BOSTONConsuming soy during childhood, adolescence, and adult life is associated with a decreased risk of breast cancer, but the strongest and most consistent effect is childhood consumption, according to a recent collaborative study led by researchers from the National Cancer Institute (NCI), and presented at the AACR Frontiers in Cancer Prevention Research meeting (abstract B163).
The scientists reported that women who ate the most soy-based foods such as tofu, miso, and natto (a traditional Japanese food made from soybeans) during ages 5 to 11 reduced their risk of breast cancer by 58%, compared with the women who ate the least amount. The reductions for adolescence and adulthood were about 25%. "In our study, soy intake during childhood is strongly protective against breast cancer later in life," said Larissa Korde, MD, MPH, of the NCI's Division of Cancer Epidemiology and Genetics.
The study was a case-control analysis of Asian-American women living in Los Angeles, San Francisco, and Oahu, Hawaii. Dr. Korde collaborated with epidemiologists at the University of Hawaii, Northern California Cancer Center, and University of Southern California.
The researchers interviewed approximately 1,500 women of Chinese, Japanese, and Filipino descent, ages 20 to 55, about their diet and lifestyle over the course of their lives597 were breast cancer cases and 966 were controls. For study participants whose mothers were alive and living in the United States, the researchers also interviewed 255 mothers about their daughters' early exposures.
Soy intake was divided into thirds, based on frequency of consumption. Women in the highest category consumed, on average, 2 servings per week while those in the lowest category ate soy an average of once a month, resulting in a 10-fold difference in exposure to soy between the two extremes. By comparing the highest category to the lowest, the researchers found inverse associations between the risk of developing breast cancer and the amount of soy consumed. The strongest effect was for childhood consumption.
It is well known that women living in China and Japan have lower breast cancer rates than those living in western nations. Many studies have also shown that the breast cancer rates of women who migrate from Asian countries to the United States rise over several generations and approach that of US white women. This change in rates suggests that environmental or lifestyle factors play a role in the changing rates. One leading candidate is soy.
One of the advantages of working with migrant populations is that as they acculturate, they begin to acquire the habits of the host country over time and as a group have a wide range of exposures to environmental factors. This range of exposures would be difficult to observe outside a migrant community.