Catechin

Catechins are polyphenolic antioxidant plant metabolites, specifically flavonoids called flavan-3-ols. Although present in numerous plant species, the largest source in the human diet is from various teas derived from the tea-plant Camellia sinensis.

Catechin, epicatechin, gallocatechin, epigallocatechin, and the gallates
Catechin and epicatechin are epimers, with (-)-epicatechin and (+)-catechin being the most common optical isomers found in nature. Catechin was first isolated from the plant extract catechu, from which it derives its name. Heating catechin past its point of decomposition releases pyrocatechol, which explains the common origin of the names of these compounds.

Epigallocatechin and gallocatechin contain an additional phenolic hydroxyl group when compared to epicatechin and catechin, respectively, similar to the difference in pyrogallol compared to pyrocatechol.

Catechin gallates are gallic acid esters of the catechins; such as EGCG (epigallocatechin gallate), which is commonly the most abundant catechin in tea.

Sources of catechins
Catechins constitute about 25% of the dry weight of fresh tea leaf, although total catechin content varies widely depending on clonal variation, growing location, seasonal/ light variation, and altitude. They are present in nearly all teas made from Camellia sinensis, including white tea, green tea, black tea and Oolong tea.

Catechins are also present in the human diet in chocolate, fruits, vegetables and wine and are found in many other plant species.

Health benefits of catechins
The health benefits of catechins have been studied extensively in humans and in animal models. Reduction in atherosclerotic plaques was seen in animal models. Reduction in carcinogenesis was seen in vitro.

Many studies on health benefits have been linked to the catechin content. According to Norman Hollenberg, professor of medicine at Harvard Medical School, epicatechin can reduce the risk of four of the major health problems: stroke, heart failure, cancer and diabetes. He studied the Kuna people in Panama, who drink up to 40 cups of cocoa a week, and found that the prevalence of the "big four" is less than 10%. He believes that epicatechin should be considered essential to the diet and thus classed as a vitamin.Science Daily March 12, 2007

According to one researcher epigallocatechin-3-gallate is an antioxidant that helps protect the skin from UV radiation-induced damage and tumor formation.

A study on green-tea catechins is reviewed here: http://www.sciencedaily.com/releases/2007/08/070810194923.htm