Soy safe for breast cancer: Study
Yen Yen Yip
Soy intake may not harm breast cancer survivors, and could even help reduce their risk of death and cancer recurrence, according to recent results from a population-based study of more than 5,000 breast cancer survivors.
The study marks the latest update in the controversy between soy – which has often been touted as a “miracle food” – and breast cancer. [JAMA 2009;302(22):2437-2443]
The association between soy and breast cancer recurrence originally surfaced in a 2001 literature review, which reported that the isoflavones contained in soy foods – genistein and daidzein – were found to stimulate breast tumor growth in animal studies. The authors noted that women with current or past breast cancer should be alerted to this potential risk. [Ann Pharmacother 2001;35(9):1118-1121] In 2006, while conceding that soy may reduce the risk of breast cancer through various possible mechanisms, another review recommended that “the impact of isoflavones should be evaluated at the cellular level in women at high risk for breast cancer.” [J Natl Cancer Inst 2006;98(18):1275-1284]
Apart from the role of isoflavones in cancer cell growth, other in vivo and in vitro data had also suggested a potential interaction between soy isoflavones and tamoxifen. [Nutr Rev 2009;67(7):398-415]
Against a backdrop of such concerns, the Shanghai Breast Cancer Survival Study was conducted to evaluate the association of soy food intake among breast cancer patients with cancer recurrence. In the study, 5,042 female breast cancer survivors in China, aged 20 to 75, were followed up for a median period of 3.9 years. This is the largest population-based study of breast cancer survival to date.
The results showed that soy protein intake was inversely associated with mortality and recurrence. Patients with the highest levels of soy protein intake had a 29 percent lower risk of death and a 32 percent reduced risk of recurrence, compared to those with the lowest consumption levels. This dose response relationship follows a linear pattern until soy protein intake reaches 11 g per day or soy isoflavone intake reaches 40 mg per day.
“After these points, the association appears to level off or even rebound,” the investigators reported. The benefits applied regardless of whether the women had estrogen-receptor positive or negative breast cancer, or early- or late-stage cancers.
The authors of the study also uncovered an interesting link between tamoxifen use and soy food intake. Soy consumption was associated with improved survival regardless of tamoxifen use. However, in contrast, tamoxifen only improved survival among subjects with low or moderate soy intake. For women who had the highest level of soy intake, tamoxifen did not improve survival rates.
“More importantly, women who had the highest level of soy food intake and who did not take tamoxifen had a lower risk of mortality and a lower recurrence rate than women who had the lowest level of soy food intake and used tamoxifen, suggesting that high soy food intake and tamoxifen use may have a comparable effect on breast cancer outcomes,” the authors wrote.
Sumber: MIMS Online