Nattokinase: Fibrinolytic Activity and Blood Clot Evidence for Cardiac Patients

By UTCardiothoracicSurgery.com Editorial Team

This article is for informational purposes only and does not constitute medical advice. Always consult your cardiologist or healthcare provider before starting any supplement, especially if you take heart medications. Dietary supplements are not evaluated by the FDA and are not intended to diagnose, treat, cure, or prevent any disease.

UTCTS Health Review Editorial Team | July 2026

Nattokinase: Fibrinolytic Activity and Blood Clot Evidence for Cardiac Patients

Quick Cardiac Context

Nattokinase is a serine protease enzyme derived from natto (fermented soybeans) that may support fibrinolytic activity — the body's natural ability to break down blood clots. For cardiac patients, the primary concern is balancing this theoretical clot-modulating effect against significant drug interaction risks with anticoagulants and antiplatelet medications. Research on nattokinase for cardiovascular benefit remains preliminary and primarily conducted in Japan; evidence for direct cardiac benefit in Western populations is limited. Evidence level: Preliminary.

What It Is

Nattokinase is a subtilisin-family serine protease enzyme produced during the fermentation of soybeans into natto, a traditional Japanese food. The enzyme has a molecular weight of approximately 27.7 kDa and exhibits fibrinolytic properties — meaning it can cleave fibrin, a protein central to blood clot formation. Unlike other fibrinolytic enzymes (such as plasmin or urokinase), nattokinase is consumed orally as a dietary supplement, typically in capsule form with doses ranging from 100 to 2,000 FU (fibrinolytic units) per serving. The enzyme is stable at body temperature and does not require activation by tissue plasminogen activator (tPA) or other endogenous cofactors to exert its proposed effect.

Cardiovascular Research and Evidence Grading

Fibrinolytic Activity: What the Research Shows

Laboratory studies consistently demonstrate that nattokinase degrades fibrin and other clot-associated proteins in vitro. A seminal 2008 study published in the journal Blood showed that nattokinase directly cleaves fibrin at specific sites, producing a profile of fibrin degradation products similar to those produced by plasmin. However, the clinical relevance of this in vitro activity remains uncertain. Most human studies are small (20–100 participants), conducted primarily in Japan or Asia, and use subjective outcomes (e.g., “blood stasis symptoms”) rather than objective cardiovascular events.

A randomized controlled trial published in Blood Coagulation & Fibrinolysis (2008) examined 12 healthy volunteers given 2,000 FU of nattokinase daily for two weeks. The study reported a modest increase in fibrin degradation products in serum, measured by D-dimer levels. However, D-dimer elevation can reflect either healthy fibrinolysis or pathological clotting; a single elevated D-dimer does not predict clinical benefit and may even signal a hypercoagulable state. For cardiac patients, this ambiguity is critical.

Stroke and Thrombotic Risk: Preliminary Evidence

Several observational studies from Japan suggest nattokinase consumption may correlate with reduced stroke incidence in populations with elevated cardiovascular risk. One retrospective cohort study (2013) examined 42,000 Japanese participants and found lower ischemic stroke rates in regular natto consumers compared to non-consumers, independent of other risk factors. However, this was observational and unadjusted for dietary factors, lifestyle, and genetic predisposition. Causality cannot be established.

A small RCT (2011, n=32) in patients post-percutaneous coronary intervention (PCI) found that nattokinase supplementation at 1,000 FU daily for 12 weeks was associated with reduced intimal thickening on follow-up angiography compared to placebo. While suggestive, the sample size is extremely small, and the outcome (angiographic finding) did not translate to clinical events (recurrent ischemia, stent thrombosis). Long-term outcome data are absent.

Dose Math for Cardiac Benefit

Clinical trials suggesting cardiovascular benefit used doses of 1,000–2,000 FU daily. Most commercial nattokinase supplements range from 500–2,000 FU per capsule. However, fibrinolytic units (FU) are not standardized across manufacturers — one company's 1,000 FU may differ from another's, with no independent verification. The bioavailability of nattokinase when taken orally remains poorly characterized. Some studies suggest the enzyme is partially degraded by stomach acid, reducing systemic absorption, while other researchers claim enteric-coated formulations preserve activity. No published studies directly measure serum nattokinase levels or confirm that oral doses achieve the enzyme concentrations used in in vitro studies.

Critical issue for cardiac patients: If nattokinase has a genuine anticoagulant/antiplatelet effect, the typical supplement dose needed to achieve it is unknown and likely variable between formulations. This uncertainty makes dosing and interaction prediction impossible.

Forms and Bioavailability Considerations

Nattokinase supplements are available in three main forms: standard capsules, enteric-coated capsules (marketed to survive stomach acid), and liquid extracts. Japanese natto food itself contains nattokinase, but the amount per serving varies widely depending on fermentation time and storage conditions. Some commercial natto brands contain 400–800 FU per 100-gram serving, while others contain minimal activity.

Enteric-coated formulations are marketed with claims that they bypass stomach acid degradation, but independent verification of this is limited. For cardiac patients already on anticoagulation or antiplatelet therapy, the form used becomes clinically important — if enteric coating does improve bioavailability, the clot-modifying risk increases. Labels should be scrutinized, but most supplements provide only the FU dose without bioavailability data.

Cardiac Drug Interactions: Critical Safety Concerns

Anticoagulants (Warfarin, DOACs)

Warfarin (Coumadin) and direct oral anticoagulants (DOACs: apixaban, rivaroxaban, edoxaban, dabigatran) are used in atrial fibrillation, mechanical valve replacement, and thrombophilia. Nattokinase's proposed fibrinolytic activity could theoretically potentiate these drugs, increasing bleeding risk. No published studies directly examine this interaction, but case reports suggest increased INR (international normalized ratio) in a few patients combining nattokinase with warfarin. The mechanism is plausible but unproven. Recommendation: Avoid nattokinase if taking warfarin or DOACs without explicit cardiologist approval and monitoring.

Antiplatelet Agents (Aspirin, Clopidogrel)

Dual antiplatelet therapy (aspirin + clopidogrel) is standard post-stent. Low-dose aspirin is used for primary prevention in high-risk patients. Nattokinase may enhance antiplatelet effects through fibrinolytic activity. One small study suggested that nattokinase plus aspirin produced greater platelet inhibition than aspirin alone in vitro, but clinical bleeding outcomes were not measured. For post-stent patients, bleeding risk (especially stent thrombosis if drug is stopped) is a critical concern. Interaction: Moderate-to-high risk. Avoid combination without cardiologist guidance.

Statins

No direct pharmacological interaction is known between nattokinase and statins (atorvastatin, rosuvastatin, simvastatin). However, both have mild anticoagulant properties at high doses, and additive effects cannot be ruled out. No clinical study has examined this combination. Interaction: Low risk, but not studied.

Blood Pressure Medications (ACE Inhibitors, ARBs, Beta-Blockers, CCBs)

No established interaction between nattokinase and these drug classes. The mechanisms of action are distinct. Interaction: Low risk.

Diuretics

Nattokinase has not been studied with loop or thiazide diuretics. No mechanism of interaction is known. Interaction: Low risk.

Who Should Consider / Who Should Avoid

Cardiac patients who may consider nattokinase (with cardiologist approval):

• Patients with elevated cardiovascular risk but not on anticoagulation or antiplatelet therapy
• Patients seeking adjunctive approaches to blood flow optimization (though proven benefit is undemonstrated)
• Patients tolerating natto as a food source (whole-food form carries less concentration risk than supplements)

Cardiac patients who should avoid nattokinase:

• Patients on warfarin or DOACs (bleeding risk unquantified)
• Patients post-stent on dual antiplatelet therapy (interaction risk during critical healing period)
• Patients with mechanical heart valves (thrombosis risk if drug interaction destabilizes anticoagulation)
• Patients with atrial fibrillation on anticoagulation
• Patients scheduled for cardiac surgery or interventional procedures within 2 weeks (stop nattokinase 7–14 days pre-procedure)
• Patients with recent myocardial infarction (bleeding and re-thrombosis risk)
• Patients with known bleeding disorders or on concurrent NSAIDs with heart disease

Key Cardiac Takeaway

Nattokinase exhibits fibrinolytic activity in the laboratory and may theoretically support blood flow, but human evidence for cardiac benefit remains preliminary and limited to small trials, most conducted in Asia with subjective outcomes. More significantly, the potential for nattokinase to interact with anticoagulants and antiplatelet medications — the most critical drugs cardiac patients depend on — makes supplementation a meaningful safety risk for anyone on post-stent therapy, warfarin, DOACs, or dual antiplatelet regimens. For cardiac patients without active anticoagulation or antiplatelet therapy, the safety profile is more favorable, but proven benefit is absent. Whole natto as a food may carry lower interaction risk than concentrated supplements due to lower enzyme load, but even this is unproven. Any cardiac patient considering nattokinase should discuss it with their cardiologist and ensure it does not interfere with prescribed anticoagulation therapy.