Soy and isoflavone intake associated with reduced risk of ovarian cancer in southern Chinese women

Isoflavones, mainly found in soy, have been shown to inhibit ovarian cancer cell proliferation. We hypothesized that soy consumption and isoflavone intake are related to the risk of ovarian cancer. A case-control study was conducted in southern China to ascertain 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 soy foods, including soybean, soy milk, 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 individual and total soy foods (75.3 ± 53.6 g/day) compared to the controls (110.7 ± 88.8 g/day). Logistic regression analyses showed that regular intake of soy foods could reduce the ovarian cancer risk, the adjusted odds ratio being 0.29 (95% confidence interval 0.20 to 0.42) for 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 (P < 0.001). We concluded that consumption of soy foods is associated with a reduced risk of ovarian cancer in southern Chinese women.