Updated May 01, 2014.
Written or reviewed by a board-certified physician. See About.com's Medical Review Board.
Question: Can Green Tea Prevent Colon Cancer?
Answer:
Green tea is purported to have many anti-cancer benefits, but can green tea prevent colon cancer? If the latest research is an indication, that's a big...maybe.
Where Does Green Tea Come From?
Green tea is believed to have originated in China about 5,000 years ago. It spread to other areas in Asia from there and then to Europe and America in the 17th and 18th centuries.
What is Green Tea
Authentic green tea is made from the Camellia sinensis plant. This same plant is used to make black and white tea, too. White tea is the least processed, with the leaves being steamed and dried. Black tea is the most processed, with leaves being withered, rolled, fermented, and roasted.
Green tea falls somewhere in the middle, with the main difference between black and green teas being that the leaves are fermented for black tea, but not for green.
Can Green Tea Prevent Colon Cancer?
Cell and animal studies suggest that green tea can:
- Cause cell death in cancer cells
- Inhibit the spread of cancer cells
- Suppress the formation and growth of human cancers
- Dampen inflammation that can lead to cancerous cell changes
- Turn on tumor suppressor genes in cells
- Reduce cell damage
- Improve cell-to-cell communication
- Regulate the cell growth cycle
- Provide cellular antioxidant protection
That's an impressive list, but cells and animal studies do not prove that green tea prevents colon cancer. They suggest that it has anti-cancer properties.
Green Tea Drinking Around the World
Several large population studies have noted that compared with people who don't drink green tea, people who regularly drink the brew have lower colon cancer risk. Most of the studies suggest that to get a colon cancer protective effect, a person needs to drink at least three to five cups (or two to three large mugs) of green tea per day.
A 2009 green tea review concluded that the research points to a protective effect of green tea against several cancer types, including colon cancer, but it is not conclusively proven that green tea prevents cancer. Several other reviews published in the past few years have more strongly suggested that green tea can prevent colon cancer, but without a controlled trial, we can't know for sure that it does.
Green Tea and Colon Cancer Clinical Trials
Fortunately, there is a clinical trial. Researchers invited 136 patients to participate in a study on green tea and colon adenomas. Adenomas are colon growths that can develop into colon cancer if not removed.
After two colonoscopies to remove adenomas, which took place one year apart, the study subjects were randomly selected to one of the following groups:
- Drink green tea daily. The green tea drinkers averaged six cups per day.
- Drink green tea and take a dietary supplement of green tea extract (GTE), which provided green tea nutrients equivalent to drinking about ten cups per day -- six cups of tea, plus the GTE.
After one year, the study subjects underwent another colonoscopy. Researchers noted:
- 31% of study participants in the green tea group developed another adenoma
- 15% of study participants in the tea plus GTE group develop another adenoma
- Compared with the green tea-only group, people in the green-tea-plus-GTE group were 51% less likely to develop an adenoma
This study found that consuming the equivalent of ten cups of green tea per day, from a combination of tea and tea supplements, can significantly reduce the risk of pre-cancerous colon growths. Unfortunately, we have no way of comparing risk between people drinking moderate amounts of green tea (six cups per day in this study) with non-green tea drinkers.
The Bottom Line on Green Tea and Colon Cancer
If you are being treated with Bortezomib (velcade) or related medications, do not drink green tea or take green tea supplements. Some research suggests that nutrients in green tea may lessen the effectiveness of these treatments.
If you are not taking these medications, you may want to give green tea a try. While not all studies show a colon cancer protective effect of green tea, the brew may help and is unlikely to cause harm.
One controlled trial suggests green tea can reduce the risk of precancerous colon growths. The equivalent of ten cups per day was consumed in this study, but population studies suggest health benefits at three to five cups per day.
If you enjoy green tea, you certainly can't go wrong drinking it, unless you are taking the medications mentioned above or are trying to avoid caffeine. Green tea does have some caffeine, though significantly less than coffee.
And keep in mind that if green tea replaces other, less healthy beverages such as soda, you'll be doing your health a favor by making the switch. If you don't like green tea, not to worry. You aren't missing out on the miracle cure of the century. Also, you can reduce your colon cancer risk in other ways, such as exercising, not smoking, and maintaining a healthy body weight.
If you like other types of tea, you may get health benefit from adding those in as well. Health experts believe black and white tea also protect against cancerous changes in cells in the body.
If you're interested in current research on green tea and colon cancer, there are clinical trials looking at green tea as an addition to conventional colon cancer treatment.
Sources:
Kumar N, Shibata D, Helm J, Coppola D, Malafa M. "Green tea polyphenols in the prevention of colon cancer."Frontiers in Bioscience 2007 12:2309-15.
Oral Green Tea Extract and Milk Thistle Extract to Colorectal Cancer Patients Undergoing Resection. National Institutes of Health. ClinicalTrials.Gov. http://clinicaltrials.gov/ct2/show/NCT01239095
Shankar S, Ganapathy S, Srivastava RK. "Green tea polyphenols: biology and therapeutic implications in cancer."Frontiers in Bioscience 2007 12:4881-99.
Shimizu M, Fukutomi Y, Ninomiya M, Nagura K, Kato T, Araki H, Suganuma M, Fujiki H, Moriwaki H. "Green tea extracts for the prevention of metachronous colorectal adenomas: a pilot study." Cancer Epidemiology Biomarkers & Prevention 2008 17:3020-25.
Yang CS, Wang X. "Green tea and cancer prevention."Nutrition and Cancer 2010 62:931-37.
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