Researchers investigating the association between soy food intake and breast cancer outcomes among survivors found that soy food consumption did not increase the risk of cancer recurrence or death among survivors of breast cancer.
The research was part of a multi-national collaborative study, the After Breast Cancer Pooling Project, which involved over 16,000 women between the ages of 20 and 83 years who had invasive primary breast cancer.
The researchers assessed the intake of soy isoflavones among the women after breast cancer diagnosis using food frequency questionnaires. Breast cancer outcomes were assessed, on average, nine years after cancer diagnosis.
Women in the highest intake category of more than 23 mg of isoflavones per day had a 9 percent reduced risk of mortality and a 15 percent reduced risk for recurrence, compared to those who had the lowest intake level. The average daily soy isoflavone intake among U.S. women was 3.2 mg; however, in a group of women in China, the amount was significantly higher at 45.9 mg.
The study appears to ease concerns about the safety of soy food for women with breast cancer because soy foods contain large amounts of isoflavones that are known to bind to estrogen receptors and have both estrogen-like and anti-estrogenic effects. One concern was that isoflavones might increase the risk of cancer recurrence among breast cancer patients because they have low estrogen levels due to cancer treatment. Another issue in question was whether isoflavones interfere with tamoxifen treatment as they both bind to estrogen receptors.
So, for now it appears women with a history of breast cancer can enjoy soy.
American Association for Cancer Research