Cancer prevention by tea and tea constituents

During the Tang Dynasty (618 to 906 A.D.), tea became a popular drink in China. In 1644, sailors began bringing tea packages from the Far East to the United Kingdom. Tea replaced ale as the national drink of England. Tea bushes arrived in the United States in 1799, and by 1901, Thomas Sullivan developed the first tea bag. Now tea is second only to water as the world’s most consumed beverage. All tea comes from Camellia sinensis, a warm-weather evergreen. Tea is grown in thousands of tea gardens around the world, resulting in thousands of flavorful variations. Leaves of the C. sinensis plant are dried for stability and shelf life. The mode of processing the fresh tea leaves and their extent of exposure to oxygen determine the types of tea. In the manufacturing of green tea, the leaves are steamed, rolled, and dried, avoiding oxidation. In black tea production, the tea leaves are crushed to allow enzyme-catalyzed oxidation. In this process, polyphenolic compounds in tea leaves undergo polymerization and other chemical reactions that result in distinctive color and taste. Oolong tea falls somewhere between green and black teas, in that the polyphenols in leaves are only partially oxidized. Tea is also divided by grades, determined by the leaf size.