Health Experts Advise: Avoid Green Tea Once For All

Green Tea

Introduction

Green tea is a popular and commonly consumed drink and its extract is found in many herbal and dietary supplements (HDS). Green tea extract and, more rarely, ingestion of large amounts of green tea have been implicated in cases of clinically apparent acute liver injury, including instances of acute liver failure and either need for urgent liver transplantation or death.

Background

Both green tea and black tea are produced from the leaves of the Chinese tea tree Camellia sinensis. Green tea, unlike black tea, is unfermented, which helps to preserve its antioxidant polyphenolic catechols. Green tea has long been believed to have health-restoring properties and its ingredients have antioxidant activity. For this reason, extracts of green tea have been used as an herbal medication alone and in combination with other herbals and dietary supplements which are purported to improve health, prevent cancer and heart disease, decrease serum lipid levels, promote weight loss, decrease periodontal disease and even treat clostridial diarrhoea. 

Listed in more than 100 over-the-counter herbal preparations: Green tea extract (GTE) is listed in more than 100 over-the-counter herbal preparations but is not proven for any specific medical indication and is not regulated in regards to efficacy and safety by the FDA. The multiple polyphenols in green tea are believed to be the active components responsible for its purported chemoprotective, antiproliferative and antioxidant properties. The mechanism by which green tea may have such effects has not been elucidated. Human clinical studies demonstrate that single doses of up to 1.6 grams of green tea extract are well tolerated. The maximum tolerated dose in humans is reported to be 9.9 grams per day; a dose equivalent to 24 cups of green tea. Side effects of high doses of green tea extract are usually mild and include headache, dizziness and nausea. The safety and tolerability of long-term use of green tea extracts have not been well defined.

Hepatotoxicity

Drinking green tea has not been associated with liver injury or serum aminotransferase elevations; indeed, cross-sectional studies suggest that regular use of green tea is associated with lower serum ALT and AST values. Nevertheless, case series and a systematic review by the United States Pharmacopeia have raised the issue of the potential for GTE to cause hepatotoxicity. In a large prospective study of GTE in postmenopausal women at risk of breast cancer, GTE was associated with ALT elevations in 6.7% of patients compared to 0.7% of controls. In these studies, clinically apparent liver injury was not observed, but the extract was quickly discontinued in patients with ALT elevations. Restarting GTE in a proportion of patients was followed by rapid recurrence of ALT elevations that resolved again with stopping.

Liver injury attributed to GTE: The prevalence of green tea extract-induced acute liver injury with symptoms of jaundice is not known, but but is undoubtedly low in comparison to the wide-scale use of these products. Nevertheless, more than 100 instances of clinically apparent liver injury attributed to GTE have been reported in the literature.

Fatal instances of acute liver failure: Liver injury typically arises within one to six months of starting the product but longer and shorter latencies (particularly with reexposure) have been reported. The majority of cases present with an acute hepatitis-like syndrome and a markedly hepatocellular pattern of serum enzyme elevations. Most patients recover rapidly upon stopping the extract or HDS, although fatal instances of acute liver failure have been described. Biopsy findings show necrosis.

Inputs Courtesy: National Library of Medicine

National Center for Biotechnology Information