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Soy may slash breast cancer mortality: Study

By Stephen Daniells , 09-Dec-2009
Last updated on 09-Dec-2009 at 13:04 GMT2009-12-09T13:04:41Z

Increased intakes of soy and soy products may reduce the risk of death and breast cancer recurrence, says a new study in the Journal of the American Medical Association.

Women with the highest intake of soy protein had a 29 per cent lower risk of death, and a 32 per cent lower risk of breast cancer recurrence compared to patients with the lowest intake of soy protein, according to findings from a study with Chinese breast cancer survivors.

The study adds to an ever-growing body of science supporting the role of soy, and the isoflavones it contains, with improved breast health.

Soy isoflavones are naturally occurring oestrogen-like compounds, and supplements are currently marketed as a way of reducing symptoms of the menopause and offer an alternative to hormone replacement therapy.

Conflicting reports however have clouded the picture about the beneficial effects of soy isoflavones, with some studies indicating that breast cancer cells in mice were stimulated by the isoflavones. Population studies have shown that women with a high-soy diet generally have lower rates of breast cancer.

“Soy foods are rich in isoflavones, a major group of phytoestrogens that have been hypothesized to reduce the risk of breast cancer. However, the oestrogen-like effect of isoflavones and the potential interaction between isoflavones and tamoxifen have led to concern about soy food consumption among breast cancer patients,” wrote the authors, led by Xiao Ou Shu, M.D., Ph.D., of Vanderbilt University Medical Center.

The researchers analysed data from the Shanghai Breast Cancer Survival Study, a large, population-based study of 5,042 female breast cancer survivors aged between 20 and 75 in China.

After about four years of follow-up, 44 total deaths and 534 recurrences were documented. Soy food intake, as measured by either soy protein or soy isoflavone intake, was inversely associated with mortality and recurrence, said the researchers.

The researchers noted significant reductions in both mortality and breast cancer recurrence with increasing soy protein intake, up to a level of 11 grams per day. After this point, no additional benefits were observed.

We did not find that risk estimates associated with soy isoflavone intake were stronger than risk estimates associated with soy protein intake,” they stated.

“The inverse association was evident among women with either oestrogen receptor–positive or –negative breast cancer and was present in both users and nonusers of tamoxifen,” they continued.

“In summary, in this population-based prospective study, we found that soy food intake is safe and was associated with lower mortality and recurrence among breast cancer patients… This study suggests that moderate soy food intake is safe and potentially beneficial for women with breast cancer,” they concluded.

Source: Journal of the American Medical Association
Volume 302, Issue 22, Pages 2437-2443
“Soy Food Intake and Breast Cancer Survival”
Authors: X.O. Shu, Y. Zheng, H. Cai, K. Gu, Z. Chen, W. Zheng, W. Lu

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