Nattokinase Benefits: What Human Studies Show, Dosage and Safety

Natto, the sticky fermented soybean dish that is a breakfast staple in parts of Japan, is an acquired taste. The enzyme it contains is far easier to take. Nattokinase now shows up in many circulation-support formulas, and plenty of people are searching for nattokinase benefits. The trouble is that a lot of what you read online stretches the science well past what it says.

This guide sticks to the human studies: what nattokinase is, what researchers actually measured, where the results were positive and where they came up empty, how dosing works, and who should check with a doctor first.

What Is Nattokinase?

Nattokinase is a serine protease, a protein-digesting enzyme, produced when soybeans are fermented with Bacillus subtilis var. natto. A 2017 review by Weng and colleagues in the International Journal of Molecular Sciences describes it as a member of the subtilisin family, with a mature form made of 275 amino acids.

Its claim to fame is fibrin. Fibrin is the mesh-like protein that holds a blood clot together, and your body constantly balances building it and breaking it down. According to the Weng review, lab research suggests nattokinase can break down fibrin directly and also influence the body's own clot-dissolving system. Most of that mechanism work comes from lab and animal studies, which is why the human data below matter so much.

What does FU mean?

Nattokinase is dosed in fibrinolytic units (FU), a measure of enzyme activity, not weight. Two products with the same milligrams can deliver very different activity, so FU is the number to compare. The Weng review describes a typical capsule as 2,000 FU per 100 mg.

Nattokinase Benefits: What the Human Research Shows

Three human studies give a fair picture of where the evidence stands. They point in different directions, so it is worth looking at each one.

A single dose changes clotting markers (2015)

Kurosawa and colleagues ran a randomized, double-blind, placebo-controlled crossover study in 12 healthy young Japanese men, published in Scientific Reports. Each man took a single 2,000 FU capsule of nattokinase and, on a separate occasion, a placebo, with blood drawn over the following 8 hours.

Compared with baseline, D-dimer (a fibrin breakdown product) rose about 44.5% at 6 hours, fibrin degradation products rose about 21.2% at 4 hours, and factor VIII activity, a clotting factor, fell about 7.4–7.6% at 4–6 hours. These changes were statistically significant versus placebo. The authors noted that all of these changes stayed within normal ranges. This was a public-grant-funded study and the authors reported no competing interests. It is a useful signal that oral nattokinase has measurable activity, but it measured blood markers for one day in 12 people, not long-term outcomes.

Three years of daily use: no significant difference (2021)

The most rigorous trial to date is the Nattokinase Atherothrombotic Prevention Study, led by Hodis and colleagues. In this double-blind randomized trial, 265 healthy older adults (median age 65) at low cardiovascular risk took 2,000 FU of nattokinase or placebo daily for a median of about 3 years. Researchers tracked carotid artery wall thickness and stiffness by ultrasound every 6 months.

The result was null: nattokinase did not significantly change progression of carotid wall thickness or stiffness compared with placebo, and the laboratory measures, including clotting and inflammation markers, also showed no significant effect. At 2,000 FU per day in low-risk adults, a long, well-designed trial did not find the changes researchers were looking for.

A higher dose in a large observational study (2022)

Chen and colleagues, writing in Frontiers in Cardiovascular Medicine, reviewed records from 1,062 adults (average age 67.5) in China who took 10,800 FU of nattokinase daily for 12 months. Compared with their own starting values, average total cholesterol was 15.9% lower, LDL cholesterol 18.1% lower and HDL cholesterol 15.8% higher, and common carotid wall thickness measured by ultrasound was 21.7% lower. A smaller group taking 3,600 FU per day showed no significant changes.

Read this one carefully. The study was retrospective, had no placebo group and compared people only to themselves, and some participants also took aspirin or vitamin K2. Five of the authors were employed by the company that manufactures the nattokinase used. The authors themselves list the retrospective design as a limitation. It is interesting and it is the main reason higher doses get attention, but it is not the same as a randomized trial.

How Much Nattokinase Should You Take?

There is no official recommended intake for nattokinase. The research has mostly used two levels, and they produced different results in different study designs.

If you are choosing a product, look for the FU number on the label rather than milligrams, take it consistently with food as directed, and bring the label to your doctor if you take any medication that affects clotting.

Nattokinase Safety: Who Should Be Careful

Because nattokinase acts on the clotting system, safety deserves real attention.

• Blood thinners and aspirin: The 3-year trial excluded people taking aspirin, antiplatelet drugs or anticoagulants, so it tells us nothing about safety in those groups. The Weng review cites a published case report of bleeding in the brain in a patient with existing cerebral microbleeds who combined nattokinase with aspirin. PureBlood also contains vitamin K2, and vitamin K can interact with warfarin. If you take any of these medications, do not add nattokinase or PureBlood without your doctor's approval.
• Bleeding disorders and surgery: If you have a bleeding disorder or a procedure scheduled, ask your doctor or surgeon before using it.
• Soy allergy: Nattokinase comes from fermented soybeans. PureBlood contains soy.
• Pregnancy and breastfeeding: These groups have not been studied, so check with your healthcare provider first.

In the Weng review, animal toxicity studies found no significant toxicity, though the authors note repeat-dose safety still needs fuller study.

Where PureBlood™ Fits

PureBlood™ contains 10,800 FU of Nattiase® nattokinase (540 mg) per daily serving. The 2022 results above came from a different nattokinase product in an uncontrolled study, so they should not be read as results for PureBlood. CleanForm pairs Nattiase® with two other ingredients aimed at healthy circulation and heart function: 200 mcg of vitamin K2 as K2VITAL® MK-7 and 2,000 mg of citrus bergamot extract. If you want the background on those, see our guides to vitamin K2 MK-7 vs MK-4 and citrus bergamot benefits.

The serving is 4 capsules daily with a meal. The formula is non-GMO, uses vegetarian capsules and has no artificial additives. Set expectations accordingly: PureBlood is designed to support healthy blood flow and vascular function alongside exercise, diet and sleep, not to replace medical care.

Nattokinase FAQ

What does nattokinase do in the body?

Nattokinase is an enzyme that can break down fibrin, the protein that holds clots together. In a small human study, a single dose shifted several clotting and fibrin-breakdown markers within normal ranges over 8 hours.

Is it safe to take nattokinase every day?

In the 3-year trial, healthy older adults took 2,000 FU daily. Anyone taking blood-thinning medication, with a bleeding disorder, facing surgery, with a soy allergy, or who is pregnant or breastfeeding should talk to a doctor first.

Can I take nattokinase with aspirin?

Not without your doctor's approval. The 3-year trial excluded people on aspirin, antiplatelet drugs or anticoagulants, and a published case report describes bleeding in a patient who combined nattokinase with aspirin.

How long does nattokinase take to work?

Blood markers changed within hours of a single dose in the 2015 study, but that is not the same as a long-term benefit. Studies of longer use ran from 12 months to about 3 years, with mixed results.

The Bottom Line

Nattokinase is a real enzyme with measurable effects on clotting and fibrin-breakdown markers in people. The longer-term evidence is mixed: a rigorous 3-year trial at 2,000 FU found no significant difference from placebo, while a large but uncontrolled, industry-affiliated study at 10,800 FU reported encouraging changes. If you want to try it, choose a product that lists FU clearly, take it consistently, and clear it with your doctor if you use any medication that affects clotting.

---

Sources: Kurosawa Y, et al. A single-dose of oral nattokinase potentiates thrombolysis and anti-coagulation profiles. Sci Rep. 2015;5:11601. · Hodis HN, et al. Nattokinase atherothrombotic prevention study: A randomized controlled trial. Clin Hemorheol Microcirc. 2021;78(4):339–353. · Chen H, et al. Effective management of atherosclerosis progress and hyperlipidemia with nattokinase: A clinical study with 1,062 participants. Front Cardiovasc Med. 2022;9:964977. · Weng Y, et al. Nattokinase: An Oral Antithrombotic Agent for the Prevention of Cardiovascular Disease. Int J Mol Sci. 2017;18(3):523.

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Consult your healthcare provider before starting any supplement.