Over the past few years women have been given a lot of conflicting information about consuming soy and its relationship to cancer prevention and cancer development. Wading through the information can be daunting. On one hand, eating soy isoflavones is thought to be beneficial for lowering the risk for cancer, heart disease and diabetes. But those health benefits are clouded by its ability to produce the female hormone estrogen, so for some women there may be no benefit at all.
Researchers have determined that soy isoflavones, naturally occurring compounds found in plants, are in fact weak estrogens that have a similar effect on the body as the female hormone estrogen. In recent years, more menopausal women have turned to soy products to calm their accompanying symptoms as an alternative approach to hormone replacement therapy (HRT).
As consumption of soy products, such as soy milk, fresh and dried soy beans, tofu, tempeh, miso and soy sprouts increases annually, there has been a growing concern within the medical community about the effects soy consumption could be having on women, particularly those with estrogen and progesterone receptor positive breast cancer and endometrial cancer. Estrogen fuels tumor growth in these kinds of cancers.
Chinese researchers at the Harbin Medical University Cancer Hospital followed 524 women who had surgery for breast cancer for five to six years to determine the impact of soy isoflavones on breast cancer patients receiving adjuvant endocrine therapy, typically Tamoxifen or Anastrozole.
The study found post-menopausal breast cancer patients with hormone sensitive cancer lowered their risk of recurrence by consuming high amounts of soy isoflavones, but the results did not translate to pre-menopausal women and there was no increase in survival rates for either group.
Dr. Qingyan Zhang and his co-authors stated in the study, published online in the Canadian Medical Association Journal, that post-menopausal patients with the estrogen and progesterone receptor who consumed the highest quantity of soy products (more than 42.3 mg/day) had a significantly lower risk of recurrence by 12.9 percent compared to patients who consumed the lowest amounts (less than 15.2 mg/day). Patients being treated with Anastrozole in the high consumption group realized an 18.7 percent decrease in recurrence.
While epidemiologic evidence has suggested consuming relatively high concentrations of soy isoflavones during adolescence may have a protective effect for developing breast cancer during adulthood, the researchers caution women at high risk for breast cancer and breast cancer survivors that eating soy isoflavone supplements as an HRT alternative is still highly controversial.
“Until now, clinical research has been limited and so there is little clinical evidence to suggest that intake of soy isoflavones increase the risk of breast cancer among healthy women or worsens the prognosis for those who have breast cancer,” the authors stated.
However, the study is not without its limitations. The authors acknowledge it’s possible that other bioactive components in soy, such as soy protein, may have beneficial or harmful effects on breast tissue. Additionally, the authors say the study results should not be applied to the general public since most women eat much lower amounts of soy than what was consumed within the study population.
But the authors agree the findings are potentially important for determining recommendations for soy intake among women receiving endocrine therapy for estrogen and progesterone-receptor positive breast cancers. “Large multi-center clinical trials and other observational epidemiologic studies are needed to confirm these findings,” they said.
The National Natural Science Foundation and the Harbin Science and Technology Bureau supported this study. Two of the study authors have received grants from the National Natural Science Foundation (China).
Lynette Summerill is an award-winning writer who lives in Scottsdale, Arizona. In addition to writing about cancer-related issues, she writes a blog, Nonsmoking Nation, which follows global tobacco news and events.
Source: “Effect of soy isoflavones on breast cancer recurrence and death for patients receiving adjuvant endocrine therapy.” Xinmei Kang MD PhD, Qingyuan Zhang MD PhD, Shuhuai Wang MD, Xu Huang MD, Shi Jin MD. CMAJ, Published online October 18, 2010.