Cancer-preventive activities of tocopherols and tocotrienols.
Carcinogenesis. 2009 Sep 11. Epub 2009 Sep 11. PMID: 19748925
The cancer preventive activity of vitamin E has been studied. Whereas some epidemiological studies have suggested a protective effect of vitamin E against cancer formation, many large scale intervention studies with alpha-tocopherol (usually large doses) have not demonstrated a cancer preventive effect. Studies on alpha-tocopherol in animal models also have not demonstrated robust cancer prevention effects. One possible explanation for the lack of demonstrable cancer preventive effects is that high doses of alpha-tocopherol decrease the blood and tissue levels of gamma- and delta-tocopherols. It has been suggested that gamma-tocopherol, due to its strong anti-inflammatory and other activities, may be the more effective form of vitamin E in cancer prevention. Our recent results have demonstrated that a gamma-tocopherol-rich mixture of tocopherols inhibits colon, prostate, mammary, and lung tumorigenesis in animal models, suggesting that this mixture may have a high potential for applications in the prevention of human cancer. In this review, we discuss biochemical properties of tocopherols, results of possible cancer preventive effects in humans and animal models, and possible mechanisms involved in the inhibition of carcinogenesis. Based on this information, we propose that a gamma-tocopherol-rich mixture of tocopherols is a very promising cancer preventive agent and warrants extensive future research.