Eating soy regularly as a young girl may help protect against the development of breast cancer later on in life, according to a study reported today in Boston at the American Association for Cancer Research’s Frontiers in Cancer Prevention Research Meeting.

Among 597 Asian-American women with breast cancer and 966 without the disease, researchers found those who ate the most soy-based foods (mainly tofu) between 5 and 11 years of age had a 58-percent lower risk of breast cancer than those who ate the least amount of soy during childhood.

“For high soy intake during adolescence and adulthood, there was about a 25 percent lower risk of breast cancer,” study leader Dr. Larissa A. Korde of the National Cancer Institute, Bethesda, Maryland, told the conference.

This suggests that the timing of soy exposure may be “critical,” Korde said.

“Our study is the first to look at childhood soy intake and breast cancer risk, and found a strong and consistent protective effect for high soy intake in childhood,” she explained.

For those in the highest childhood soy group, the investigators estimate that children ate soy on average a little more than twice a week, while those in the lowest soy group ate soy about once a month. “Stated another way, those in the high intake group ate on average about 10 times more soy than those in the lower group,” Korde said.

It’s long been noted that women living in China and Japan have much lower rates of breast cancer than those living in Western nations. And when women migrate to the US from Asian nations, their risk rises over several generations to approach that of US white women.

“This suggests that the lower risk in Asian women is primarily due to lifestyle factors and one popular theory is that soy intake plays a role,” Korde said.

“Our data suggest that soy intake in early life is itself protective and not just a marker of a broader Asian lifestyle pattern that is protective,” she continued.

The effect of soy was “strikingly consistent” in the study, Korde said noting that the protective effect was evident in women of Chinese, Japanese and Filipino ancestry and in women with or without a family history of breast cancer.

“Our study suggests that soy intake during childhood may have a biologic effect on breast carcinogenesis and further research will be necessary to elucidate the mechanism behind this effect,” Korde said.