Can Green Tea Prevent Colon Cancer?

A mug of green tea.
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Authentic green tea is made from the Camellia sinensis plant. This same plant is used to make black and white tea, too. The difference is in the processing. To make green tea, leaves are dried, rolled and roasted.

Green Tea and 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

Does Green Tea Prevent Colon Cancer?

Several large population studies have noted that people who regularly drink green tea have a lower incidence of colon cancer compared with those who don't drink the brew. Many of the studies suggest that a person needs to drink at least three to five cups of green tea per day to get that protective effect.

A 2009 green tea review concluded that green tea protects against several types of cancer, including colon cancer, but that's not the same as concluding that it prevents cancer.

Green Tea and Colon Cancer Clinical Trial

In a 2008 clinical trial published in Cancer Epidemiology Biomarkers & Prevention, researchers studied the effect of green tea and/or green tea extract on cancer recurrence in people who had had surgery for adenomas (colon growths that can develop into colon cancer if not removed).

Post-surgery, 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, significantly reduced the risk of precancerous colon growths.

Another study suggested 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.

Medication Interactions

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.

Bottom Line

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, although much less than coffee (if you're drinking several cups per day, though, it adds up).

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. Black and white tea may also protect against cancerous changes in cells in the body. Also, you can reduce your colon cancer risk in other ways, such as exercising, not smoking, and maintaining a healthy body weight.

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