Ovarian cancer has the eighth highest incidence of all cancers in women, and is the second most common gynecological malignancy. The 5-year prevalence rate for ovarian cancer has exceeded half a million cases worldwide. Rates of this cancer are much higher in the United States and Europe than in Asia, suggesting that soyfood intake might be protective against this disease. Therefore, a case-control study was conducted in southern China to evaluate this hypothesis. Five hundred incident patients with histologically confirmed cancer of the ovary and 500 controls (mean age 59 years) were recruited from four public hospitals in Guangzhou. Information on habitual consumption of soyfoods, including soybean, soymilk, fresh tofu, dried tofu, and soybean sprout, was obtained face-to-face from participants through a validated and reliable semi-quantitative food frequency questionnaire. Isoflavone intakes were then estimated using the USDA nutrient database. The ovarian cancer patients reported lower consumption levels of total soyfoods (110.7 vs. 75.3 g/day). Furthermore, logistic regression analyses showed that regular intake of soyfoods was associated with a 71% reduction in risk when comparing women who consumed at least 120 g/day relative to those less than 61 g/day. Similarly, isoflavone intakes were inversely associated with the ovarian cancer risk, with significant dose-response relationships. These results agree with the existing data so a strong epidemiologic case now exists for soy being protective against ovarian cancer. Furthermore, since estrogen therapy markedly increases risk of ovarian cancer that soyfoods are protective illustrates that soy differs from estrogen and may in fact, be exerting an antiestrogenic effect on the ovaries.
Andy H. Lee, Dada Su, Maria Pasalich, Li Tang, Colin W. Binns, Liqian Qiu. Soy and isoflavone intake associated with reduced risk of ovarian cancer in southern Chinese women. Nutr Research 2014