Review supports safety of green tea extracts

By Hank Schultz

- Last updated on GMT


Related tags Green tea functional beverage beverage

A recent systematic review of clinical trials using green tea extract underscores the ingredient’s overall safety, despite some recent associations with liver damage.

Green tea extract has come under fire in recent years for its association with liver injuries.  A supplement called SlimQuick, which lists green tea extract as one of its ingredients, has been associated with several cases of severe liver injury​, including one that required a liver transplant.  The government of Norway also recently warned about the ingredient’s hepatotoxicity potential​.

Green tea as a beverage has been consumed safely for thousands of years.  More recently ingredient developers have been extracting catechins of interest, most notably epigallocatechin gallate, or ECGC, using a variety of solvents and other extraction methods.  It is the consumption of these concentrated green tea polyphenols, which includes catechins, that concerns hepatologists.

Review looks at 34 studies

The open-source systematic review, funded by the Japan Life Sciences Institute and published in the European Journal of Clincal Nutrition, looked at more than 500 studies that mentioned green tea or green tea extract, of which 34 met the criteria for inclusion.  Most of these were efficacy studies, with six looking specifically at safety.  In 10 of the studies the subjects were healthy, seven studies looked at obese subjects, five dealt with cancer patients and the subjects in ther remaining 12 studies fit into the “other” category.  Of the 1,405 subjects in the treatment groups of these studies, only 0.5% of them showed markers of mild liver stress with only a single case of more serious liver damage that called for cessation of treatment. 

“Most of the RCTs selected reported no liver-related adverse events in either intervention or control groups. The few events reported in intervention groups were elevations of liver enzymes such as ALT or ALP. No serious adverse events were reported; most were mild, but one severe adverse event was reported, leading to the discontinuation of intervention. None of the events were judged to have a definite causal relationship to green tea intake,”​ the authors wrote.

Experts on adverse events and on herbal ingredients said the results are a boost for an embattled ingredient.  Cases of liver injury associated with supplement use that result in hospitalizations and/or lawsuits are often difficult to sort through because of myriad confounding factors such as conditions of use and the underlying health of the subject. Extracting data from controlled trials is a better way to get a balanced view of an ingredient’s safety, they said.

Strong endorsement for green tea safety

tea plantations
Image © iStockPhoto

“I think it’s pretty positive for green tea,”​ said Rick Kingston, PharmD, who is a clinical professor of pharmacy at the University of Minnesota.  Kingston is also the president, regulatory and scientific affairs at SafetyCall International​, a consultancy that helps companies deal with adverse events, managing recalls and other needs.

“Only four of the studies showed liver events, but the authors didn’t say what the numbers were of the liver enzymes in these trials. I went back and looked at the actual studies they referenced and all but one were really minor elevations of these transanimases,” ​Kingston told NutraIngredients-USA.

“This is a strong paper that suggests the relative safety of green tea extracts despite the fact that there have been case reports,” ​said Mark Blumenthal, executive director of the American Botanical Council.

Kingston said that such minor elevations can often be seen during course of treatment with pharmaceuticals, such as statins.  If a patient were to show elevations of the magnitude referenced in the green tea review, it is common to “treat through it,” ​or "adjust the dose," ​Kingston said.  In other words, to monitor the patient and continue to administer the statins and wait for the liver enzymes to fall back into the normal range, which is what usually occurs.

Kingston said this review underscores the validity of the approach that many dietary supplement advocates take, that is to look at the adverse events in the universe of overall usage.

“How many millions of servings of individual products do we have out there and adverse events are so rare.  And another thing that we see in populations that are involved with weight reduction, they have a lot of comorbid effects. They completely change their diet and their lifestyle and they can have things such as intense trauma from exercising,”​ he said.

Fasting with catechins

Blumenthal said it is important to maintain the distinction between green tea and extracted products.  And he also said that the products featuring green tea extracts often also contain other herbs, which is a potential confounding factor.

“Green tea as a beverage is an infusion and that’s different from an extract with a relatively high concentration of catechins. There have been no reports of liver injury associated with green tea. In fact the evidence suggests that it may be hepatoprotective,”​ he said.

In the case of liver injury associated with supplements containing extracts concentrated for their EGCG content, Blumenthal said there are several things possibly at work.

“One speculative reason is that these extracts are used in products marketed for weight loss and in that case the catechins often hit the liver when it is in a fasting state when it might be more susceptible.  Another speculative reason has to do with solvents.  Many of these extracts are often made with ethanol, common grain alcohol.  But there is hexane and some other solvents that might be used,”​ he said.

Source:European Journal of Clinical Nutrition
“Liver-related safety assessment of green tea extracts in humans: a systematic review of randomized controlled trials”
2016 May 18. doi: 10.1038/ejcn.2016.78. [Epub ahead of print]
Authors: Isomura T et al

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