Nattokinase

Nattokinase

1. Identity: Chemical Names, Structure, and Natural Source

Subtilisin NAT, commonly known as "nattokinase," is a fibrinolytic enzyme produced by the bacterial strain Bacillus subtilis var. natto, which plays a central role in the fermentation of soybeans into the popular Japanese food natto. Despite its name, nattokinase is not a kinase enzyme but an extracellular serine protease of the subtilisin family (99.5% identical with subtilisin E). It is named for the fact that it is an enzyme produced by nattōkin (Japanese: 納豆菌). This enzyme is known as subtilisin NAT (S08.044) in the MEROPS database. Synonyms include nattokinase, subtilisin QK, and subtilisin QK02.

Nattokinase is a single polypeptide chain composed of 275 amino acids with a molecular weight of 27,724, which displays strong fibrinolytic activity. The gene encodes a prepropeptide with a signal peptide and an inhibitor propeptide before the main enzyme chain (residues 107–381, theoretical molecular mass 27,726.74). The mature protein has a molecular weight of approximately 27.7 kDa and a pI of 6.6.

Nattokinase is a serine protease enzyme obtained from natto, a traditional Japanese food produced from fermented soybeans with Bacillus subtilis, where the enzyme plays a key role in protein degradation during fermentation. Bacillus subtilis is a Gram-positive, rod-shaped, endospore-forming bacterium extensively studied for industrial enzyme production. Its safety, genetic tractability, and efficient protein secretion have established it as an important organism in microbial biotechnology. Due to its Generally Recognized as Safe (GRAS) status and its natural presence in fermented foods, B. subtilis serves as a favorable host for producing bioactive compounds, including therapeutic enzymes like nattokinase.

Similar fibrinolytic enzymes are found in other traditional fermented foods, including chungkook-jang in Korea, douchi in China, thua nao in Thailand, and tempeh in Indonesia. Fermentation technology is used to manufacture nattokinase supplements formulated into powders, pills, and capsules, alone or with other ingredients. Nattokinase was historically extracted directly from natto, but the same molecule can now be produced more efficiently by recombinant means and in batch culture.

2. Traditional and Historical Use

Natto is a traditional Japanese food that has been consumed for at least 1,000 years. The consumption of natto varied geographically, with differences related to the historical fermentation process — for example, the traditional method of using straw wrapping, which retained more nattokinase activity. Japanese children have traditionally eaten natto from early childhood, widely recommended as a supplementary food because of its high protein content and easy digestibility. According to survey data, approximately 70% of Japanese families eat natto more than three times a week, forming a natural and continuous pattern of nattokinase intake.

Natto is believed to have multiple health benefits and has become a folk remedy for heart diseases and fatigue in Japanese culture. The food is traditionally prepared by fermenting boiled soybeans wrapped in rice straw, which naturally harbors Bacillus subtilis spores. The resulting product is characterized by its sticky, stringy texture and pungent aroma, and is conventionally served with rice as a breakfast food.

In 1980, Hiroyuki Sumi, a Japanese researcher at Chicago University Medical School, discovered that natto can dissolve artificial fibrin. Sumi and his team extracted an enzyme from natto that not only degraded fibrin but also a plasmin substrate. He named this novel, fibrinolytic enzyme "nattokinase." This discovery formalized centuries of empirical Japanese awareness of natto's cardiovascular folk benefits into a specific, identifiable bioactive compound.

In non-traditional natto dietary areas such as Europe and the United States, nattokinase is mainly obtained in the form of supplements. However, challenges remain: insufficient dose standardization, large differences in the activity (FU) of commercially available supplements, and some products not labeled with a clear titer.

3. Key Constituents and Active Compounds

Nattokinase itself is the principal bioactive component of interest. As described above, it is a serine protease with 275 amino acids and a molecular weight of approximately 27.7 kDa. Importantly, natto as a whole food contains additional bioactive compounds — most notably vitamin K2 (menaquinone) — that are distinct from nattokinase and are removed or retained to varying degrees in commercial supplement manufacturing.

High concentrations of vitamin K2 in natto can reduce the international normalized ratio (INR) when co-administered with warfarin; this may also occur with nattokinase supplements if vitamin K2 is not removed during the production process. This distinction is clinically important: commercially purified nattokinase supplements vary widely in whether they have been processed to remove vitamin K2.

4. Mechanisms of Action

4.1 Direct Fibrinolysis

Nattokinase can break down blood clots by directly hydrolyzing fibrin and plasmin substrate, converts endogenous prourokinase to urokinase (uPA), degrades PAI-1 (plasminogen activator inhibitor-1), and increases tissue plasminogen activator (t-PA), which supports fibrinolytic activity.

Using a clot lysis assay in vitro, the cleavage of cross-linked fibrin by nattokinase was 6 times more efficient than by plasmin as measured by kcat/Km. At an equivalent molar ratio of doses (0.12 μmol/kg), nattokinase is four times more effective than plasmin at dissolving a thrombus in rats in vivo. These facts suggest that nattokinase has strong fibrinolytic activity both in vitro and in vivo.

4.2 PAI-1 Inactivation and tPA Upregulation

Nattokinase not only degrades fibrin directly and effectively but also increases the release of tPA with a subsequent increase in the formation of plasmin. Plasminogen activator inhibitor 1 (PAI-1) is the primary inhibitor of tPA and regulates fibrinolytic activity in the fibrinolytic cascade. In a study investigating the mechanism by which nattokinase exerted its fibrinolytic effect, NK enhanced fibrinolysis through cleavage and inactivation of PAI-1. In this study, NK was shown to cleave active recombinant prokaryotic PAI-1 into low-molecular-weight fragments as well as enhance tissue-type plasminogen activator–induced fibrin clot lysis.

4.3 Prourokinase Activation

Nattokinase acts directly on fibrin, the main component of blood clots, to decompose it; it activates prourokinase, a precursor to urokinase, a thrombolytic enzyme in the body; and it increases the amount of tissue plasminogen activator (t-PA) that produces thrombolytic enzyme plasmin. Additionally, nattokinase has been found to decompose the thrombolytic inhibitor PAI-1, which makes it difficult for blood clots to dissolve, and has an action of shortening the dissolution time of euglobulin, thereby enhancing thrombolytic activity.

4.4 Effects on Coagulation Factors

In a human single-dose study, D-dimer concentrations at 6 and 8 hours, and blood fibrin/fibrinogen degradation products at 4 hours after nattokinase administration, elevated significantly (p < 0.05). Factor VIII activity declined at 4 and 6 hours (p < 0.05), and blood antithrombin concentration was higher at 2 and 4 hours (p < 0.05).

4.5 Lipid-Lowering Mechanisms

Nattokinase exerts lipid-lowering and anti-atherosclerotic effects by activating hormone-sensitive lipase (HSL), inhibiting hydroxymethylglutaryl monoacyl coenzyme A reductase (HMG-CoA reductase), and enhancing lipoprotein lipase (LPL) activity.

4.6 Antiviral Activity (Preclinical)

SARS-CoV-2 has a spike protein (S protein), and cleavage of the S protein is essential for viral entry. In a laboratory study, when cell lysates transfected with S protein were incubated with nattokinase, the S protein was degraded in a dose- and time-dependent manner. Immunofluorescence analysis showed that S protein on the cell surface was degraded when nattokinase was added to the culture medium. These findings suggest that nattokinase exhibits potential for the inhibition of SARS-CoV-2 infection via S protein degradation. This remains preclinical (cell-based) research only, with no published human clinical trials on this application.

5. Scientific Evidence by Area of Use

5.1 Fibrinolysis and Antithrombotic Effects

Even a single dose of oral nattokinase has been shown to enhance fibrinolysis and anticoagulation in humans. Moreover, nattokinase positively affected various blood rheological parameters in a dose-dependent manner, including platelet aggregation, red blood cell aggregation, whole blood viscosity and vascular tension.

A double-blind, placebo-controlled crossover nattokinase intervention study was carried out in 12 healthy young males. Following baseline blood draw, each subject was randomized to receive either a single-dose of 2,000 FU nattokinase or placebo with subsequent crossover. Subjects donated blood samples at 2, 4, 6, and 8 hours following administration for analysis of coagulation/fibrinolysis parameters. This study provided the first evidence of nattokinase's ability to enhance fibrinolysis and antithrombosis contemporaneously after a single-dose of oral administration in humans. All the blood data changed after nattokinase administration were within the normal range.

Evidence strength: There is consistent mechanistic and early human evidence that a single oral dose of nattokinase measurably alters fibrinolytic parameters in healthy subjects. However, clinical data on fibrinolytic and antithrombotic effects of nattokinase were sparse in the meta-analysis published in 2023, which limits quantitative analysis of these results. Large randomized controlled trials with clinical endpoints (e.g., reduction in thrombotic events) have not been conducted.

5.2 Blood Pressure (Hypertension)

In a randomized, double-blind, placebo-controlled trial, 86 participants ranging from 20 to 80 years of age with an initial untreated systolic blood pressure (SBP) of 130 to 159 mmHg received nattokinase (2,000 FU/capsule) or a placebo capsule for 8 weeks. Seventy-three subjects completed the protocol. Compared with the control group, the net changes in SBP and diastolic blood pressure (DBP) were −5.55 mmHg (95% CI, −10.5 to −0.57 mmHg; p < 0.05) and −2.84 mmHg (CI, −5.33 to −0.33 mmHg; p < 0.05), respectively, after the 8-week intervention. The corresponding net change in renin activity was −1.17 ng/mL/h for the nattokinase group compared with the control group (p < 0.05).

A 2023 meta-analysis pooled six randomized controlled trials with 546 total participants. The analysis found statistically significant reductions in both systolic and diastolic blood pressure with nattokinase supplementation, confirming the direction of effect seen in individual trials. Effect sizes were modest but consistent across studies.

The meta-analysis concluded that nattokinase could be considered as a promising adjunctive tool in the treatment of hypertension.

Evidence strength: Moderate. The blood pressure signal is among the most consistently reproduced clinical findings for nattokinase, supported by at least one reasonably sized RCT and confirmed by a 2023 meta-analysis of six RCTs. However, trials are of short duration (typically 8 weeks), use relatively small sample sizes, and have not established whether the blood pressure reductions translate to reductions in cardiovascular events.

5.3 Atherosclerosis and Lipid Modification

In a clinical study involving 1,062 participants, the efficacy of nattokinase in atherosclerosis and hyperlipidemia at a dose of 10,800 FU/day after 12 months of oral administration was examined. Nattokinase at 10,800 FU/day effectively managed the progression of atherosclerosis and hyperlipidemia with significant improvement in the lipid profile. A significant reduction in the thickness of the carotid artery intima-media and in the size of carotid plaque was observed, with improvement rates ranging from 66.5 to 95.4%.

Nattokinase was found to be ineffective in lowering lipids and suppressing atherosclerosis progression at a dose of 3,600 FU/day. The lipid-lowering effect was more prominent in subjects who smoked, drank alcohol, and subjects with higher BMI. Regular exercise further improved the effects of nattokinase. Co-administration of vitamin K2 and aspirin with nattokinase produced a synergistic effect. No noticeable adverse effects associated with the use of nattokinase were recorded.

In contrast, the 2023 meta-analysis of six shorter-term RCTs found a more nuanced picture: relatively low total dosage of nattokinase supplementation did not exert significant positive effects on levels of total cholesterol, LDL-C, and HDL-C. A previous self-controlled clinical trial also reported no obvious effects of nattokinase (4,000 FU/day, 8 weeks) on lipid parameters in both healthy volunteers and patients with cardiovascular risk factors. These findings were unexpected and inconsistent with results of several animal experiments. One possible explanation is that all included trials used purified nattokinase products, whereas most previous animal studies used crude natto extracts that contained anti-cholesterol agents, such as soy isoflavones.

Evidence strength: Mixed and dose-dependent. The large 1,062-participant study at 10,800 FU/day for 12 months showed meaningful reductions in carotid IMT and plaque area, as well as lipid improvements. However, shorter trials at lower doses (up to 4,000–8,000 FU/day) have not reliably replicated lipid-lowering effects. The 1,062-participant study was not described as a randomized, placebo-controlled trial and has methodological limitations. The body of evidence for lipid lowering is currently preliminary to moderate, and is strongly dose-dependent.

5.4 Cardiovascular Risk Factors — Meta-analytic Summary

In a 2023 meta-analysis, nattokinase supplementation as an intervention to manage cardiovascular risk factors was compared with matching placebo. The daily dosage of nattokinase was highly variable among included trials, ranging from 1,200 to 8,000 FU. All included studies evaluated potential risks of CVDs, including blood coagulation and fibrinolysis factors, blood lipids, blood pressure, and blood glucose.

High-dose nattokinase supplementation produced statistically significant reductions in systolic and diastolic blood pressure (MD = −2.32, 95% CI: −2.72 to −1.92, p < 0.00001) compared with placebo, and led to a slight increase in blood glucose (MD = 0.40, 95% CI: 0.20 to 0.60, p < 0.0001). The high-dose nattokinase group also had higher total cholesterol than control interventions, but no significant differences were found in HDL-C or LDL-C levels. No significant correlation was found between nattokinase supplementation and triglycerides. No notable adverse events were reported in any of the included studies due to intake of nattokinase.

5.5 Neuroprotective and Alzheimer's Disease Research

Beyond its cardiovascular applications, recent research has investigated a broader spectrum of biological activities attributable to nattokinase, encompassing potent anti-inflammatory and antioxidant effects, neuroprotective actions relevant to neurodegenerative disorders including Alzheimer's disease, and potential antiviral properties against SARS-CoV-2.

Nattokinase intake has led to positive outcomes in the pathophysiology of Alzheimer's disease (AD) in rat models. Nattokinase is a natural product with proven safety for human consumption following oral administration. In one study, researchers investigated the protective effects of nattokinase in a rat model of AD induced by aluminum chloride and D-galactose, evaluating effects on learning and memory, levels of Aβ in cerebrospinal fluid, aluminum concentration, and β-amyloid levels by histochemical staining.

Evidence strength: Highly preliminary. Neuroprotective effects are based entirely on animal models and in vitro studies. No human clinical trials have been conducted on nattokinase for Alzheimer's disease or other neurodegenerative conditions.

6. Pharmacokinetics and Bioavailability

The question of whether nattokinase, as a large protein enzyme, survives gastrointestinal digestion and is absorbed in a biologically active form has been a central research question. Its effective delivery is demanding because of stability and bioavailability problems owing to its high molecular weight and proteinaceous nature.

A single-dose study evaluated the pharmacokinetics of oral nattokinase (capsules containing approximately 100 mg of nattokinase [2,000 FU]) in 11 healthy volunteers. Peak serum concentrations were reached at 13.3 ± 2.5 hours after dosing. Because nattokinase was detected in the serum with an enzyme-linked immunosorbent assay using a polyclonal antibody that reacts with both nattokinase and metabolites, it is unclear whether the nattokinase detected in this study was biologically active.

A 2013 article reported that after ingestion of nattokinase by human volunteers, it can be detected in blood using ELISA. However, this is not sufficient proof that nattokinase is absorbed in a functional form, as ELISA frequently cross-reacts with digested versions of an antigen.

Ero and colleagues presented the first bioavailability data of nattokinase in humans by ELISA, demonstrating nattokinase serum activity between 2 and 24 hours in healthy subjects following 2,000 FU administration. Data from a subsequent crossover study, which confirmed an increase in fibrinolysis and anticoagulant parameters between 2 and 8 hours after nattokinase intake, is consistent with these pharmacokinetic results.

The indirect but compelling evidence that fibrinolytic parameters change measurably in human blood after oral dosing strongly suggests that some degree of functionally active absorption — or a functionally equivalent systemic cascade — occurs following ingestion, even if the precise mechanism of action at the gut-blood interface remains under investigation.

7. Dosage Forms and Dosages Reported in Studies

Nattokinase activity is standardized in fibrinolytic units (FU), a measure of the enzyme's capacity to lyse fibrin in vitro. The following dosages have been specifically reported in peer-reviewed clinical studies:

• 2,000 FU/capsule once daily for 8 weeks — used in the primary randomized, double-blind, placebo-controlled blood pressure trial (86 participants with pre-hypertension or stage 1 hypertension).
• 2,000 FU single dose — used in a double-blind, placebo-controlled crossover study in 12 healthy young males to measure acute fibrinolytic and anticoagulant parameters.
• 4,000 FU/day for 8 weeks — reported in a self-controlled clinical trial evaluating lipid parameters in healthy volunteers and patients with cardiovascular risk factors, where no obvious effect on lipids was observed.
• 10,800 FU/day for 12 months — used in the large 1,062-participant clinical study examining atherosclerosis and hyperlipidemia.
• 3,600 FU/day for 12 months — also tested in the same study, and found to be ineffective in lowering lipids and suppressing atherosclerosis progression.
• The daily dosage of nattokinase in the trials included in the 2023 meta-analysis was highly variable, ranging from 1,200 to 8,000 FU.
• Consumption of 10 mg/kg/day nattokinase for 4 weeks was well tolerated in healthy human volunteers in a toxicological assessment.

In non-traditional natto dietary areas, challenges include insufficient dose standardization and large differences in the activity (FU) of commercially available supplements, with some products not labeled with a clear titer.

8. Body Systems Associated with Nattokinase

Nattokinase, an alkaline protease of 275 amino acid residues with a molecular weight of approximately 28 kDa, is the most active ingredient of natto. It has potent fibrinolytic/antithrombotic activity; and in both animal and human studies, nattokinase also has antihypertensive, anti-atherosclerotic, lipid-lowering, antiplatelet/anticoagulant, and neuroprotective actions. All of these pharmacologic actions are relevant to the prevention and treatment of cardiovascular disease.

The body systems for which evidence exists — across a range of quality from in vitro to clinical — include:

• Cardiovascular system: Fibrinolysis, thrombus dissolution, antithrombotic activity, blood pressure regulation, vascular health (carotid IMT and plaque).
• Hematological system: Effects on coagulation factors (Factor VIII, fibrinogen, antithrombin), platelet aggregation, red blood cell aggregation, and whole blood viscosity.
• Metabolic system: Lipid modulation (total cholesterol, LDL, HDL, triglycerides) via HMG-CoA reductase inhibition and lipoprotein lipase activation (established primarily in animal and larger observational studies).
• Neurological system: Beta-amyloid degradation and neuroprotective effects in animal models of Alzheimer's disease (preclinical only).
• Immune/antiviral (preclinical): Degradation of SARS-CoV-2 spike protein in vitro.

9. Safety Considerations and Drug Interactions

9.1 General Toxicological Profile

Nattokinase was non-mutagenic and non-clastogenic in vitro, and no adverse effects were observed in 28-day and 90-day subchronic toxicity studies conducted in Sprague-Dawley rats at doses up to 167 mg/kg/day and 1,000 mg/kg/day, respectively. Mice inoculated with the enzyme-producing bacterial strain showed no signs of toxicity. These findings suggest that the oral consumption of nattokinase is of low toxicological concern. The 90-day oral subchronic NOAEL (No Observed Adverse Effect Level) for nattokinase in male and female Sprague-Dawley rats is 1,000 mg/kg/day, the highest dose tested.

Clinical trials have confirmed safety in humans; in healthy people taking nattokinase for long periods, the incidence of adverse reactions is very low, with occasional minor gastrointestinal discomfort such as bloating or belching, which resolves with dose adjustment.

9.2 Interaction with Anticoagulant and Antiplatelet Agents

Nattokinase has pharmacologic effects that could increase the risk of bleeding when administered with anticoagulant and antiplatelet agents. High concentrations of vitamin K2 in natto can reduce the INR when co-administered with warfarin; this may also occur with nattokinase supplements if vitamin K2 is not removed during the production process.

The combination of nattokinase with anticoagulants like warfarin or direct oral anticoagulants creates additive bleeding risk. Nattokinase enhances fibrinolysis and reduces coagulation factors — effects that compound those of anticoagulant medications, resulting in a higher likelihood of bleeding complications than either agent alone.

There is a theoretical risk of bleeding, based on a case report of acute cerebellar hemorrhage in a patient with a history of ischemic stroke. Thrombosis was also reported after substitution of nattokinase for warfarin in a patient with a mechanical aortic valve. A case report describes a patient who independently substituted nattokinase for warfarin after mechanical aortic valve replacement. After nearly a year of this substitution, the patient presented with prosthetic valve thrombosis, demonstrating that nattokinase cannot provide adequate anticoagulation for high-risk indications.

No systematic data exist on nattokinase combined with direct oral anticoagulants like apixaban, rivaroxaban, or dabigatran.

9.3 Anaphylaxis Risk

Rare cases of late-onset anaphylaxis with natto have been attributed to poly-gamma-glutamic acid, a product of the fermentation process that may be present in nattokinase supplements.

9.4 Vitamin K2 Duality

Nattō is rich in vitamin K. In addition, Bacillus subtilis bacteria in nattō continue synthesizing vitamin K in the intestine following consumption, which can reduce the effects of warfarin. Purified nattokinase supplements manufactured to remove vitamin K2 would not carry this particular risk, but the degree of removal varies by product. Users relying on warfarin therapy should verify the vitamin K2 content of any nattokinase preparation they consider.

9.5 Blood Glucose

The 2023 meta-analysis found that nattokinase supplementation led to a slight increase in blood glucose (MD = 0.40, 95% CI: 0.20 to 0.60, p < 0.0001) compared with placebo. The clinical significance of this finding is uncertain, and it was not reproduced across all individual studies, but it represents a signal warranting attention in future research.

9.6 Evidence Gaps and Overall Assessment

The evidence base needs controlled trials that measure bleeding endpoints, interaction pharmacodynamics, and standardized product formulations before more definitive recommendations can be made. The overall safety profile in short-term human studies has been reassuring, with small, short-term trials evaluating nattokinase reporting no adverse reactions. Risks are theoretical or case-report-based for bleeding in isolation, but become more concrete — and potentially serious — in the context of concomitant anticoagulant or antiplatelet therapy.

References

• Toxicological assessment of nattokinase derived from Bacillus subtilis var. natto — PubMed (2016)
• Crystal Structure of Nattokinase from Bacillus subtilis natto — RCSB PDB (4DWW)
• Nattokinase: An Oral Antithrombotic Agent for the Prevention of Cardiovascular Disease — PMC/IJMS (2017)
• Nattokinase: A Promising Alternative in Prevention and Treatment of Cardiovascular Diseases — PMC (2018)
• A single-dose of oral nattokinase potentiates thrombolysis and anti-coagulation profiles — PMC / Scientific Reports (2015)
• Effects of nattokinase on blood pressure: a randomized, controlled trial (Kim et al., 2008) — PubMed
• Nattokinase Supplementation and Cardiovascular Risk Factors: A Systematic Review and Meta-Analysis of Randomized Controlled Trials — PMC (2023)
• Effective management of atherosclerosis progress and hyperlipidemia with nattokinase: A clinical study with 1,062 participants — PMC / Frontiers (2022)
• Degradative Effect of Nattokinase on Spike Protein of SARS-CoV-2 — PMC (2022)
• Effect of Nattokinase in D-galactose- and Aluminum Chloride-induced Alzheimer's Disease Model of Rat — PMC (2024)
• Research Progress of Nattokinase in Reducing Blood Lipid — PMC/Nutrients (2025)
• Nattokinase Uses, Benefits & Dosage — Drugs.com Natural Products Database
• Nattokinase — Memorial Sloan Kettering Cancer Center Integrative Medicine
• Nattokinase — Wikipedia (for structural/nomenclature data cross-reference)
• Effects of Nattokinase on Blood Pressure: A Randomized, Controlled Trial — Hypertension Research (2008)