
Vitamin E, especially
tocotrienols, seems to be a potent agent for
cancer prevention, however no large-scale clinical trial on the
cancer prevention effect of
tocotrienols has been conducted yet. Therefore it is expected that clinical trials overcoming the lower bioavailability of
tocotrienols will be conducted, and it is urgently needed to assess the safety and the efficacy of the administration of the
tocotrienols as a part of a
cancer prevention regimen.