Green tea does not protect against breast cancer. A study of data from approximately 54,000 women, published in BioMed Central's open access journal Breast Cancer Research, found no association between drinking green tea and breast cancer risk.
Motoki Iwasaki, from the National Cancer Center, Tokyo, worked with a team of researchers to carry out the study. He said, "Although in vitro and animal-based studies have suggested that green tea may have beneficial protective effects against breast cancer, results from human studies have been inconclusive. Our large-scale, population-based prospective cohort study is one of the first to include a wide range of tea intakes; women who drank green tea less than 1 cup per week to those who drank 10 or more cups per day. It found no overall association between green tea intake and the risk of breast cancer."
Tea intake was assessed by questionnaire, once at the beginning of the study and then again five years later. Cancer incidence was assessed by notification from major local hospitals in the study area and data linkage with population-based cancer registries. Approximately 12% of women drank green tea less than 1 cup per week while 27% drank 5 or more cups per day.
Speaking about the survey, Iwasaki said, "The other major strength of the present study was its prospective design, in which information was collected before the subsequent diagnosis of breast cancer, thereby avoiding the exposure recall bias inherent to case-control studies. Drinking green tea as a beverage is unlikely to reduce the risk of breast cancer regardless of green tea type and number of cups."
- Motoki Iwasaki, Manami Inoue, Shizuka Sasazuki, Norie Sawada, Taiki Yamaji, Taichi Shimazu, Walter C Willett, Shoichiro Tsugane and for the Japan Public Health Center-based Prospective Study Group (JPHC). Green tea drinking and subsequent risk of breast cancer in a population-based cohort of Japanese women. Breast Cancer Research, 2010; (in press) [link]
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