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).