THURSDAY, Nov. 5 (HealthDay News) -- A new study appears to add to growing evidence that green tea might help protect against cancer.

U.S. researchers gave 41 volunteers with pre-malignant mouth lesions green tea extract for three months at doses of 500 milligrams per meter squared (mg/m2), 750 mg/m2 or 1,000 mg/m2. The extract was taken by mouth. Other participants took a placebo.

The study found that about 59 percent of people taking the highest dose of the green tea extract showed a clinical response, compared with 18 percent of those who took a placebo. The researchers also noted a trend toward improvement in certain biomarkers that could predict cancer development.

During the study period of about 28 months, 15 people developed oral cancer. People who took the green tea extract and those who didn't were equally likely to develop the cancer. However, people who had mild to moderate dysplasia, or abnormal cell growth, at the start of the study took longer to develop oral cancer if they took the green tea extract.

Study author Dr. Vassiliki Papadimitrakopoulo, a professor in the department of thoracic/head and neck medical oncology at the University of Texas M.D. Anderson Cancer Center, said the findings were encouraging but did not provide definitive proof that green tea can prevent cancer.

"This is a phase 2 study with a very limited number of patients who took what would be the equivalent of drinking eight to 10 cups of green tea every single day. We cannot with certainty claim prevention benefits from a trial of this size," Papadimitrakopoulo said in a news release from the American Association for Cancer Research.

"The goal of this kind of research is to determine whether or not these supplements have long-term prevention effects," Papadimitrakopoulo noted. "More research, including studies in which individuals at high risk are exposed to these supplements for longer time periods, is still needed to answer that sort of question."

The findings were released online in advance of publication in the November print issue of the journal Cancer Prevention Research.

More information

The U.S. National Center for Complementary and Alternative Medicine has more about green tea.