Although some research has suggested that drinking green tea might help protect women from breast cancer, a new, large Japanese study comes to a different conclusion.
"We found no overall association between green tea intake and the risk of breast cancer among Japanese women who have habitually drunk green tea," said lead researcher Dr Motoki Iwasaki, from the Epidemiology and Prevention Division at the Research Center for Cancer Prevention and Screening of the National Cancer Center in Tokyo.
"Our findings suggest that green tea intake within a usual drinking habit is unlikely to reduce the risk of breast cancer," he said.
The report is published in the journal Breast Cancer Research.
For the study, Iwasaki's team collected data on 53,793 women who were surveyed between 1995 and 1998. As part of the survey, the women were asked how much green tea they drank.
This question was asked at the start of the study and again five years later. During the second survey, the researchers asked about two different types of green tea, Sencha and Bancha/Genmaicha.
Among the women, 12% drank less than one cup of green tea a week, while 27% drank five or more cups a day, the researchers found. The study also included women who drank 10 or more cups a day.
Over almost 14 years of follow-up, 350 women developed breast cancer, but the researchers found no association between drinking green tea and the risk for developing breast cancer.
In the study, Iwasaki noted that one strength of the research was its prospective design, so that the information was collected before the diagnosis of breast cancer, "thereby avoiding the exposure recall bias inherent to case-control studies."
Dr Stephanie Bernik, a breast cancer surgeon at Lenox Hill Hospital in New York City, said that "it's hard to say that there is no benefit from green tea overall, certainly. Maybe there is no benefit for breast cancer specifically."
Bernik noted that many women are interested in alternative medicine when Western medicine doesn't have the answers.
"We are always looking to learn more about how to improve the outcome of breast cancer and how to reduce the incidence of breast cancer," she said. Women are definitely interested in how they can have a healthier lifestyle."
Jennifer J. Hu, a professor of epidemiology and public health at the University of Miami School of Medicine's Sylvester Comprehensive Cancer Center, added that the problem with population-based studies is that when you try to look at one single factor you may not be taking into account other risk factors that can influence the result.
"Also, just by drinking green tea you don't get enough of the [possible cancer-fighting ingredient] to make much of a difference," she said.
Based on these problems, Hu doesn't think this study answers the question of whether or not green tea might help guard against breast cancer.