Many women, during menopause take soy based supplements containing plant based phytoestrogens to help prevent hot flashes. According to new research, the dietary supplement, Genistein, a soy isoflavin, can have adverse effects on women undergoing treatment for breast cancer by promoting tumor growth. The new study appears in the journal Carcinogenesis.
Aromatase inhibitors are the mainstay of approximately two-thirds of breast cancer treatment, due to their ability to reduce estrogen levels in the body. According to lead researcher of the study, William Helferich, professor of food science and human nutrition “You have women who are taking these supplements to ameliorate post-menopausal symptoms and assuming that they are as safe as consuming a calcium pill or a B vitamin.” But quite the contrary is true – the researchers found that doses available in supplements can completely negate the effect of breast cancer therapy with Aromatase inhibitors.
Dr. Helferich warns, “These compounds have complex biological activities that are not fully understood. Dietary supplements containing soy-based phytoestrogens provide high enough dosages that it could be a significant issue to breast cancer patients and survivors.” He says dietary supplement containing phytoestrogens have a complex effect on the body, and voices concern about the impact of dietary supplements on breast cancer therapy. Dr. Helferich also notes the findings of a study published last year in Food and Chemical Toxicology that found “female libido enhancement” products, taken at low doses seemed to spur the growth of breast cancer tumors. The same effect wasn’t seen at higher doses.
About two-thirds of breast cancer tumors found in women are estrogen sensitive, meaning the hormone promotes rapid tumor growth. When inhibitor drugs are used, the body produces less aromatase, precursor molecules to estradiol, the main estrogen hormone in women.
The researchers conducted their studies in mouse models with estrogen dependent post-menopausal breast cancer by giving them AD to produce high levels of estrogen to measure the maximum size of breast cancer tumors. Next, they add the aromatase inhibiting drug Letrozole, to block the effects of AD. When they added phytoestrogens, they found that Genistein, at the highest dietary doses, caused the tumors to grow faster, negating the effects of Letrozole.
Menopause means the ovaries no longer produce estrogen. The hormone androstenedione (AD) is still manufactured by body tissue, and then converted to testosterone and estrogen with the aid of aromatase.
“To think that a dietary supplement could actually reverse the effects of a very effective drug is contrary to much of the perceived benefits of soy isoflavones, and unsettling,” says Dr. Helferich. “These findings raise serious concerns about the potential interaction of the estrogenic dietary supplements with current breast cancer therapies.”
The take home message for breast cancer survivors, or anyone undergoing treatment for breast cancer, is to make certain you disclose the use of dietary supplements with your physician. Many people surmise that over the counter health supplements are harmless. It’s important to look at the interaction between all medications, including non-prescription drugs, herbal remedies and supplements when making decisions about managing your health. Women with a family history of breast cancer might also consider the study when choosing natural treatment for relief of menopause symptoms, or products to enhance libido.
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