Current estimates indicate that there are more than 2.9 million breast cancer survivors in the United States and more than 5 million worldwide. Breast cancer patients often have acute estrogen deprivation, due to premature ovarian failure following adjuvant chemotherapy, which increases risk of rapid bone loss and fracture. Additionally, anti-estrogenic endocrine therapies contribute to bone health issues; aromatase inhibitors exert negative effects on bone health due to estrogen depletion, and tamoxifen negatively affects BMD in premenopausal women.
In this cross-sectional study, the relationship between isoflavone intake and BMD was examined in a subset of participants (N=1,587) from the Shanghai Breast Cancer Survival Study (SBCSS). Women were divided into quartiles according to their isoflavone intake with women in the first intake quartile consuming less than 28.96 mg/d while those in the fourth quartile consumed more than 62.64 mg/d. When all women were included in the analysis, the odds ratio for osteoporosis/osteopenia (based on T score for proximal forearm BMD) for women in the fourth quartile was 1.69 (p for trend, 0.03).
These results suggest that isoflavones may have exerted an anti-estrogenic effect in breast cancer survivors. This finding contrasts with epidemiologic research involving healthy women which found isoflavone intake was associated with a reduce risk of fracture. Nevertheless, this new finding provides a possible explanation for previously published results from the SBCSS showing that higher isoflavone intake among breast cancer patients was associated with a decreased risk of recurrence and mortality. Therefore, although breast cancer survivors on a high-soy-diet may be less likely to succumb to their disease they may need to take additional measures to prevent bone loss.
Baglia ML, Gu K, Zhang X, et al. Soy isoflavone intake and bone mineral density in breast cancer survivors. Cancer Causes Control. (2015).