Green tea and cancer in humans: a review of the literature.

Researchers have investigated green tea as a potential protectant against cancer. This review focuses on studies of green tea in humans. Green tea contains polyphenols, chemicals that act as powerful antioxidants. Epidemiological and human studies have shown varying results. Thirty-one human studies and four reviews were examined. Among five studies reporting on colon cancer, three found an inverse association and one reported a positive association. For rectal cancer, only one of four studies reported an inverse association; increased risks were seen in two of the studies. An inverse association is suggested for urinary bladder cancer in two of two studies. Of 10 studies examining the association of green tea and stomach cancer, 6 suggest an inverse and 3 a positive association. The most comprehensive of these studies supports an inverse association of green tea and stomach cancer. Pancreatic cancer studies hint at an inverse association in two of three studies. A strong inverse effect was found with green tea and esophageal cancer. Lung cancer studies have shown an inverse effect with Okinawan tea, yet tentatively increased risk was shown in another study. Although human studies have their limitations, the research has warranted a further look into the effects of green tea and cancer.