Jury Still Out on Whether Green Tea Lowers Colon Cancer Risk

Can green tea lower your risk of colorectal cancer? It depends on who — and what research — you believe.

Evidence that links green tea and a lower risk of colorectal cancer goes both ways. Some researchers have found little or no significant risk from drinking the popular tea, while others point to a potential benefit. Now add two more studies — one that found no reduced risk and another that seems to strengthen the link between green tea and a lower risk of colon cancer.

Randomized controlled trials — where some people get randomly assigned to drink green tea and others do not — are considered the gold standard of medical research. Combine the findings from several of these trials, the thinking goes, and the findings get even stronger.

Combining random trials so far shows no advantage from green tea. But there may still be a benefit, said lead researcher Vishal Chandel, MD, who is affiliated with Suburban Community Hospital in Norristown, PA. It could be that there are just not enough randomized controlled trials yet to show green tea has a protective effect.

"Many, many factors contribute to colorectal cancer, and one of them is diet. One thing which struck me was tea, because tea is something that people consume all over the world, and it has shown some stronger effects in Japan and in China," said Chandel.

Comparing Hundreds of People

Chandel and colleagues found three randomized controlled trials that looked at the link between green tea and colorectal cancer risk. Combined, the data included 451 people with colorectal cancer and 460 others without cancer who made up a control, or comparison, group.

They found green tea consumption did not reduce the risk of colorectal cancer in a statically significant way.

"There are only three randomized controlled trials from anywhere concerning green tea and colon cancer," Chandel said. "We really need more. If we had seven, eight, or 10… I'm very positive we will have a much stronger association to say that green tea can have a positive effect."

Comparing Thousands of People

Chandel and colleagues also performed another study where they looked at 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 colorectal cancer.

The "meta-analysis results indicate a lower tendency to develop colorectal cancer with green tea consumption, with reduced risk of colorectal cancer more pronounced in Asia than America or Europe," the authors note. "Although there is insufficient epidemiological data to conclude at present that green tea can have protective effects in human beings."

Chandel presented the findings of both studies in Vancouver, Canada, at the American College of Gastroenterology (ACG) Annual Scientific Meeting.

Why Green Tea?

Chandel said he studied colorectal cancer because it is the third most diagnosed cancer worldwide, accounting for about 10% of all new cancer cases in 2020, according to the World Health Organization's Global Cancer Observatory data. It is also a common cause of cancer death globally, second only to lung cancer.

Green tea contains high level of polyphenols known as catechins. The main catechin in green tea believed to provide cancer protective effects is epigallocatechin-3 gallate (EGCG). EGCG "has been shown in some studies to inhibit or prevent colon cancer," Chandel said.

EGCG is present in higher amounts in green tea, compared to black or oolong tea, because green tea is made from unfermented, unoxidized tea leaves.

Difficult to Read the Tea Leaves

These studies "add to the literature, which remains undefined regarding the role of green tea in reducing the risk of colorectal cancer," Catherine Eng, MD, a spokesperson for the American Society of Clinical Oncology, said when asked to comment.

Although combining three trials did not reveal a significant benefit, looking at a greater number of studies did in some populations, said Eng, co-director of gastrointestinal oncology and chair of surgical and medical oncology at Vanderbilt-Ingram Cancer Center in Nashville.

"Potential benefit for green tea in reducing the risk of colorectal cancer was noted in the Asian cases but was not found to be statistically significant in the European or U.S. studies," she said. "Currently, the role of dietary consumption of green tea on reducing the risk of colorectal cancer is not well established and requires further investigation."

Sources:

American College of Gastroenterology (ACG) 2023 Annual Scientific Meeting, Oct. 20-25, 2023, Vancouver, Canada.

Vishal Chandel, MD, Suburban Community Hospital, Norristown, PA.

Catherine Eng, MD, spokesperson, American Society of Clinical Oncology; co-director of gastrointestinal oncology, chair of surgical and medical oncology, Vanderbilt-Ingram Cancer Center, Nashville.

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