What is Nattokinase?

Nattokinase is an enzyme produced during the fermentation of soybeans by the bacterium Bacillus subtilis natto — the same process that creates the Japanese food natto. It was first identified by researcher Hiroyuki Sumi in 1980, who discovered its remarkable ability to dissolve fibrin, the protein that holds blood clots together. Unlike many supplements that support the body indirectly, nattokinase works directly on clot-forming proteins in the bloodstream.

How does Nattokinase work?

Nattokinase acts as a fibrinolytic enzyme, meaning it breaks down fibrin clots much like the body's own clot-dissolving system does — but more potently. It also lowers levels of fibrinogen (a clot-building protein), inhibits platelet clumping, and may help relax blood vessel walls to lower blood pressure. Think of it as a natural drain cleaner for your circulation.

What forms does Nattokinase come in?

Nattokinase supplements are most commonly sold as capsules or enteric-coated tablets, measured in fibrinolytic units (FU) rather than milligrams — 2,000 FU is the most researched dose. Enteric coating helps protect the enzyme from stomach acid so it reaches the small intestine intact. Whole natto food contains nattokinase but also Vitamin K2, which is important to know if you're on warfarin.

Where it comes from:

Natto has been a staple of Japanese cuisine for over 1,000 years, particularly in the Kanto region, and was historically valued for its cardiovascular and digestive benefits. The enzyme nattokinase was isolated in 1980 by Dr. Hiroyuki Sumi at Chicago University, who famously discovered its clot-dissolving activity by testing natto on a fibrin clot in a petri dish — the results were striking enough to spark decades of cardiovascular research.

What does Nattokinase help with?

• Blood clots and poor circulation: Nattokinase directly breaks down fibrin, the protein scaffold of blood clots, making it one of the few natural compounds with genuine clot-dissolving ability. It also reduces fibrinogen levels in the blood, which lowers the tendency for new clots to form in the first place.
• High blood pressure: Human trials have shown meaningful reductions in both systolic and diastolic blood pressure with regular nattokinase use. It appears to work partly by inhibiting an enzyme (ACE) that constricts blood vessels, similar to how some blood pressure medications work — but through a gentler, natural pathway.
• Cardiovascular disease risk: By improving blood fluidity, reducing clot-forming proteins, and supporting healthy arterial function, nattokinase addresses several of the underlying drivers of heart attack and stroke risk. Some research suggests it may also slow the buildup of arterial plaque over time.
• Deep vein thrombosis (DVT) prevention: Nattokinase has been studied specifically for long-haul travelers at risk of DVT — the dangerous leg clots that can form during prolonged immobility. One controlled trial found it significantly reduced clot formation and leg swelling during long flights compared to placebo.
• High fibrinogen levels: Elevated fibrinogen is a well-recognized cardiovascular risk marker. Nattokinase has been shown in clinical studies to measurably reduce blood fibrinogen levels, effectively lowering one of the key factors that makes blood 'thick' and clot-prone.
• Atherosclerosis (clogged arteries): Early human research suggests nattokinase may help reduce arterial plaque — the fatty buildup inside artery walls that drives most heart attacks and strokes. Its fibrinolytic and anti-platelet actions may help keep plaques from growing or rupturing.
• Post-COVID clotting concerns: COVID-19 is associated with a hypercoagulable state — blood that clots more easily than normal. Nattokinase has attracted research interest as a natural fibrinolytic agent that may help manage this tendency, though clinical trials specific to post-COVID conditions are still emerging.
• Peripheral artery disease: By improving blood fluidity and reducing clot-building proteins, nattokinase may support better circulation to the legs and feet — areas often compromised in peripheral artery disease. This is a plausible benefit given its mechanism, though direct PAD-specific trials are limited.
• Varicose veins and leg swelling: Some evidence suggests nattokinase can reduce the swelling and discomfort associated with venous insufficiency and varicose veins, likely by improving blood flow and reducing fibrin deposits in and around vein walls.

What can Nattokinase help prevent?

• Deep vein thrombosis (DVT) during long-haul air travel
• Recurrent clot formation in people with elevated fibrinogen
• Progression of arterial plaque buildup

Which foods are rich in Nattokinase?

1. Natto (fermented soybeans): The only direct dietary source of nattokinase — natto is the food from which the enzyme was originally isolated and remains the richest natural source by far.

Practical Tips:

Nattokinase is found almost exclusively in natto, a fermented Japanese food made from soybeans and Bacillus subtilis natto bacteria. Other fermented soy foods like miso or tempeh do not contain meaningful nattokinase. If you are not eating natto regularly, supplementation is the only reliable way to get therapeutic amounts. To support the same cardiovascular goals through diet, focus on: oily fish (omega-3s reduce platelet stickiness), garlic (mild fibrinolytic and anti-platelet effects), dark leafy greens (support vascular health), olive oil (reduces arterial inflammation), and berries (support endothelial function). Avoid excessive alcohol and processed foods high in refined carbohydrates, which promote clotting and vascular inflammation.

What are the side effects of Nattokinase?

• Increased bruising or prolonged bleeding from cuts
• Nausea or mild stomach upset (less common with enteric-coated forms)
• Headache (rare, may relate to blood pressure changes in some users)
• Allergic reaction in people with soy allergy (most supplements use purified enzyme with minimal soy protein, but allergy-prone individuals should check)
• Low blood pressure if combined with antihypertensive medications
• Contraindicated in pregnancy (blood-thinning activity poses risk)

Good to know:

Nattokinase is considered safe for most healthy adults at recommended doses. Its most clinically relevant risk is excessive blood thinning — this matters most for people on medications or heading into surgery. Always pause nattokinase at least one week before any surgical or dental procedure.

How much Nattokinase should you take?

• Recommended daily: 2,000 FU (fibrinolytic units) per day, typically delivered in one 100 mg capsule — this is the most studied dose. Some protocols use 2,000–4,000 FU per day for more active cardiovascular concerns, split into two doses.
• Best time of day: Evening is often recommended since clot risk is naturally higher overnight and in the morning. Some practitioners recommend taking it between meals when possible.
• With or without food: Best taken on an empty stomach or between meals — food (especially protein) may compete with the enzyme and reduce absorption. If stomach upset occurs, a small snack is acceptable.
• Time to effect: Fibrinolytic activity measurable within hours of a single dose; sustained cardiovascular benefits (blood pressure, fibrinogen reduction) typically emerge after 8–12 weeks of daily use.
• How long to take it: Nattokinase can be taken long-term for ongoing cardiovascular support. There is no established cycling protocol. Stop at least 7–10 days before surgery or invasive dental procedures. Reassess with a healthcare provider every 6–12 months, especially if taking other medications.