In Asia, the region where soy consumption is the highest, breast cancer incidence happens to be relatively lower in comparison with Western countries. Therefore soy has come to the attention of researchers as an ingredient that may help prevent the development of breast cancer. Because soy isoflavones are structurally similar to estrogen, they can weakly bind to estrogen receptors when the local estrogen concentration is low. As a result, many studies have demonstrated the breast cancer prevention effects of soy isoflavones. However, the potential estrogenic effect of soy isoflavones raised the concern whether soy isoflavones were safe to be consumed by breast cancer patients or women at high risk for breast cancer.
The Osteoporosis Prevention Using Soy (OPUS) study examined the correlation between different doses of an isoflavone supplement and mammographic density in a 2-year long clinical trial designed to document the safety, efficacy and optimal dosage of soy isoflavones to prevent bone loss after menopause.
Taking an isoflavone supplement did not influence mammographic breast density in postmenopausal women. Stratification by age and BMI also did not indicate an effect of the treatment for any subgroup of women.
These results show that a long-term intake of soy germ isoflavones in high concentrations do not have a negative influence on breast health.