All study participants ingested 2 nattokinase capsules a day (2000 fibrinolysis units per capsule) for 2 months. At the end of this period levels of fibrinogen had decreased by 9% in the healthy group, by 7% in the CVD group, and by 10% in the dialysis group. Corresponding declines in factor VII level in the 3 groups were 14%, 13% and 7% and for factor VIII 17%, 19% and 19% respectively. No adverse events or increases in uric acid level were observed during the trial.
However, 18% of participants noticed a drop in blood pressure and/or increased vitality. Thirteen percent noticed an improvement in bowel function and 11% reported a lessening of shoulder-neck ache. The Taiwanese researchers conclude that supplementation with nattokinase would have a beneficial effect on risk factors associated with CVD through its reduction in fibrinogen, factor VII and factor VIII levels.
Hsia, CH, et al. Nattokinase decreases plasma levels of fibrinogen, factor VII, and factor VIII in human subjects. Nutrition Research, Vol. 29, 2009, pp. 190-96
Editor's comment: This study confirms that nattokinase is effective in preventing the formation of fibrin-rich blood clots such as those associated with venous thromboembolism and atrial fibrillation (blood stagnation in left atrium or left atrial appendage). Although nattokinase also reduces the level of factor VIII I am not aware of any evidence that it would also reduce the formation of platelet-rich clots (plaque). Additional evidence for the effectiveness of nattokinase in preventing DVT can be found in a study by a group of British and Italian researchers involving 204 airline passengers at high risk for venous thrombosis traveling between London and New York.
 Cesarone, MR, et al. Prevention of venous thrombosis in long-haul flights with Flite Tabs. Angiology, Vol. 54, No. 5, Sept-Oct 2003, pp. 531-39