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Eating soy foods during childhood may reduce breast cancer risk

Previous epidemiologic studies have already linked the consumption of soy foods with a reduced risk of breast cancer. Wu and co-workers at the University of Southern California were the first to conduct an epidemiologic case-control study specifically designed to investigate this association. They found that women consuming soy foods on a regular basis during adolescence and adulthood had half the risk of developing breast cancers than those who only eat little soy foods. They came to this conclusion after conducting a case control study in Asian women living in the US.
The researchers compared soy intake (expressed as mg isoflavones) of 501 Asian women with breast cancer and 594 controls living in the Los Angeles County. Intake of soy foods was highest with Chinese women (27 mg isoflavones per day), intermediate with Japanese women (18 mg isoflavones per day) and lowest with Filipino women (9 mg isoflavones per day). The main source of isoflavones is tofu, followed by soy milk, miso and fresh soybeans. Women consuming much soy foods during adolescence and adulthood showed a 47% lower risk of developing breast cancer, whereas this risk was 33% for those consuming much soy foods only during adolescence. The researchers tried to find mechanisms explaining the protective activity of soy food intake. Animal studies showed that early life exposure to the isoflavone genistein reduced the number of chemically induced mammary tumours and favourably influenced the morphology of mammary glands. Soy foods may also work by binding to estrogen receptors.

The study concluded that high soy food intake by Asians living in the US during adolescence was associated with a significant reduced risk of breast cancer and that this risk may be further reduced by high intake as an adult.

Source: Adolescent and adult soy intake and risk of breast cancer in Asian-Americans. Carcinogenesis. 2002 Sep;23(9):1491-6.

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