Relationship between soy food intake and breast cancer in China

Soy food intake may be associated with reduced risk of breast cancer, by far the most frequent cancer among women, but the results are inconsistent. We aimed to investigate the relationship further in Chinese population and to assess the importance of hormone receptor status.

A case-control study was conducted with totals of 183 cases and 192 controls recruited from January 2008 to January 2011 among patients admitted to the General Hospital of PLA and the Second Affiliated Hospital of Guangzhou Medical University, China. Trained interviewers conducted face-to-face interviews using a structured questionnaire to collect information on dietary habits and potential confounding factors.

The highest relative to lowest soy isoflavone intake was associated with a 58% decrease risk of breast cancer (OR=0.42, 95% CI=0.22-0.80). Higher consumption of soy protein also decreased breast cancer risk, and the highest consumption reduced 54% cancer risk compared with the lowest (OR=0.46, 95%CI=0.24-0.88). The inverse association between highest intake of soy isoflavone and soy protein with the risk of breast cancer was statistically in postmenopausal women (OR=0.57, 95%CI=0.29-0.83; OR=0.50, 95%CI=0.38-0.95). In the ER/PR status stratified analysis, a significantly reduced risk was observed for ER+/PR+ breast cancer among highest intake of soy isoflavone and soy protein, with ORs of 0.47 and 0.63, respectively.

Our study suggested that a high intake of soy food is inversely associated with breast cancer risk, the effect depending to some extent on the hormone receptor status.