Experimental studies indicate the chemopreventive properties of green tea extract (GTE) on colorectal cancer, while epidemiologically, green tea consumption of more than ten cups daily is associated with reduced colorectal cancer risk.

A Japanese team has conducted a randomised trial to determine the preventive effect of GTE supplements on colorectal adenomas. They recruited 136 patients, removed their colorectal adenomas by endoscopic polypectomy, and one year later confirmed their colons polyp-free by colonoscopy.

Patients were then randomised into two groups, while maintaining their existing green tea consumption: one group received supplementation with 1.5 g GTE (equivalent to 6 cups) per day for 12 months, while the other group of control patients did not receive supplementation. Follow-up colonoscopy was conducted 12 months later.

The incidence of adenomas at the end-point colonoscopy was 31% in the control group compared with 15% in the GTE group. The authors conclude that GTE is an effective supplement for the chemoprevention of colorectal adenomas. (Green tea extracts for the prevention of metachronous colorectal adenomas: a pilot study. Cancer Epidemiol Biomarkers Prev. 2008 Nov;17(11):3020-5).