Catechin is major substance of tannin and is a type of antioxidant(poly-phenol) found in great abundance in the tea leaves including black tea, Chinese woo-long tea, etc. However, the content rate of green tea is much higher than other types of tea due to the different processing methods; green tea is only steamed and dried, whereas black tea and woo-long tea are fermented during the processing which causes the loss of beneficial nutrients. A cup of green tea (120ml) can contain up to 80mg of catechin. Catechins are also found in other foods such as red wine, chocolate, berries and apples in smaller amounts.
Health experts in Japan have been researching the health benefits of tea catechin and the association of tea with long life and health since 1990s, after they studied a large groups of people in a comprehensive survey they have found that people who drink lots of green tea have a longer and healthier life than people who don’t drink much green tea.