Green tea extract is generally considered safe when consumed in moderate amounts. However, some people may be more sensitive to the effects of green tea extract and may experience adverse reactions when using it.
Some research suggests that people with certain genetic variations may be more likely to experience liver damage when taking high doses of green tea extract. It is important to speak with a healthcare provider before taking green tea extract, especially if you have liver problems or are taking other medications that may affect the liver. It is also a good idea to follow the recommended dosage instructions on the product label and to not exceed the recommended dose.
A new study found that early signs of liver damage from high-dose green tea extract were somewhat predicted by one genotype variation and strongly predicted by another. Long-term consumption of high-dose green tea extract may offer some protection against cancer, cardiovascular disease, obesity, and type 2 diabetes, but it may also cause liver damage in a small percentage of the population.
Who is in danger? The first solid clue comes from Rutgers research, which was published in The Journal of Dietary Supplements: two genetic variants that predict some of the risk.Hamed Samavat
“Learning to predict who will suffer liver damage is potentially important because there is growing evidence that high-dose green tea extract may have significant health benefits for those who can safely take it,” said Hamed Samavat, the study’s senior author and an assistant professor of nutrition sciences at the Rutgers School of Health Professions.
Using data from the Minnesota Green Tea Trial, a large study of green tea’s effect on breast cancer, the researchers looked to see if people with certain genetic variations were more likely than others to show signs of liver stress after consuming 843 milligrams per day of the primary antioxidant in green tea, a catechin called epigallocatechin gallate (EGCG).
Researchers led by Laura Acosta, then a doctoral student, now a graduate, selected two genetic variations in question because each controls the synthesis of an enzyme that breaks EGCG down. They selected the Minnesota Green Tea Trial because it was a large, well-designed study of a unique population. The year-long, placebo-controlled trial included more than 1,000 postmenopausal women and collected data at 3, 6, 9 and 12 months.
Early signs of liver damage were slightly more common than normal in women with one variation in the catechol-O-methyltransferase (COMT) genotype and strongly predicted by a variation in the uridine 5′-diphospho-glucuronosyltransferase 1A4 (UGT1A4) genotype, according to a study.
After nine months of taking the green tea supplement, participants with the high-risk UGT1A4 genotype saw an increase in the enzyme that indicates liver stress of nearly 80%, while those with the low-risk genotype saw an increase of 30%.
“We’re still a long way from knowing who can safely take high-dose green tea extract,” Samavat said, noting that the risk of liver toxicity is only associated with high levels of green tea supplements, not with drinking green tea or even taking lower doses of green tea extract. “Variations in this single genotype do not fully explain the differences in liver enzyme changes among study participants. The full explanation is likely to include a number of different genetic variations as well as a number of non-genetic factors.”
“However,” Samavat continued, “we believe we have identified an important piece of the puzzle and taken a step toward predicting who can safely enjoy any health benefits that high-dose green tea extract provides.”