Cancer chemopreventive activity and bioavailability of tea and tea polyphenols

Consumption of tea (Camellia sinensis) has been associated with many health benefits including the prevention of cancer. Based on in vitro experiments, many mechanisms have been proposed to account for the cancer chemopreventive activity. The importance of some of these mechanisms in vivo remains in question due to an incomplete understanding of the bioavailability of the polyphenolic compounds in tea. In this article, the literature on the cancer chemopreventive activity of tea and the tea polyphenols is discussed as well as some of the possible mechanisms for this activity. Whereas studies in animal models and with cell lines have demonstrated cancer preventive activity, the epidemiological data remain mixed. This discrepancy may arise from several factors including lifestyle, correlation between animal models and humans, and differences in metabolism among individuals. Results on the bioavailability and biotransformation of the tea polyphenols help explain some of the differences. We hope this article will spark research efforts on some of the important questions regarding tea polyphenol bioavailability and cancer chemoprevention.