Green tea: Varieties, production and health benefits

Tea is one of the most popular beverages consumed worldwide. Based on themanufacturing process, green, black, and oolong tea are the 3 major commercial types oftea. Green tea, without any fermentation, is processed to prevent the oxidation of greenleaf polyphenols, although most polyphenols are oxidized in black tea or oolong teaduring fermentation production. This fermentation converts catechin to theaflavins andthearubigins, consequently decreasing the catechin content. The polyphenols present ingreen tea are flavonols, commonly known as catechins, which contain 5 major subtypes:catechin, epicatechin, epicatechin gallate, epigallocatechin, and epigallocatechin gallate(EGCG). These natural compounds show diverse chemical and biologic activities, andare nontoxic under daily dose. In recent years, evidences from epidemiologic and animalstudies have shown chemopreventive and anticancer potential of dietary polyphenols.Several studies have suggested positive correlations between human consumption ofgreen tea and a lower incidence of gastric, esophageal, ovarian, pancreatic colorectalcancers. EGCG, the major polyphenol in green tea, was found in animal studies to inhibitcarcinogenesis effectively and broadly in various organs, such as the esophagus, stomach,and duodenum. Some clinical studies used oral EGCG for extended periods of time, inwhich EGCG was very well tolerated with virtually no reportable side effects. In cardiacpatients, EGCG is reported to have improved endothelial function and increased brachialartery flow-mediated dilation that paralleled the changes in plasma EGCG concentration.Numerous studies have described effects of EGCG when used in overweight and obese individuals for extended durations. Our group has recently demonstrated the ability ofEGCG to control the proliferation and induce apoptosis in human leiomyoma cells, invitroand in animal models. Our preclinical data in fibroid animal models demonstratesthat EGCG added to drinking water was able to induce a highly significant shrinkage offibroid lesions compared to untreated controls. Overall, emerging evidence suggest greentea and its extract as safe treatment for several diseases.