Nattokinase: the clotting claim under scrutiny

The origin story

Nattokinase is an enzyme associated with natto, a traditional Japanese fermented soybean food. Supplement labels often highlight fibrinolytic activity: the ability to act on the system that breaks down fibrin. That mechanism is interesting, but an effect on a laboratory marker cannot by itself show fewer heart attacks or strokes.

What the trials actually tested

In a small placebo-controlled study of people with prehypertension or stage-one hypertension, 73 completed eight weeks; the authors reported lower blood pressure in the nattokinase group. A later trial randomised 265 people without clinical cardiovascular disease to nattokinase or placebo and followed them for a median of three years. It found no significant difference in carotid measurements, blood pressure, coagulation or other assessed markers.

The safety question comes first

A published case report describes a brain haemorrhage after nattokinase was used with aspirin in someone with cerebral microbleeds. A case report cannot quantify the general risk, but it is a strong reason to discuss supplements with a clinician if you use aspirin, anticoagulants or other antiplatelet drugs, have a bleeding disorder, or face surgery. Natto the food and a concentrated supplement also need different consideration, particularly when warfarin and vitamin K are involved.

What would change the picture

Trials powered for clinical outcomes, consistent product quality and clear interaction data would tell us far more than enzyme activity or observational findings. Until then, the defensible headline is “biologically interesting, clinically unproven.”