Motoki Iwasaki, from the National Cancer Center in Tokyo, Japan, and colleagues analyzed data from the Japan Public Health Center-based Prospective Study. They looked at nearly 54,000 women who were questioned about their daily green tea intake. About 12% of women drank less than one cup of green tea per week, and 27% drank five or more cups every day. During the study period, there were 581 new cases of breast cancer diagnosed.
The researchers found that breast cancer risk did not differ between women who drank the most green tea and women who drank the least. The findings, published in the latest issue of Breast Cancer Research, call into question the widely held notion that drinking green tea is a potential way to reduce the risk for breast cancer.
Iwasaki said there were several strengths to the study design, including the number of women surveyed and the wide variation of the participants’ tea intake.
“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,” Iwasaki says in a statement. “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. Drinking green tea as a beverage is unlikely to reduce the risk of breast cancer, regardless of green tea type and number of cups.”
What Animal Studies Have Found
Animal studies have suggested that the polyphenols and antioxidants found in green tea may be protective against cancer, including breast cancer. A study presented in 2008 had suggested that the antioxidant epigallocatechin-3-gallate, also known as EGCG and is abundant in green tea, could slow breast tumor growth in mice. A more recent study published this year in BioMed Central Cancer also suggested that EGCG found in green tea decreased breast cancer cell growth in mice. However, these kinds of outcomes have not been observed in people.
Compared with Western countries, breast cancer rates are lower in many Asian countries where green tea is a popular everyday drink. Breast cancer is one of the most common cancers among American women. According to the CDC, data from 2006 shows that 191,410 women were diagnosed with breast cancer that year and 40,820 women died from the disease.