Facts About Phytoestrogens: The Debate Continues!
The debate about the safety of phytoestrogens has been going on for decades. Research and interest in natural phytoestrogens increased dramatically as a result of the Women’s Health Initiative study published in 1998 demonstrating an increased risk of breast cancer in women taking conventional hormone replacement therapy. But the question remains: are phytoestrogens safe? As scientific evidence continues to mount, the answer may not be as definitive as we would like, but we are getting more clarity around this issue.
Of course, not all phytoestrogens are created equal. Every phytoestrogenacts differently in the human body. Although phytoestrogens are capable of binding to estrogen receptors—hence the name— their binding ability can vary. Bioavailability can also fluctuate among different phytoestrogens. In addition, phytoestrogens from food versus concentrated dietary supplements are also not the same.
According to several studies, phytoestrogens from food are considered safe. A 2013 review published in PLoS One concluded that “soy intake consistent with that of a traditional Japanese diet (2-3 servings daily, containing 25-50 mg isoflavones) may be protective…Human trials show that soy does not increase circulating estradiol or affect estrogen-responsive target tissues.”
A 2018 review published in Phytotherapy Research concluded that “Overall, the existing evidence on phytoestrogens is encouraging, as they appear to be safe when consumed as dietary components of foods.”
When it comes to phytoestrogens in the form of dietary supplements, the conclusions are not as clear but one exception is black cohosh (Cimicifuga racemosa). Many studies have been done to evaluate the safety of black cohosh, which has been shown to have both estrogenic and antiestrogenic effects. AA2014 review published in the journal Integrative Cancer Therapies, included 14 randomized controlled trials, 7 uncontrolled trials, and 5 observational studies demonstrating that black cohosh is safe. A total of 17 of the trials “showed no significant impact on circulating hormone levels or proliferation in estrogen responsive tissues.” How black cohosh exerts hormone balancing actions is still being studied.
Fritz H, Seely D, Flower G, et al. PLoS One. 2013;8(11).
Fritz H, Seely D, McGowan J, et al. Integrative Cancer Therapies. 2014;13(1):12-29.
Senthilkumaar HA, Fata JE, Kennelly EJ. Phytotherapy Research. 2018;1-13.