Effects of isoflavones on the coagulation and fibrinolytic system of postmenopausal women

Objective We evaluated the effects of soy isoflavone supplementation on hemostasis in healthy postmenopausal women. Methods In this double-blinded, placebo-controlled study, 47 postmenopausal women 47–66 y of age received 40 mg of soy isoflavone (n = 25) or 40 mg of casein placebo (n = 22) once a day for 6 mo. Levels of factors VII and X, fibrinogen, thrombin–antithrombin complex, prothrombin fragments 1 plus 2, antithrombin, protein C, total and free protein S, plasminogen, plasminogen activator inhibitor-1, and D-dimers were measured at baseline and 6 mo. Urinary isoflavone concentrations (genistein and daidzein) were measured as a marker of compliance and absorption using high-performance liquid chromatography. Baseline characteristics were compared by unpaired Student’s t test. Within-group changes and comparison between the isoflavone and casein placebo groups were determined by a mixed effects model. Results The levels of hemostatic variables did not change significantly throughout the study in the isoflavone group; however, the isoflavone group showed a statistically significant reduction in plasma concentration of prothrombin fragments 1 plus 2; both groups showed a statistically significant reduction in antithrombin, protein C, and free protein S levels. A significant increase in D-dimers was observed only in the isoflavone group. Plasminogen activator inhibitor-1 levels increased significantly in the placebo group. However, these changes were not statistically different between groups. Conclusion The results of the present study do not support a biologically significant estrogenic effect of soy isoflavone on coagulation and fibrinolysis in postmenopausal women. However, further research will be necessary to definitively assess the safety and efficacy of isoflavone.