nattokinase

The short version: the rat and lab data look promising, but the one long, well-built human trial found no benefit on artery measurements, blood pressure, or clotting markers.

The strongest human evidence is a double-blind randomized trial of 265 healthy adults over 55 who took 2,000 fibrinolytic units daily for about three years. It found no reduction in carotid artery thickening, no improvement in arterial stiffness, no blood pressure change, and no shift in any clotting or fibrinolysis marker, including fibrinogen and D-dimers [3]. That is a hard result with a real placebo group and good adherence, around 96% in both arms [3]. It is the trial that should have shown something if the supplement worked as advertised.

The positive claims come from earlier animal and lab work. Rats fed the natto protein for 14 weeks broke down clots faster and lowered fibrinogen, roughly matching an injected clot-dissolving drug in that model [1]. Rats bred to be hypertensive showed modest blood pressure drops at higher doses [2], and lab studies show the enzyme can inhibit ACE, the target of blood pressure drugs [4]. A 2022 review confirms the fibrin-dissolving mechanism is real but concedes the clinical evidence and product standardization are incomplete [5].

The gap between rat results and the human trial is the whole story here. The human trial was in healthy low-risk people, so it cannot rule out benefit in higher-risk groups [3], but for the average person asking whether to take it, the best available trial says it does nothing measurable. Short-term human dosing was tolerated in the small data cited [5], but long-term safety beyond that trial is thin, and anyone on blood thinners faces a plausible additive bleeding risk that has not been studied.

My call: no for prevention in healthy people; the human evidence does not support it. Confidence: moderate.

(Retrieval note: no records surfaced on nattokinase combined with anticoagulants or in patients with existing clots, so those questions stay open.)