November 9, 2023 – Can green tea reduce your risk of colon cancer? It is dependent upon who – and what research – you think.
Evidence linking green tea to a lower risk of colon cancer goes each ways. Some researchers have found that drinking the favored tea poses little or no significant risks, while others point to potential advantages. Now add two more studies – one which found no reduced risk and one other that appears to strengthen the link between green tea and a lower risk of colon cancer.
Randomized controlled trials—through which some individuals are randomly assigned to drink green tea and others will not be—are considered the gold standard of medical research. Combine the outcomes of several of those studies, the considering goes, and the outcomes develop into even stronger.
The combination of random tests has up to now shown no advantage of green tea. But there could still be a profit, said lead researcher Vishal Chandel, MD, who's affiliated with Suburban Community Hospital in Norristown, Pennsylvania. It might be that there simply aren't enough randomized controlled trials yet to prove that green tea has a protective effect.
“Many, many factors contribute to the development of colorectal cancer, and one of them is diet. One thing that stood out to me was tea, because tea is consumed around the world and has shown some stronger effects in Japan and China,” Chandel said.
Comparison of a whole bunch of individuals
Chandel and colleagues found three randomized controlled trials that examined the association between green tea and the danger of colorectal cancer. Collectively, the information included 451 individuals with colorectal cancer and 460 additional people without cancer, forming a control or comparison group.
They found that green tea consumption didn't reduce the danger of colon cancer in a statistically significant way.
“There are only three randomized controlled trials in the world on green tea and colorectal cancer,” Chandel said. “We actually need more. If we had seven, eight or ten… I'm very sure we'll have a much stronger association with saying that green tea can have a positive effect.”
Comparison of thousands of people
Chandel and colleagues also conducted another study in which they examined less rigorous evidence – 10 cohort studies and 15 prospective case-control studies. These studies included 198,488 cancer cases and 581,556 controls. This time they found a stronger link between green tea and a reduced risk of colon cancer.
The “results of the meta-analysis suggest a lower tendency to develop colorectal cancer when consuming green tea, with the risk of colorectal cancer being more pronounced in Asia than in America or Europe,” the authors note. “Although epidemiological data are currently insufficient to conclude that green tea may have a protective effect in humans.”
Chandel presented the results of both studies in Vancouver, Canada, at the annual scientific meeting of the American College of Gastroenterology (ACG).
Why green tea?
Chandel said he studied colorectal cancer because it is the third most commonly diagnosed cancer worldwide, accounting for about 10% of all new cancer cases in 2020, according to the World Health Organization Global Cancer Observatory Data. It is also the second most common cause of cancer death worldwide after lung cancer.
Green tea contains a high proportion of polyphenols, the so-called catechins. The main catechin in green tea that is believed to have anticancer effects is epigallocatechin-3-gallate (EGCG). “EGCG has been shown to inhibit or prevent colorectal cancer in some studies,” Chandel said.
EGCG is found in greater amounts in green tea than in black tea or oolong tea because green tea is made from non-fermented, non-oxidized tea leaves.
It's difficult to read the tea leaves
These studies “add to the literature, which stays undefined regarding the role of green tea in reducing the danger of colorectal cancer,” said Catherine Eng, MD, a spokeswoman for the American Society of Clinical Oncology, when asked for comment.
Although combining three studies did not show significant benefit, when looking at larger numbers of studies there was success in some populations, said Eng, co-director of gastrointestinal oncology and chair of surgical and medical oncology at Vanderbilt-Ingram Cancer Center in Nashville .
“A possible good thing about green tea in reducing the danger of colorectal cancer was present in the Asian cases, but was not found to be statistically significant within the European or US studies,” she said. “Currently, the role of dietary green tea consumption in reducing the risk of colorectal cancer is not well understood and requires further study.”