Effects of Nattokinase on Blood Pressure: A Randomized, Controlled Trial

This Korean randomized trial tested whether nattokinase — a fibrinolytic enzyme from fermented soybeans — could lower blood pressure in pre-hypertensive or stage 1 hypertensive adults.

Eighty-six participants received nattokinase or placebo for eight weeks. The nattokinase group showed statistically significant reductions in systolic (−5.6 mmHg) and diastolic (−2.8 mmHg) pressure. Plasma renin activity also fell, pointing toward the renin-angiotensin system as a plausible mechanism — distinct from nattokinase’s better-known fibrinolytic properties.

A 5 mmHg systolic reduction is meaningful at the population level. If this finding held in larger trials, it would suggest that nattokinase’s blood pressure effects complement — and partially explain — the cardiovascular associations seen in fermented soy observational studies.

The limitation is scale: 86 participants over eight weeks cannot establish long-term benefit or safety. The renin-pathway mechanism, while biologically plausible, requires independent verification and has not been replicated in subsequent well-powered trials.

We rate the evidence moderate. One of the few decent-quality human RCTs on nattokinase, the blood pressure finding is the most credible human-relevant signal in this supplement’s evidence base — and it still awaits replication.