Genistein, the major plant-like estrogen from soy linked to lower breast cancer risk

April 18, 2008

Soy supplies us with estrogen like compounds known collectively as phytoestrogens, the major phytoestrogen being Genistein. Researchers found that among more than 24,000 middle-aged or older Japanese women, those with the highest level of Genistein in their blood had a 65 % drop in the likelihood of developing breast cancer over a 10 year period; “This finding suggests a risk-reducing rather than a risk-enhancing effect of isoflavones on breast cancer, even at relatively high concentrations within the range achievable from dietary intake alone," write the researchers, led by Dr. Motoki Iwasaki of the National Cancer Center in Tokyo.
The study included 24,226 women ages 40 to 69 who gave blood samples and completed a dietary assessment, then were followed for an average of 10 years. During that time, 144 women were diagnosed with breast cancer.
When Iwasaki's team separated the women based on their blood levels of Genistein at the study's start, they found that the one-quarter with highest levels were 65 percent less likely to develop breast cancer than the quarter of women with the lowest Genistein levels. There was no risk reduction seen among women with moderate levels of the isoflavone, however.
“Most past studies on soy isoflavones and breast cancer have used dietary questionnaires”, Iwasaki noted. "In contrast, our study used a direct measurement of plasma isoflavone levels, which provides not only an index of intake but also of the absorption and metabolism of isoflavone," the researcher said in an interview with Reuters Health. Together with past studies, Iwasaki said, the findings suggest that a high isoflavone intake from food may help lower breast cancer risk. Japanese women, Iwasaki noted, typically consume soy isoflavones on a regular basis starting from a young age, which may influence the compounds' effects on breast cancer development. The study is published in the April 1, 2008 Journal of Clinical Oncology.

Study suggests soy stops prostate cancer spread

A new animal study adds to the body of research suggesting that soy could help prevent the spread of prostate cancer to other parts of the body and “gives a new basis for hope that Genistein could help prevent the spread of prostate cancer in patients” according to senior investigator Raymond Bergan, MD. Bergan and his team fed Genistein to several groups of mice, and then implanted them with an aggressive form of prostate cancer. The amount of Genistein included in the creatures' chow was no higher than that which a human would consume as part of a diet that includes lots of soy.
While the Genistein did not seem to affect the size of prostate tumors in the mice, it did appear to completely stop lung metastasis (the spreading of cancer cells to other locations in the body). Metastasis was decreased by 96 per cent "Studies of antimetastatic efficacy in man are warranted and are under way," he wrote in his conclusion. Previous studies have indicated that men with a high risk of prostate cancer could benefit from a higher intake of soy isoflavones. The results of the study are published in the March 15, 2008 issue of the Journal Cancer Research.