Cancer Treatment Centers of America

Drinking green tea to prevent cancer? Studies are mixed

blog green tea benefits

On any given day, 160 million of us fill our mugs with hot tea or pair our meals with a glass of iced tea. Half of all Americans are drinking tea, fueling its growing popularity as researchers find it may help prevent disease—including cancer.

Most studies exploring the link between tea and cancer prevention focus on green tea, which comes from the Camellia sinesis plant, the same one as the more popular black tea used for iced tea. 

Unlike green tea, the leaves of black tea may have fewer healthy antioxidants because they’re fermented. Antioxidants may prevent or delay some types of cell damage.

If you’re a green tea drinker, you’ve probably heard of the tea’s health benefits. The research on its cancer-fighting properties is promising but mixed. Here are two recent reviews of multiple studies:

  • Five cups of green tea a day may help prevent cancer and recurrent colorectal cancer, according to a research review in the Journal of Cancer Research and Clinical Oncology.
  • Green tea may reduce risk of ovarian, prostate and breast cancers, according to a research review in the Journal of the American College of Nutrition.

The second research review cited two studies, one finding that Asian American women who drink green tea had a decreased risk of breast cancer and another suggesting a lower risk of breast cancer recurrence in Japanese patients drinking at least three cups of the tea daily. The review also noted that breast cancer risk was unaffected in a larger study of more than 35,000 Japanese women.

Daniel Kellman, Clinical Director of Naturopathic Medicine at our hospital outside Atlanta, says studies involving Asians may not offer a direct parallel for Americans. Genetics could be at play, as Asians have lower rates of breast cancer but higher rates of stomach and esophageal cancer.

Since 2006, more than 50 studies have compared groups who drink green or black tea to those who do not. The results have been inconsistent, according to the National Cancer Institute, but studies have linked the teas to reduced risk of colon, breast, ovarian, prostate and lung cancers. Inconsistencies may be due to differences in preparation and consumption, methods of tea production and lifestyle factors such as physical activity and tobacco use.

Evidence suggests green tea’s anti-cancer effecs, which supports its place in your diet, Kellman says. Green tea may act in two ways:

  • By altering genetic expression: It may increase activity of the p53 “tumor suppressor gene,” increasing programmed cell death of cancer cells. 
  • By its antiangiogenic effect: It may prevent tumor-associated blood vessel formation, decreasing nutrient delivery to cancer cells.

Kellman recommends choosing organic green tea to avoid pesticides. Patients who switched from conventional green tea to organic saw a decrease in their liver enzymes. Elevated liver enzymes are associated with inflammation and cell damage.

How much green tea should you get? One 275 mg capsule of green tea extract equals two cups of green tea. Studies of large groups of people have found that those who drank eight to 12 cups of green tea daily had a lower incidence of cancer.

Cancer patients drinking green tea should be aware of possible interactions with drugs, including the blood thinner Coumadin® and the chemotherapy drug Velcade® for multiple myeloma.

Learn more about naturopathic medicine at our hospitals.