Small studies suggest that nattokinase can mildly lower blood pressure in some people; however, it's not clear if this effect persists in the long term. A clinical study in 86 patients with high blood pressure showed that taking 100 mg (2,000 fibrinolytic units (FU)) of nattokinase daily for 8 weeks reduced systolic blood pressure by about 6 mmHg and diastolic blood pressure by about 3 mmHg compared to a placebo.[1] Another small study in adults without known health conditions showed that taking 552 mg (11,040 FU) of nattokinase (NSK-SD) daily for four weeks resulted in small and variable decreases in blood pressure. However, the reduction in diastolic blood pressure was only statistically significant in female participants.[2]
The blood-pressure-lowering effect has been attributed to peptides in denatured nattokinase which inhibit the angiotensin-I-converting enzyme (ACE). Denaturing the nattokinase enzyme with heat and simulated stomach contents seems to yield more of these peptides, as shown in animal and in vitro research.[3][4] A laboratory study using simulated digestion, or exposing nattokinase to the stomach digestive enzymes pepsin and trypsin, showed that the enzyme fragments had greater ACE-inhibitory activity than nattokinase itself.[5]