Nonclinical and Clinical Safety Studies on Green Tea Extracts

Green tea, one of the most popular beverages in the world, has been reported to show beneficial effects in prevention and treatment of diseases. Although green tea extract (GTE) is believed to have pharmacological effects on the reduction of body lipid and blood cholesterol levels, regulatory agencies in France and Spain suspended market authorization of a weight-loss product containing GTE due to hepatotoxicity concerns. Although the pathogenesis of the liver damage caused by GTE is said to be unknown, epigallocatechin-3-gallate (EGCG) has been identified as the main component in the GTE probable responsible for hepatotoxicity. The present review is aimed to provide a comprehensive overview of safety from nonclinical and clinical studies on GTE as dietary supplements. Peer-reviewed articles on nonclinical and clinical safety of GTE from 2005 to 2017 were acquired from Pub Med, Scopus, Science Direct, and SCI Finder. Based on repeated dose toxicity tests, the no-observed-adverse-effect levels (NOAEL) of GTE, EGCG and catechin fraction were estimated to be more than 500, 67.8, and 500 mg/kg/day, respectively. Several clinical trials showed the hepatotoxicity risk associated with GTE is limited. For the safety management of dietary supplements containing GTE, it is needed to set up the specification on the upper limit of EGCG content. Furthermore, the warning label on the GTE supplement should be mandatory to inform the consumers of using the product with food intake and paying closer attention to ingestion of the GTE preparations in patients with high susceptibility to liver damage or liver transplantation.