Soy, isoflavones, and breast cancer risk in Japan

Author: Seiichiro Yamamoto et al.
Publication: Journal of the National Cancer Institute, Vol. 95, No. 12, 906-913, June 18, 2003.

Laboratory tests on rats have have shown that soy isoflavones inhibit breast cancer. The associations between consumption of foods rich in isoflavones and breast cancer risk have been inconsistent in epidemiologic studies.

The purpose of this study was to determine the relationship between isoflavones consumption and breast cancer risk among women in the Japan Public Health Center-Based Prospective Study on Cancer and Cardiovascular Diseases.

A questionnaire was completed in 1990 by 21 852 Japanese female residents (aged 40-59 years) The questionnaire included items about the frequency of soy consumption. After 9 years 179 women were diagnosed with breast cancer. The correlation was calculated between the development of breast cancer and the consumption of miso soup, soyfoods and calculated isoflavones.

The consumption of miso soup and isoflavones, but not of soyfoods, was inversely associated with the development of breast cancer. This inverse association was stronger in postmenopausal women. It can be concluded that frequent miso soup and isoflavone consumption was associated with a reduced risk of breast cancer.