Women who regularly ate soy as children may have a lower risk of developing cancerous breasts, 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 this so-called 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 cancerous breasts than women with lower soy intakes in childhood.
Regular soy consumption in adulthood, meanwhile, was linked to a 25-percent reduction in cancerous breast tissue risk.
The findings, reported in the journal Cancer Epidemiology, Biomarkers and Prevention, echo those from earlier studies suggesting that soy helps protect against cancerous breasts.
But they further suggest that childhood soy consumption may be especially important.
It's not clear why diets high in soy have been linked to a lower cancerous breast tissue 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 cancerous breast tissue 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.
"Soy isoflavones block the acidic action of estrogen that causes the biological transformation or destruction of healthy body cells, including breast cells. Also, soy isoflavones reduce inflammation in the body by buffering metabolic and dietary acids," states Dr. Robert O. Young, a research scientist at the pH Miracle Living Center, in Valley Center, California.
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 acidic cancerous causing substances.
According to Dr. Young, "Acids from diet, from metabolism and especially from endocrine activity, can be deposited in the breast tissue causing inflammation and potentially leading to cancerous breast tissue. Soy isoflavones can play a key role in chemically neutralizing these acids and therefore may help to prevent a cancerous condition of the breast tissue."
Cancer Epidemiology, Biomarkers and Prevention, April 2009.