Though often touted as a health-booster, green tea might elevate certain liver enzymes. Also, while the tea's effects often are attributed to the antioxidant effects of its polyphenols, some tea polyphenols might actually boost pro-oxidant activity, according to "Herb, Nutrient, and Drug Interactions" by Mitchell Bebel Stargrove, et al. Dosage is a factor, which means concentrated extracts pose a higher potential risk. Risk for toxicity also may be higher when green tea extract is used during fasting, notes Sloan-Kettering Memorial Cancer Center in New York. Consult a doctor before trying green tea, especially if you use medication or have liver issues or other health conditions.
Safety Rating
The U.S Pharmacopeia in 2007 classified green tea extract with a Class 2 safety rating, which requires a warning label in the substance's monograph statement, due to reports of liver damage associated with consumption of concentrated green tea extracts. However, this requirement has been deferred because the Dietary Supplements Information Expert Committee is reviewing its safety classification policy.
Liver Enzyme Changes
Animal research reveals that green tea can cause changes in liver enzymes, including the enzyme that metabolically activates heterocyclic amines, according to Roderick H. Dashwood, a principal investigator for the Oregon State University Linus Pauling Institute and professor of molecular and environmental toxicology. This liver enzyme, CYP1A2, converts these mutagens from cooked meats from an inactive form to an active form. This led to the hypothesis that rats given heterocyclic amines and green tea together might have an increased risk of colon cancer, according to Dashwood.
Expert Insight
Contrary to expectations, instead of increasing risk for colon cancer, giving rats heterocyclic amines and green tea together actually decreased risk, according to Dashwood. This might mean the possible anticancer effect of green tea is due, in part, to its effect on liver enzymes. The polyphenols in green tea might, for example, modulate phase 2 liver enzymes, which might in turn metabolize carcinogens toward inactivation, according to "Botanical Medicines," by Dennis J. McKenna, et al. Such effects might be dose-dependent. Green tea infusions at 2.5 percent of drinking water volume appear to increase just one phase 2 liver enzyme in rats, whereas infusions of 5 percent increase two phase 2 liver enzymes, McKenna notes. The 2.5 percent level approximates the concentration a human would consume when drinking tea.
Considerations
Information on green tea's liver effects remains contradictory as of 2011. On one hand, green tea appears to protect against liver tumors and protect your liver from damaging effects from toxic substances, including alcohol, notes the University of Maryland Medical Center, or UMMC. Also, if you are a man who drinks 10 cups or more of green tea, you are less likely to develop a liver disorder, note the experts at the center. The polyphenol called catechin in green tea also appears to help treat viral liver inflammation, according to UMMC. On the other hand, there are reports of liver toxicity from green tea. According to an April 2009 "European Journal of Clinical Pharmacology" scientific review, cases of liver toxicity are likely due to the polyphenol epigallocatechin gallate, better known as EGCG, or its metabolites. Under certain metabolic conditions, EGCG may lead to oxidative stress in the liver, according to lead review author G. Mazzanti. In some of the cases of toxicity, medication interactions may be a factor, according to Mazzanti. Green tea interacts with numerous medications, according to University of Maryland Medical Center.
References
- Oregon State University Linus Pauling Institute; Tea Time; Roderick H. Dashwood; May 2005
- U.S. Pharmacopeia; Update on the USP Green Tea Extract Monograph; April 2009
- University of Maryland Medical Center; Green Tea; September 2010
- "European Journal of Clinical Pharmacology"; Hepatotoxicity From Green Tea; G. Mazzanti, et al; April 2009
- "Journal of Biological Chemistry"; Epigallocatechin Gallate, a Green Tea Polyphenol, Mediates NO-Dependent Vasodilation Using Signaling Pathways in Vascular Endothelium Requiring Reactive Oxygen Species and Fyn; J.A. Kim, et al; May 2007
- "Herb, Nutrient, and Drug Interactions"; Mitchell Bebel Stargrove, et al; 2008
