A recent study conducted in Japan reveals that soy products such as tofu may significantly reduce a woman’s chance of developing breast cancer. Details of the study were published in the Journal of Clinical Oncology.

Soy products such as tofu and soybeans contain a compound known as isoflavone, which is structurally similar to human estrogen and may act similarly to estrogen in the body.

The majority of breast cancers are hormone-receptor positive. These cancers are stimulated to grow by the circulating female hormones estrogen and/or progesterone.

For many years the effect of soy products on the risk of breast cancer has been unclear, and previous studies have been inconsistent. It is understood, however, that natural estrogen is much more potent than the estrogen-like chemicals found in soy-based foods. Because of the large variations in soy intake within the Asian countries, researchers were able to study the effect of soy in relatively high doses on the risk of developing breast cancer.

A total of 24,226 women, ages 40-69, responded to baseline questionnaires and provided blood samples from 1990–1995 to detect isoflavone levels. Follow-up continued until December 2002. After an average follow-up of 10 years, 144 patients had been diagnosed with breast cancer. These patients were compared with women within the group who did not develop breast cancer. Isoflavone levels were evaluated by blood samples and by food frequency questionnaires.

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  • Results of the study found that the higher levels of isoflavone were associated with a lower risk for breast cancer.
  • Women with the highest consumption of soy products and high levels of isoflavones were 65% less likely to develop breast cancer than women with low levels of isoflavones.
  • Moderate levels of isoflavone did not produce a reduction in the risk of breast cancer.

Although these results are promising, researchers could not predict if women in Western countries would have the same benefit, as the soy eating patterns of people of Asia and Western countries are quite different.

Reference: Iwasaki, M., Inoue, M., Otani, T., et al. Plasma isoflavone level and subsequent risk of breast cancer among Japanese women: a nested case control study from the Japan Public Health Center Based Prospective Study Group. Journal of Clinical Oncology. 2008; 26: 1677-1683.

Related News:Effect of Soy on Breast Cancer Risk Still Uncertain (4/7/2006)

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