Following up on experiments that suggested green tea extracts had a preventive effect on colorectal cancer, the team set out to learn whether green tea extracts would have the same effect on colorectal adenomas, benign polyps which are a precursor to colorectal cancer.

The researchers gathered 136 patients with colorectal adenomas, removed their polyps, waited a year to make sure their colons were still clean, then fed a group of 71 of the patients doses of green tea extracts. After 12 months, 15 percent of patients in the group consuming the extracts had metachronous adenomas, compared to 31 percent of the patients not taking the extracts.

According to an abstract, the study concludes that green tea extract "is an effective supplement for the chemoprevention of metachronous colorectal adenomas."