Eating foods rich in isoflavones may reduce the risk of breast cancer, especially in postmenopausal women, suggests Japanese research. Frequent consumption of soy-rich miso soup was found to be particularly effective.
Although isoflavones, such as those found in soy, have been shown to inhibit breast cancer in laboratory studies, researchers have found associations between consumption of isoflavone-containing foods and breast cancer risk to be inconsistent.
Led by Seiichiro Yamamoto, researchers from the National Cancer Center Research Institute in Japan evaluated the relationship between isoflavone consumption and breast cancer risk among women as part of the Japan Public Health Center-based prospective study on cancer and cardiovascular diseases (JPHC Study).
The study concentrated on the incidence of breast cancer in relation to consumption of soy foods, miso soup - a soy-filled staple of Japanese cuisine - and overall estimated isoflavone intake.
The study began in 1990, when nearly 22,000 Japanese female residents, aged 40-59 years, from four public health centre areas completed a self-administered questionnaire, which included items about the frequency of soy consumption. Ten years later 179 of these women had been diagnosed with breast cancer.
The scientists found that while soyfoods alone did not have a significant effect, both consumption of miso soup and overall isoflavone intake reduced the risk of breast cancer.
The participants were divided into four categories according to isoflavone intake. On comparison with those in the lowest quartile of isoflavone intake, the adjusted reduced risk for breast cancer for women in the second, third, and highest quartiles were 0.76, 0.90 and 0.46 respectively.
In addition the researchers reported that the inverse association was found to be stronger in postmenopausal women.
These associations did not change substantially after adjustment for reproductive history, family history, smoking, and other dietary factors, according to the researchers.