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Soy may reduce breast cancer mortality

Soy foods are a rich source of isoflavones, which have been linked to a reduced risk of breast cancer. However, the estrogen-like effect of isoflavones may interfere with tamoxifen. Previous studies have indicated that the soy isoflavone genistein promoted estrogen-dependent mammary tumour growth in ovorectomized rats and enhanced the proliferation of breast cancer cells in vitro. These studies have caused concern about the consumption among breast cancer patients. But epidemiological studies have indicated that soy consumption is safe and that the consumption of soy foods is inversely related to the risk of breast cancer. A new study published in the Journal of the American Medical Association (JAMA) confirmed that the intake of soy products may actually reduce the risk of death and breast cancer recurrence.
The researchers analyzed data from the Shangai Breast Cancer Survival Study, involving 5042 female breast cancer survivors, aged between 20 to 75 years. During a follow up of about 4 years 444 deaths and 534 recurrences of breast cancer related deaths were recorded. They found that women with the highest intake of soy protein had a 29 percent lower risk of death and 32 per cent lower risk of breast cancer recurrence compared to patients with the lowest intake. This inverse relationship was evident among women with estrogen receptor positive and estrogen receptor negative breast cancer. Also women who took tamoxifen showed a protective effect of soy protein. The researchers theorized that soy isoflavones protect against breast cancer by competing with endogenous estrogens in the binding of estrogen receptor, resulting in a lower availability of sex hormones, reduced estrogen production and increased clearance of steroids.

The researchers concluded that soy food intake is safe and associated with lower mortality and recurrence among breast cancer patients.

Source: Soy food intake and breast cancer survival. JAMA. 2009 Dec 9;302(22):2437-43.

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