ABSTRACT
Tea is the most consumed beverage in the world, next to water. Of the total amount of tea undergoing different manufacturing processes produced and consumed globally, 78% is black tea, 20% is green tea, and <2% is oolong tea (Ju et al. 2007). Black tea is fully fermented, oolong tea is partially fermented, and green tea is not at all fermented but only steamed. Green tea is consumed mostly in China, Japan, India, and a few countries in North Africa and the Middle East, black tea is consumed primarily in Western countries and in some Asian countries, while oolong tea consumption is limited to southeastern China and Taiwan (Khan et al. 2008). Green tea was always considered as a healthy beverage in ancient Chinese medicine. In the past few years, the chemical constituents of green tea received great scientic attention for their benecial health effects and lack of toxicity. The intake of green tea has been shown to lower blood pressure and the risk of cardiovascular diseases, prevent the development of atherosclerosis, improve lipid prole, and have antithrombotic and anti-inammatory properties. Green tea contains characteristic polyphenolic compounds, (–)-epigallocatechin-3-gallate (EGCG), (–)-epigallocatechin (EGC), (–)-epicatechin3-gallate (ECG), and (–)-epicatechin (EC). These compounds are commonly known as catechins. Most of the studies carried out with green tea are with green tea polyphenols (GTPs) or individual catechins, especially EGCG. Green tea has received considerable attention due to its plentiful, scientically proven, favorable effects on the health of humans. One cup of green tea contains 200 mg of EGCG, which has been reported to have chemopreventive effects against numerous cancers (Yang et al. 2002, 2009). Appropriate drinking of green tea is 3 to 5 cups per day, which provides a minimum of 250 mg per day of catechins (Boehm et al. 2009). The effects of green tea on the activities of various receptor tyrosine kinases and pathways of signal transduction have also been reported (Khan and Mukhtar 2008). EGCG has also been shown to inhibit tumor invasion and angiogenesis, critical for tumor growth and metastasis (Khan and Mukhtar 2010). In this chapter, we will discuss the effects of green tea and its polyphenols against cancers of the prostate, skin, lung, liver, breast, and gastrointestinal tract.
