Childhood soy intake may reduce breast cancer risk

NEW YORK (Reuters Health) - Women who regularly ate soy as children may have a lower risk of developing breast cancer, a study of Asian- American women suggests.

Researchers found that among nearly 1,600 Asian Americans with or without breast cancer, higher soy intake throughout life was associated with a lower risk of the disease. But the strongest protective effect was seen with childhood soy intake.

Women who'd eaten soy regularly as children -- roughly once a week or more -- were about 60 percent less likely to develop breast cancer than women with lower soy intakes in childhood.

Regular soy consumption in adulthood, meanwhile, was linked to a 25-percent reduction in breast cancer risk.

The findings, reported in the journal Cancer Epidemiology, Biomarkers and Prevention, echo those from earlier studies suggesting that soy helps protect against breast cancer.

But they further suggest that childhood soy consumption may be especially important.

Still, it's too soon to make diet recommendations based on the findings, according to the researchers.

"This is the first study to evaluate childhood soy intake and subsequent breast cancer risk, and this one result is not enough for a public health recommendation," senior researcher Dr. Regina G. Ziegler, of the U.S. National Cancer Institute, said in statement issued by the journal. "The findings need to be replicated through additional research."

It's not clear why diets high in soy have been linked to a lower breast cancer risk. In this study, Ziegler's team tried to account for the effects of overall lifestyle by asking the women questions on how "Western" or "Eastern" their lives had been growing up and in adulthood.

Even with those factors considered, childhood soy intake was still linked to lower breast cancer risk, while the connection between adulthood intake and breast cancer risk weakened somewhat.

Some researchers suspect that estrogen-like soy compounds called isoflavones may offer some breast cancer protection. It's been suggested that soy isoflavones block the action of estrogen, promote the destruction of abnormal cells and reduce inflammation in the body.

Exposure to soy isoflavones early in life may be especially important in breast cancer risk, Ziegler and her colleagues speculate. Animal research, they note, has shown that soy may promote earlier maturation of breast tissue and greater resistance of the tissue to cancer-promoting substances.

SOURCE: Cancer Epidemiology, Biomarkers and Prevention, April 2009.