The most recent findings on soy and isoflavones were presented in Washington DC on the occasion of the 9th International Symposium on the Role of Soy in Health Promotion and Chronic Disease Prevention and Treatment (October 16-19, 2010). A major part of the topics was dedicated to safety and health benefits in menopausal women, and to the issue of soy and breast cancer.
A comprehensive report can be found here.
Most important results from the point of view of hormonal safety and efficacy in menopausal women:
- - The safety of S-equol has formally been demonstrated in standard models of toxicology including studies in primates. An effect on breast cell proliferation was explicitly excluded with doses corresponding to a human dose of 106 mg, which corresponds to 10 times the established clinically efficacious dose. Safety was also confirmed in clinical safety trials in menopausal women (Jenks 2010). As S-equol is one of the most potent and biologically active isoflavones, the hypothesis of isolated isoflavone bearing a potentially higher risk than natural soy food becomes even more questionable.
- - A cohort study following up on 5042 women with breast cancer examined the impact of soy food and isoflavone exposure on survival rate and cancer recurrence, with special emphasis on tamoxifen-treated patients (which was practically the totality of the group of postmenopausal study participants. Not only had a daily exposure to 30-70 mg of isoflavones from soy food no negative impact on the efficacy of tamoxifen, but in fact the five-year survival and recurrence rates were significantly improved in the women exposed to isoflavones (Shu 2010).
- - Similarly, a reduced recurrence rate was observed in a five-year follow-up of 524 breast cancer patients post surgery and in most cases treated with anastrozole. Although in this study a reduced mortality rate was not confirmed, a daily exposure to > 40 mg of isoflavones clearly had no negative impact on this outcome. In contrast, the high daily exposure to isoflavones significantly reduced the recurrence rate in postmenopausal women by 33 %. This risk reduction was observed in women with ER(+)- and ER(-)-type breast cancer (Kang et al. 2010a). The study was officially published on the day of the presentation (Kang et al. 2010b), and again does clearly not support the hypothesis of postmenopausal women being in danger of developing breast cancer when exposed to isoflavones.
- - Improvement of menopausal symptoms was again clinically established with 30 mg of isolated genistein daily (recently published) (Elliott et al. 2010; Evans et al. 2010), and (also recently published), with 10-30 mg of isolated S-Equol (Aso 2010a; Aso 2010b). A newly presented meta-analysis demonstrated a clear advantage of isoflavones over placebo for the reduction of hot flushes (Taku et al. 2010).
In none of the multiple clinical trials (among others aimed on lipid lowering, bone health and menopausal complaints) could adverse hormonal effects such as changes of endometrial thickness be detected, although these parameters are standard measurements in isoflavone trials.
Conclusions
Soy preparations and even isolated isoflavones have consistently been proven safe and beneficial for human health, especially for menopausal women.
References
Aso, T. (2010b). Equol improves menopausal symptoms in Japanese women. J. Nutr. 140 (7): 1386S-1389S.
