TUESDAY, July 21, 2009 (HealthDay News) -- Does drinking green tea really help prevent cancer? The answer is still unclear, according to a review of 51 previous studies done over two decades.
The review, published online in The Cochrane Database of Systematic Reviews, found that green tea may offer some help against liver cancer, breast cancer and, in men, prostate cancer, but consumption may actually increase one's chances of developing urinary bladder cancer. Conflicting evidence was found in the case of gastrointestinal (esophagus, colon or pancreas) cancers, though the authors noted "limited moderate to strong evidence" of green tea protecting against lung, pancreatic and colorectal cancer."
"Despite the large number of included studies, the jury still seems to be out on the question of whether green tea can in fact prevent the development of various cancer types," lead review author Katja Boehm, a member of the Unconventional and Complementary Methods in Oncology Study Group in Nuremburg, Germany, said in a news release issued by the journal's publisher, The Cochrane Collaboration.
The researchers reviewed studies involving more than 1.6 million people in Asia, where green tea consumption is a regular habit. Boehm said that variables in how much green tea people drink and how different cancers grow makes it difficult to find a conclusive relationship about whether green tea helps prevent cancer.
"One thing is certain," she said, "Green tea consumption can never account for cancer prevention alone."
Green tea is rich in polyphenols, which include the powerful antioxidants called catechins. Though these polyphenols are in other black and oolong teas, which come from the same plant, some claim the polyphenols in green tea have unique cancer-preventing abilities that prevent cell growth.
"The substances found in green tea are certainly promising," Nagi Kumar, director of Nutrition Research at Moffitt Cancer Center in Tampa, Fla., said in the same news release. "The field now has progressed to where we [can] test the effectiveness and safety of green tea polyphenols using a drug form similar to the constituents in tea to see if we can prevent cancer progression. Time will tell."
Both researchers agreed that more thorough studies should be done on the subject and, in the meantime, drinking green tea in moderate amounts is safe, if not beneficial. Boehm said daily consumption of no more than 1,200 milliliters (just over five cups) a day is recommended.
The U.S. National Cancer Institute has more about tea and cancer prevention.