Green Tea: Current Knowledge and Issues.

Green tea possesses antioxidant, anti-inflammatory, anticancer, and antimicrobial activities, reduces body weight, and slows down aging. These effects are primarily attributed to catechins contained in green tea leaves, particularly epigallocatechin-3-gallate. However, in humans, the realization of green tea's beneficial effects is limited. In order to summarize and critically analyze the available scientific information about green tea's health benefits and issues related to its use, we conducted an in-depth literature review in scientific databases. A number of in vitro studies reported that green tea catechins modulate various signaling pathways in cells, which is thought to underlie their beneficial effects. However, data on the effects of catechins in humans are scarce, which is partly due to their low stability and oral bioavailability. Furthermore, catechins may also participate in pharmacokinetic interactions when co-administered with certain drugs such as anticancer agents, drugs for cardiovascular diseases, immunosuppressors, etc. As a result, adverse drug reactions or therapy failure may occur. In conclusion, over the years, various approaches have been investigated to optimize catechin intake and to achieve beneficial effects in humans, but to date, the use of catechins for prophylaxis or disease treatment remains limited. Therefore, future studies regarding the possibilities of catechins administration are needed.