August 28, 2002
     Breast Cancer

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Soy during adolescence may reduce breast cancer

LOS ANGELES -- Aug. 28, 2002 -- When you consume soy foods on a regular basis may play an important role in whether you gain protection against breast cancer, a new study suggests.

Women who regularly ate soy products during adolescence and continued consuming it in adulthood appeared to gain a significant reduction in their breast cancer risk, while women who began soy consumption after reaching adulthood gained little or no reduction in risk.

The research team led by Dr. Anna Wu of the Keck School of Medicine at the University of Southern California found that Asian-American women who consumed soy foods on a weekly basis during their teen years and adulthood had about half the risk of developing breast cancer compared to similar women who ate little soy during the same time period. They reported the findings in the Sept. issue of Carcinogenesis.

"There has been a lot of talk and controversy about the Asian diet and connections between soy food intake and breast cancer," Wu said in a prepared statement. "We wanted to look at soy very carefully to better understand if soy by itself is protective or if the level of soy consumption is just a marker for acculturation."

From 1995 to 1998, Wu and colleagues interviewed 501 Asian-American breast cancer patients and compared them to 594 healthy Asian-American women.

They specifically looked at the importance of soy in the diet, including how many times each week during adolescence they ate tofu. They also asked about the frequency and amounts of whole soy foods, such as tofu, soymilk, miso and fresh soybeans, usually eaten during adulthood.

When women were grouped by how often they ate soy during adolescence and adult life, researchers found that women who were high consumers during both time periods had a 47 percent reduction in risk compared to those who ate little soy during those times.

Those who ate little soy during adult life but were regular soy consumers during adolescence showed a 23 percent reduction in risk Women who were low consumers during adolescence and high consumers during adulthood showed little reduction in risk. However, the number of such women was small, and researchers note that larger studies must be conducted to confirm this result.

Researchers are still seeking to understand the relationship between the amount of soy food needed to produce a risk reduction. In this study, however, the greatest risk reduction was seen among women with the highest level of consumption: 12.68 mg or more of isoflavones per 1000 kilocalories during adulthood and eating soy foods four or more times a week during adolescence.

Wu notes that a much larger study is needed to sort out the benefits of adult soy food intake and what levels of soy intake are most helpful. Her study looked only at traditional soy foods, not at genistein or other isoflavones that may be contained in pills and supplements.