The Chinese belief that drinking tea promotes good health and longevity is gaining scientific merit Oolong tea is one of the three types of tea that is manufactured from tea leaves; the others are black and green teas. Green tea, which is consumed largely in Asia, is processed to minimize fermentation, whereas black tea, which is popular in western countries, is fermented to produce the characteristic flavor components. Oolong tea is less fermented than black tea. It is sold commercially in the United States and is often served in Chinese restaurant . Tea is one of the most frequently consumed beverages worldwide, yet very little is known about its metabolic effects in humans. Caffeine is generally regarded as the major metabolically active compound in tea. No consistent scientific evidence links moderate caffeine consumption to any health risks, including cancer, cardiovascular disease, fibrocystic breast disease or birth defects. Some individuals are sensitive to caffeine and find that it induces jitters, sleeplessness or irritation to the gastrointestinal tract but others consume it specifically because it is a mild stimulant and increases alertness and metabolic rate.