Green tea can be dangerous for some people, Israeli study concludes

Tea is the second-most popular beverage in the world, but if you drink the green variety, you may want to pause before downing your next cup.

A new peer-reviewed study published by Israeli and Canadian researchers warns that green tea can cause severe liver damage in some individuals. At this point, there is no way to know exactly who is predisposed to this danger, so green tea lovers need to be aware of possible adverse effects.

According to the study’s lead author, Prof. Stephen Malnick, head of an internal medicine department at Kaplan Medical Center in Rehovot, green tea deserves credit for many significant benefits it has provided humans since ancient times.

“It’s connected with preventing metabolic syndrome [a combination of diabetes, high blood pressure, and obesity] and promoting weight loss. It has beneficial effects on the heart,” Malnick said.

The problem is that green tea is also the number one cause of herbal-induced liver injury (HILI). Although uncommon — only 100 cases worldwide in the medical literature — HILI can be serious and quickly lead to acute liver failure, or at the very least damage that takes months or years to reverse.

Malnick, who is also on the faculty of the Hebrew University Medical School, said that the study published in GastroHep is timely as the use of green tea has skyrocketed in the last few years. People not only drink it but also consume it through other products such as nutritional supplements.

“There’s an estimate that by the end of this decade, there will be about a $27 billion market for green tea in the United States. And green tea is not just one entity. It has lots of different combinations of materials, some of it imported from places like India, and may actually even contain heavy metals, which is dangerous in itself,” Malnick said.

The study analyzed nearly 60 peer-reviewed articles on green tea and other herbs and hepatotoxicity. It found that a person’s response to green tea is idiosyncratic. It is impossible to predict who is likely to become sick from it, or how much green tea is too much for those people. This doesn’t mean that one should not enjoy it, it just means that one should be aware.

Malnick said that it is critical to know the signs of HILI and to seek medical attention should they occur. These include what Malnick termed “suspicious symptoms” including weakness, loss of appetite, dark urine, pale stools, and pruritis (itchy skin). Jaundice, or yellowing of the skin or whites of the eyes, is also something to look out for.

According to Malnick, the results of the study are as important for doctors as they are for green tea drinkers. He said that physicians should add questions about green tea consumption when patients come into the clinic or hospital.

He recalled the case of a patient with serious liver damage he treated. She had been fully investigated at another hospital, had been asked repeatedly about medications she was taking, and even had a liver biopsy. No one could figure out why her liver was failing.

“When I was doing rounds with medical students, I asked this patient about green tea. It turned out that indeed she did take green tea. She’s okay now, but it took a year and a half of steroid treatment,” Malnick said.