Review and Perspective on the Composition and Safety of Green Tea Extracts

The growing body of evidence regarding the putative health benefits of green tea (Camellia sinensis), including reduced risk of cancer and cardiovascular disease, has led to an increase in the consumption of brewed green tea and the formulation of green tea extracts (GTE) into a variety of food and beverage products and food supplements. The principal bioactive ingredients in green tea beverages and GTE are polyphenols, particularly the flavan-3-ols, which have been shown to act on antioxidant, anti-inflammatory, glucoregulatory, and cell signaling pathways. Some experimental evidence and case reports suggest the use of green tea and GTE is associated with the potential for inducing liver injury. The ability to extrapolate findings from in vitro and animal model studies is always limited and the available results on green tea- and GTE-induced liver injury in humans have presented clinical and regulatory challenges due to the difficulty of demonstrating a causal relationship between intake and harm. Attention to the risk for hepatotoxicity has largely been focused on GTE. Existing data are insufficient to identify the causative agent in the preparation or composition of GTE or its dose or duration of use as well as nutrigenetic, medical, and other factors that may contribute to the risk of hepatotoxicity. Responses by different government regulatory agencies regarding the safety of GTE are inconsistent with one another, including the dosage and derivation of its bioactives from aqueous versus hydro-alcoholic extracts. Restrictions on the production of GTE limit the application of innovative extraction technologies that may improve the efficiency, quality, and cost-effectiveness of production and minimize the presence of endogenous or contaminant heavy metals as well as mycotoxins, pesticides, and other unwanted constituents. The objective of this review is to characterize the phytochemical profile of green tea and GTE, provide an updated description of the methods that could be used to extract green tea constituents, and discuss recent considerations on the potential for harm from consumption of GTE and products containing GTE.