Researchers studying American women of Asian descent found that soy intake from childhood through to adulthood was linked to a decreased risk of breast cancer, with the strongest and most consistent association being for childhood soy intake.
The study was the work of senior researcher Dr Regina G. Ziegler, of the Epidemiology and Biostatistics Program, Division of Cancer Epidemiology and Genetics at the National Cancer Institute (NCI) in Bethesda, Maryland, and colleagues and is published in the 24 March online issue of Cancer Epidemiology, Biomarkers and Prevention.
A higher proportion of women get breast cancer in America than in Asia, but when women from Asia migrate to live in the US, their breast cancer risk rises with each generation and eventually becomes the same as that of white American women. This suggests that modifiable factors may be responsible, noted the authors in their background information.
For the population-based case-control study, Ziegler and colleagues interviewed nearly 1,600 women with and without breast cancer who were of Chinese, Japanese and Filipino descent about their cultural practices and the kinds of food they ate as adults and in adolescence. All the participants were living in San Francisco, Oakland in Los Angeles or Hawaii and 73 per cent of the ones with breast cancer were premenopausal.
They also interviewed the mothers of 250 participants about their daughters’ childhood diet.
For the analysis, for each age group (childhood, adolescence, adulthood) the researchers arranged the women according to soya consumption into three sub groups, a high consumption group, a medium consumption group and a low consumption group.
They found that high consumption of soy in childhood was associated with a 58 per cent lower risk of breast cancer, while a high level of soy intake in adolescence and adulthood was linked to a 20 to 25 per cent reduction.
The strong link between high soy consumption and low breast cancer risk was the same for all three races and all three parts of the US, and in women with and without a family history of breast cancer.
The authors concluded that:
“Soy intake during childhood, adolescence, and adult life was associated with decreased breast cancer risk, with the strongest, most consistent effect for childhood intake. Soy may be a hormonally related, early-life exposure that influences breast cancer incidence.”
First author, Dr Larissa Korde, a staff clinician at the NCI’s Clinical Genetics Branch, said in a press statement that:
“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.”
Korde said that since they found childhood soy intake to be significantly linked with reduced breast cancer risk, it suggests that the timing of soy intake could be important.
Although the underlying mechanism is unknown, Korde suggested that these findings point to soy having a biological effect on breast cancer prevention.
“Soy isoflavones have estrogenic properties that may cause changes in breast tissue,” she said, adding that, “animal models suggest that ingestion of soy may result in earlier maturation of breast tissue and increased resistance to carcinogens.”
Ziegler cautioned it is too early to recommend changes in childhood diet based on these results.
“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,” she explained, adding that more studies are needed to confirm these “provocative” results.
” Childhood Soy Intake and Breast Cancer Risk in Asian American Women.”
Larissa A. Korde, Anna H. Wu, Thomas Fears, Abraham M.Y. Nomura, Dee W. West, Laurence N. Kolonel, Malcolm C. Pike, Robert N. Hoover, and Regina G. Ziegler.
Cancer Epidemiol. Biomarkers Prev.Published online first on March 24, 2009.
DOI: 1055-9965.EPI-08-0405v1
Sources: Journal abstract, American Association for Cancer Research .
Written by: Catharine Paddock, PhD