Asian American women who ate higher amounts of soy during childhood had a 58% reduced risk of developing breast cancer, according to a National Cancer Institute study published in the April issue of Cancer Epidemiology, Biomarkers and Prevention, a journal of the American Association for Cancer Research(1). The study focused on women of Chinese, Japanese and Filipino descent living in San Francisco-Oakland, Los Angeles and Hawaii. Researchers interviewed 597 women with breast cancer and 966 healthy women. If the women had mothers living in the United States, researchers interviewed those mothers to determine the frequency of soy consumption in childhood of their offspring.

Historically, breast cancer incidence rates have been 4 to 7 times higher among white women in the U.S. compared to in women in China or Japan. However, when Asian women migrate to the U.S., their breast cancer risk rises over several generations to reach that of U.S. white women, suggesting that modifiable factors, such as diet, rather than genetics, are responsible for the international differences. Previous studies have suggested a protective effect of soy consumption in adults, but the results have been inconsistent. This was the first study to examine the role of childhood soy intake and breast cancer risk.

Researchers divided childhood soy intake into thirds and compared the highest and lowest groups. High intake of soy (>1.5 times/week) during childhood (age 5-11 years) was associated with a 58% reduction in breast cancer. A high level of soy intake in adolescent and adult years was associated with a smaller reduction of 20-25%. The childhood relationship held for all three races (Japanese, Chinese, Filipino), all three study sites (San Francisco-Oakland, Los Angeles, Hawaii), and in women with and without a family history of breast cancer. “Since the effects of childhood soy intake could not be explained by measures other than Asian lifestyle during childhood or adult life, early soy intake might itself be protective,” said the study’s lead investigator, Larissa Korde, M.D., M.P.H., a staff clinician at the NCI’s Clinical Genetics Branch.

According to Dr. Korde, her study suggests early soy intake may have a biological role in breast cancer prevention. “Soy isoflavones have estrogenic properties that may cause changes in breast tissue. Animal models suggest that ingestion of soy may result in earlier maturation of breast tissue and increased resistance to carcinogens,” she said. “This study builds upon the evidence that the antiangiogenic molecules present in soy may be useful for preventing cancer,” said Dr. William W. Li, President and Medical Director of the Angiogenesis Foundation, Cambridge, Mass. “It was shown over a decade ago that the urine of Buddhist monks who consumed soy-based diets contained high levels of genistein, a naturally-occurring angiogenesis inhibitor.”

Notably, genistein exhibits a dose-dependent inhibition of vascular endothelial growth factor (VEGF), a potent angiogenesis stimulator, as well platelet-derived growth factor (PDGF), tissue factor, and matrix metalloproteases, which also promote angiogenesis(2).  Several antiangiogenic drugs designed specifically to inhibit VEGF and PDGF are already FDA-approved to treat colon, kidney, liver, brain, breast, and lung cancers. “This new study is the first to provide strong evidence for a preventative role of soy consumption during childhood,” said Dr. Li.