Nattokinase: Benefits, Forms, Dosing, and Side Effects

Table of Contents

• Overview
• Forms and Bioavailability
• Evidence for Benefits
• Recommended Dosing
• Safety and Side Effects
• Drug Interactions
• Dietary Sources
• References

Overview

Nattokinase is a serine protease enzyme produced by the bacterium Bacillus subtilis var. natto during the fermentation of soybeans to create natto, a traditional Japanese food [1][2]. The enzyme was first identified and extracted from natto in 1987 by Japanese researcher Dr. Hiroyuki Sumi, who discovered its potent ability to dissolve fibrin, the structural protein of blood clots [1][3]. Nattokinase consists of a single polypeptide chain of 275 amino acids with a molecular weight of approximately 27.7 kDa, featuring a conserved catalytic triad (Asp-32, His-64, Ser-221) characteristic of the subtilisin family of serine proteases [2][4].

The enzyme's primary claim to fame is its fibrinolytic activity — the ability to break down fibrin in blood clots. Unlike tissue plasminogen activator (tPA), which works indirectly by converting plasminogen to plasmin, nattokinase cleaves cross-linked fibrin directly into soluble degradation products [2][5]. In addition to this direct mechanism, nattokinase stimulates the release of tPA from vascular endothelial cells and inactivates plasminogen activator inhibitor-1 (PAI-1), enhancing the body's own fibrinolytic system through multiple pathways [5][6]. In vitro studies suggest nattokinase's fibrinolytic strength is approximately four times greater than that of plasmin in dissolving artificial thrombi [7].

Beyond its clot-dissolving properties, nattokinase has demonstrated mild antihypertensive effects through possible inhibition of angiotensin-converting enzyme (ACE), antiplatelet activity via thromboxane blockade, and potential anti-atherosclerotic benefits through reduction of arterial plaque [2][8][9]. It has also been investigated for neuroprotective properties, including the degradation of amyloid-beta fibrils associated with Alzheimer's disease [10][11].

Nattokinase's potency is measured in fibrin degradation units (FU), also called fibrinolytic units, which quantify the enzyme's ability to break down fibrin. This is a critical distinction from simple milligram measurements — the enzyme activity level (FU) is required to know the actual potency of any nattokinase supplement, as milligram amounts alone do not convey functional activity [1]. Commercial preparations are standardized to approximately 20,000 FU per gram (or 20 FU per mg) [12].

The enzyme demonstrates notable biochemical stability, remaining active across a pH range of 6 to 12 and at temperatures up to 60 degrees Celsius [2][13]. However, it is sensitive to acidic conditions and pepsin in the stomach, which has led to the development of enteric-coated formulations and softgel delivery systems to protect the enzyme during oral administration [13][14]. Fibrinolytic effects begin within 2 hours after oral ingestion, with activity persisting for up to 8 hours, and the enzyme has a circulating half-life of approximately 8 to 12 hours — notably longer than conventional fibrinolytic agents like streptokinase [2][7][15].

Despite growing consumer interest, the evidence for nattokinase's cardiovascular benefits comes largely from small, short-term, preliminary clinical studies. Larger, longer, and better-controlled trials are needed to confirm its efficacy for any clinical application [1]. As of 2025, no large-scale Phase III randomized controlled trials have been completed to confirm nattokinase's role in thrombosis prevention across diverse populations [2].

Forms and Bioavailability

Supplement Forms

Nattokinase supplements are available in several delivery formats, each with implications for enzyme stability and absorption:

Standard capsules: The most common form. Nattokinase powder is enclosed in vegetarian or gelatin capsules, typically providing 2,000-4,000 FU per capsule (equivalent to approximately 100-200 mg of enzyme). Standard capsules expose the enzyme to stomach acid, which can degrade a portion of the active enzyme before it reaches the intestine [1][14].

Enteric-coated capsules: Designed with a pH-sensitive coating that resists dissolution in the acidic stomach environment (pH 1-3) and releases the enzyme in the alkaline small intestine (pH 6-7.5), where nattokinase is primarily absorbed. Some researchers recommend enteric coating to protect the enzyme from stomach acid and pepsin, which can inactivate it [14][16]. Several clinical studies showing positive results used enteric-coated formulations [1][3]. However, not all commercial products are enteric-coated, and the necessity of enteric coating remains debated.

Softgel capsules: Nattokinase suspended in oil-based carriers. Absorption of nattokinase into the blood from oral softgel dosing has been confirmed, though it is not always clear whether the softgels used in studies were enteric-coated [17][18]. One study using a single dose of nattokinase in softgel form (NSK-SD, 2,000 FU) demonstrated significant increases in fibrin breakdown markers 4 hours after ingestion compared to placebo [19].

Powdered/functional food forms: Some products offer nattokinase in powdered form for mixing into beverages. These are less common and may expose the enzyme to degradation if mixed with acidic liquids [2].

NSK-SD — A Proprietary Form

NSK-SD (Nattokinase Subtilisin NAT, SD for vitamin K-removed) is a branded nattokinase produced by Japan Bio Science Laboratory Co., Ltd. Its key distinguishing feature is the removal of vitamin K during processing. Since many consumers take nattokinase specifically for its anti-clotting properties, the presence of vitamin K (which promotes clotting) could theoretically counteract this benefit. NSK-SD addresses this concern by providing nattokinase that is claimed to be vitamin K-free [1][20]. NSK-SD has been used in several clinical studies and has been granted novel food authorization in the European Union [21]. A safety study of NSK-SD (552 mg/day for 4 weeks) found it well-tolerated with minimal adverse effects [22].

Vitamin K Content in Nattokinase

This is an important consideration. Natto itself is one of the richest food sources of vitamin K2 (MK-7), with a typical 40-gram single-serving package providing approximately 350 mcg of vitamin K2 — far exceeding the adequate intake of 120 mcg for adult men and 90 mcg for adult women [1][23]. Since vitamin K is essential for blood clotting factor production, this creates a theoretical paradox: natto simultaneously provides a clot-dissolving enzyme (nattokinase) and a clot-promoting vitamin (K2).

During commercial processing of nattokinase for supplements, it is possible to remove or reduce much of the vitamin K content [1]. If avoiding vitamin K intake is a priority — particularly for individuals on anticoagulant medications like warfarin — look for supplements that explicitly state they are vitamin K-free [1]. However, it is worth noting that nattokinase and vitamin K2 coexist naturally in natto without apparent clinical conflict, as the body regulates clotting dynamically through multiple pathways [24].

Absorption and Bioavailability

Nattokinase is absorbed primarily in the small intestine. The enzyme is a protein (275 amino acids), which raises the question of whether it can survive gastrointestinal digestion intact. Evidence suggests that at least a portion of orally administered nattokinase reaches the bloodstream in active form:

• A single dose of 2,000 FU nattokinase (NSK-SD softgel) significantly increased measures of fibrin breakdown and anti-thrombotic factors in the blood 4 hours after ingestion in 12 healthy men [19].
• Oral administration of nattokinase capsules (total daily dose of 1,950 mg) significantly increased measures of fibrin breakdown after 8 days in 12 men [3].
• Consumption of 200 grams of natto itself increased fibrinolytic activity for 2 to 8 hours after ingestion [3].
• Absorption of nattokinase into the blood from softgel forms has been confirmed by pharmacokinetic studies [17][18].

Nattokinase shows some stability against trypsin in the intestinal tract but is sensitive to pepsin and the low pH of the gastric environment [13]. This sensitivity to stomach conditions is why enteric coating, softgel delivery, and empty-stomach administration (which reduces stomach acidity and speeds gastric transit) are commonly recommended strategies to improve bioavailability [14][2].

Empty Stomach vs. With Food

For optimal absorption and systemic fibrinolytic activity, nattokinase is generally recommended to be taken on an empty stomach — for example, 30-60 minutes before meals or at least 2 hours after eating [2]. Taking nattokinase with food may reduce its systemic effectiveness because the enzyme may act primarily as a digestive protease in the gut (breaking down food proteins) rather than being absorbed intact into the bloodstream [2].

Standardization and Potency

Nattokinase potency should be evaluated by fibrinolytic units (FU), not milligrams. Some supplement labels only provide milligram amounts, which are insufficient to determine actual enzyme activity [1]. The relationship between milligrams and FU depends on the purity and concentration of the preparation. As a rough guide, standardized commercial preparations typically provide approximately 20 FU per milligram [12], so a 100 mg supplement standardized to this level would deliver approximately 2,000 FU. However, independent testing has revealed significant variability between products — some products deliver less than half their labeled FU activity, while others contain substantially more than claimed [2]. Always look for products that list FU activity on the label.

Evidence for Benefits

Blood Clots and Thrombosis

Laboratory and animal research suggests nattokinase may help break down blood clots that can block blood flow in arteries (potentially causing heart attacks and stroke) [3][25]. However, evidence of this effect in humans is limited to preliminary studies, and none demonstrate reduced risk of clots using nattokinase alone.

Fibrinolytic activity in healthy subjects: A study in 12 healthy men found that a single dose of nattokinase (NSK-SD softgel, 2,000 FU) significantly increased measures of fibrin breakdown and anti-thrombotic factors in the blood 4 hours after ingestion compared to placebo. Specifically, D-dimer levels rose by approximately 38-45% at 6-8 hours post-administration, indicating enhanced fibrin breakdown and reduced clotting potential [5][19].

Clotting factor reduction: A study found that 4,000 FU of nattokinase (from two enteric-coated capsules) taken daily for two months decreased levels of blood-clotting factors — fibrinogen, factor VII, and factor VIII — by approximately 7% to 19% in healthy people as well as those with cardiovascular risk factors or those undergoing dialysis. Blood pressure remained stable except for a slight decline of -3.73 mmHg in systolic blood pressure [26].

Sustained fibrinolytic activity: A study in 12 men found that taking two enteric-coated capsules three times daily (total daily dose of 1,950 mg of nattokinase) significantly increased measures of fibrin breakdown after 8 days. The same study reported that consuming 200 grams of natto itself increased fibrinolytic activity for 2 to 8 hours after ingestion [3].

Deep vein thrombosis prevention: One study examined a combination of nattokinase and Pycnogenol (pine bark extract) in men and women at high risk for deep vein thrombosis (DVT) who were not taking anticoagulant or anti-thrombotic medication. None of those who took 300 mg of this combination two hours before a long flight (7-8 hours) and again six hours after the first dose experienced a thrombotic event, while seven of those who took placebo developed clots [27]. However, four of the seven women who developed thrombosis had been taking oral contraceptive drugs, which independently increase clot risk. Because the combination product was used, it is not possible to draw conclusions about the effect of nattokinase alone on clot risk.

Real-world observational data: An observational study of 153 patients with vascular diseases found that nattokinase supplementation (approximately 2,000 FU/day) was associated with improved clinical symptoms and no new thrombotic events during follow-up [28].

Epidemiological data from Japan: The Takayama cohort study of over 13,000 adults followed for 15 years found that individuals in the highest quartile of natto intake had approximately 33% lower rates of ischemic stroke mortality compared to non-consumers (HR 0.67, 95% CI 0.47-0.95) [29]. While this is observational and cannot establish causation, it provides population-level data consistent with nattokinase's fibrinolytic properties.

Fibrinaloid microclots: A 2024 in vitro study demonstrated that recombinant nattokinase effectively degrades fibrinaloid microclots — anomalous amyloid forms of fibrin that are resistant to normal fibrinolysis. This suggests potential therapeutic utility for conditions involving persistent microclots, such as Long COVID, though no in vivo or clinical validation exists [30].

Limitations: Most trials feature small sample sizes (n < 100) and short intervention periods (4-12 weeks), precluding definitive conclusions on long-term efficacy. As of 2025, no large-scale Phase III randomized controlled trials have been completed to confirm nattokinase's role in thrombosis prevention across diverse populations [2].

Blood Pressure

Preliminary evidence suggested that nattokinase may help lower blood pressure, possibly through ACE inhibition [8]. However, results from clinical research have been mixed. The benefit, if any, appears to be small and may only persist in the short term (up to 8 weeks).

Positive short-term studies:

A study in men and women with untreated high systolic blood pressure (130-159 mmHg) found that one capsule containing 2,000 FU of nattokinase taken daily for 8 weeks reduced systolic blood pressure by 5.55 mmHg and diastolic blood pressure by 2.84 mmHg compared to placebo [31]. This study also found a net decrease in plasma renin activity (PRA) of -1.17 ng/mL/h compared to placebo (p < 0.05).

In the Hsia et al. (2009) study mentioned above, taking 4,000 FU daily led to a slight decline of -3.73 mmHg in systolic blood pressure but not diastolic blood pressure compared to baseline among healthy adults. However, there was no reduction in systolic or diastolic blood pressure among those with cardiovascular disease [26].

A separate randomized trial (Jensen et al., 2016) in hypertensive individuals found that while overall average PRA did not change significantly, in the subgroup with low baseline PRA (approximately 30% of participants), 66% in the nattokinase group showed normalization to normal levels after 8 weeks compared to only 8% in the placebo group (p < 0.1), with more robust increases in males [32].

Meta-analysis: An analysis of results from three clinical studies (including the Kim et al. study) found that taking 2,000 to 6,000 FU of nattokinase daily for 8 weeks slightly reduced systolic blood pressure by about 3 mmHg and diastolic blood pressure by about 2 mmHg compared to control [33]. A separate 2023 systematic review and meta-analysis encompassing 607 participants overall (with the blood pressure analysis based on 223 participants from 3 RCTs) reported that nattokinase supplementation led to a reduction in systolic blood pressure of 3.45 mmHg (95% CI: -4.37 to -2.18, p < 0.00001) and diastolic blood pressure of 2.32 mmHg (95% CI: -2.72 to -1.92, p < 0.00001), particularly at doses exceeding 100 mg daily [33].

Negative long-term studies:

A US study among 234 adults (average age 65) at low risk for cardiovascular disease showed that taking 2,000 FU of nattokinase (by Jarrow Formulas, which provided the supplement but did not fund the study) daily for 3 years did not significantly lower systolic or diastolic blood pressure compared to placebo [34].

A study in China among 178 adults with stable coronary artery disease showed that taking 3,615 FU of nattokinase in two divided doses daily for 3 months did not significantly lower systolic or diastolic blood pressure compared to placebo [35].

Practical interpretation: Blood pressure reductions appear to be gradual, requiring consistent daily intake over weeks (approximately 8 weeks in key RCTs). No evidence supports sudden or acute blood pressure changes from initial doses. Single-dose pharmacokinetic studies confirm no resting blood pressure alteration shortly after ingestion in normotensive subjects [2]. The overall evidence suggests that any antihypertensive effect is modest (approximately 3-5 mmHg systolic) and may not persist beyond 8 weeks of use, with longer studies failing to show significant effects.

High Cholesterol and Lipid Metabolism

Laboratory research suggested that nattokinase may lower cholesterol levels and reduce atherosclerosis risk through antioxidant effects, reduced lipid peroxidation, and improved lipid metabolism [36]. However, results in humans have generally shown that nattokinase does not significantly improve cholesterol levels compared to placebo.

Negative controlled trials:

An 8-week study in Taiwan among 29 adults (average age 53) with high cholesterol (total cholesterol >200 mg/dL) showed that taking 4,000 FU of nattokinase daily did not significantly improve total cholesterol, LDL cholesterol, HDL cholesterol, or triglycerides compared to placebo [37].

A 6-month study in Taiwan among 46 adults (average age 54) with untreated high cholesterol showed that taking 7,000 FU of nattokinase in two divided doses daily did not significantly reduce levels of cholesterol or triglycerides compared to placebo [38].

A 3-year randomized controlled trial (Hodis et al., 2021) among 234 healthy older adults at low cardiovascular disease risk showed that taking 2,000 FU of nattokinase daily did not significantly improve levels of cholesterol or triglycerides [34].

Meta-analysis (unfavorable): An analysis of data from four clinical studies (including the three described above) showed that taking nattokinase actually increased total cholesterol and had no significant effect on triglycerides, LDL cholesterol, or HDL cholesterol compared to control [33]. Notably, supplementation at relatively low total dosages was associated with adverse changes, including increased total cholesterol and LDL cholesterol levels and decreased HDL cholesterol [33].

One positive observational study (with significant caveats): An analysis of records of 1,062 people (average age 68) in China with high cholesterol levels found that taking 10,800 FU of nattokinase daily for one year reduced triglycerides by 15.7%, total cholesterol by 15.9%, and LDL cholesterol by 18.1%, as well as increased HDL cholesterol by 15.8% [39]. However, this study has many potential weaknesses: it was not a controlled clinical trial, several authors were employees of the nattokinase manufacturer (Sungen), and a "lower dose of 3,600 FU per day" was found to be ineffective — but only 6% of the records analyzed were of patients who took this lower dose, and it is not clear how these patients differed from those given the higher dose [1][39].

Synthesis: The balance of evidence from controlled trials and meta-analyses indicates that nattokinase at standard doses (2,000-7,000 FU/day) does not meaningfully improve lipid profiles. The single large positive observational study used a much higher dose (10,800 FU/day) and had significant methodological limitations including manufacturer conflicts of interest. Nattokinase should not be relied upon as a lipid-lowering supplement.

Atherosclerosis and Arterial Plaque

Given nattokinase's effects on fibrin, clotting factors, and vascular function, several studies have examined whether it can slow or reverse atherosclerosis (plaque buildup in arteries).

Carotid intima-media thickness (CIMT) — negative RCT: The Hodis et al. (2021) 3-year randomized controlled trial in 265 healthy older adults at low cardiovascular disease risk found that 2,000 FU of nattokinase daily did not significantly affect the progression of subclinical atherosclerosis based on the rate of change of carotid artery intima-media thickness (CIMT) or carotid artery stiffness compared to placebo [34].

CIMT and plaque — positive observational study: The Chen et al. (2022) retrospective analysis of 1,062 participants with hyperlipidemia and mild carotid atherosclerosis found that 10,800 FU/day for 12 months significantly reduced CIMT by 21.7% (from 1.33 to 1.04 mm, p < 0.001) and carotid plaque size by 36% (from 24.9 to 15.94 mm², p < 0.001). Improvement rates were approximately 77.7% for CIMT and 66.5% for plaque size. Co-administration of vitamin K2 and aspirin appeared to produce a synergistic effect, and lifestyle factors such as exercise were associated with enhanced outcomes [39]. However, this was a retrospective observational study, not an RCT, so causation cannot be established, and the manufacturer conflict of interest limits confidence in these findings.

Plaque comparison with simvastatin: An earlier clinical study (Ren et al., 2017) in patients with carotid atherosclerosis and hyperlipidemia reported that nattokinase over 26 weeks reduced carotid plaque size by 36.6% and CIMT significantly more than simvastatin, with plaque reduction potentially independent of lipid changes [40]. This finding is noteworthy but has not been replicated in larger controlled trials.

Anti-atherosclerotic mechanisms: Nattokinase's potential anti-atherosclerotic effects include reductions in von Willebrand factor levels by up to 15% and inhibition of platelet aggregation via thromboxane blockade, which collectively may hinder plaque formation and thrombus development [9][41]. Recent research from 2023 to 2025 suggests nattokinase may also improve endothelial function and reduce arterial stiffness in hypertensive patients through modulation of gene expression related to vascular repair [2][42].

Interpretation: For low-risk individuals, the best available evidence (a 3-year placebo-controlled RCT) shows no benefit for atherosclerosis progression at 2,000 FU/day. The positive observational data at much higher doses (10,800 FU/day) in higher-risk individuals is intriguing but requires confirmation in randomized controlled trials before clinical recommendations can be made.

Alzheimer's Disease and Cognitive Function

Nattokinase has been investigated for potential neuroprotective effects based on its ability to degrade amyloid fibrils, anti-inflammatory properties, and vascular benefits.

Amyloid degradation (in vitro): A seminal 2009 study demonstrated that nattokinase can degrade amyloid fibrils, including amyloid-beta 40 (linked to Alzheimer's plaques), insulin fibrils, and prion-related fibrils under physiological conditions (neutral pH, body temperature) [10]. Subsequent 2023 research showed that nattokinase slowly degrades amyloid-beta 42 aggregates and promotes peripheral clearance of amyloid-beta peptides, potentially reducing brain amyloid burden via blood clearance [11].

Animal studies:

A 2023 mouse model using amyloid-beta 1-42 injection found that chronic nattokinase administration (50-100 mg/kg intraperitoneally) prevented memory impairment, anxiety-like, and depression-like behaviors. It reduced hippocampal neuroinflammation (lowered IL-6 and TNF-alpha, increased IL-10), restored BDNF signaling, and normalized neurochemical changes, with effects comparable to donepezil in some measures [11].

A 2024 rat study in a D-galactose plus aluminum chloride Alzheimer's disease model found oral nattokinase (equivalent to 2,600-5,200 FU/kg/day for 10 weeks) reduced amyloid-beta plaques, increased free-form amyloid-beta in cerebrospinal fluid (indicating clearance), removed brain aluminum accumulation, restored brain volume, and improved spatial memory in behavioral tests [43].

Other preclinical work suggests nattokinase may ameliorate blood-brain barrier dysfunction, reduce brain inflammation, and improve cognition in neurodegenerative models. Proposed mechanisms include direct proteolysis of amyloid fibrils, anti-inflammatory effects via cytokine modulation, BDNF restoration, and vascular benefits improving cerebral blood flow [2].

Human clinical evidence (negative): A study among 120 adults (average age 58) with asymptomatic narrowing of the carotid artery or arteries within the skull showed that taking 4,000 FU of nattokinase twice daily for 6 months did not significantly improve overall cognitive function, or measures of visual attention, mental flexibility, verbal memory, working memory, language, executive function, spatial awareness, coordination, recall and recognition, olfactory function, or sleep compared to placebo [44]. A separate 2026 single-center RCT (ICC-PACS, n=88 completers) in patients with asymptomatic intracranial/carotid stenosis found 6 months of nattokinase supplementation did not significantly improve global cognition (MoCA scores) compared to placebo, though exploratory analysis indicated potential benefits in visuospatial function [2].

Synthesis: While preclinical data on amyloid degradation and neuroinflammation reduction are promising, human clinical trials have consistently failed to demonstrate cognitive benefits from nattokinase supplementation. There are currently no studies on nattokinase in people with established Alzheimer's disease. The preclinical mechanisms are interesting but have not translated to measurable human cognitive outcomes.

Metabolism and Insulin Sensitivity

A small randomized trial involving women with obesity and/or diabetes found that nattokinase improved insulin sensitivity, fasting glucose, and HOMA-IR metrics after 3 months, but there was no difference in weight loss compared to placebo — metabolic benefits occurred independently of body weight changes [45]. However, this remains an isolated finding from a small study and should not be interpreted as evidence that nattokinase is effective for metabolic improvement. Nattokinase is not supported by the evidence as an effective supplement for weight loss or body composition improvement [2].

Combination with Red Yeast Rice

Nattokinase is mechanistically distinct from red yeast rice (RYR) and the two are sometimes combined for cardiovascular support. Nattokinase acts as a fibrinolytic enzyme while RYR contains monacolin K, which inhibits HMG-CoA reductase in a statin-like manner to lower cholesterol.

A 2009 randomized, double-blind trial found that combined nattokinase and RYR produced significant reductions in triglycerides (15%), total cholesterol (25%), LDL cholesterol (41%), and TC/HDL-C ratio (29.5%), with HDL cholesterol increases (7.5%), while nattokinase alone showed limited early effects [46].

A 2024 randomized, double-blind, placebo-controlled trial in patients with stable coronary artery disease confirmed the combination's superior lipid-lowering, antihypertensive, and antithrombotic effects compared to either alone or placebo, with improvements in markers like thromboxane B2 and antithrombin III, and no notable adverse events [47]. However, the lipid-lowering effects are likely attributable primarily to the RYR component rather than nattokinase, given the consistently negative lipid data for nattokinase alone.

SARS-CoV-2 Spike Protein

In vitro studies have reported that nattokinase cleaves the SARS-CoV-2 spike protein in a dose- and time-dependent manner, suggesting possible antiviral properties [48]. However, no in vivo or clinical validation exists. These findings remain preliminary laboratory observations and should not be interpreted as evidence that nattokinase treats or prevents COVID-19.

Gastrointestinal Health

Limited evidence from traditional use suggests that natto may benefit gastrointestinal health. The mucus produced during natto fermentation (consisting mainly of gamma-polyglutamic acid and fructans) is believed to coat and protect the gastrointestinal mucosa. Bacillus subtilis in natto can colonize the intestine, secrete enzymes and vitamins to promote proliferation of mucosal cells, and regulate gut microbiota balance [49]. However, these potential effects are primarily theoretical, based on the properties of natto's components rather than clinical trials of nattokinase supplementation specifically. The evidence for gastrointestinal effects is substantially weaker than that for nattokinase's vascular benefits.

Recommended Dosing

Clinical Study Doses

Daily doses between 2,000 FU and 4,000 FU (and 100 mg to 650 mg) have been used in most clinical studies [1]. Due to a lack of definitive clinical evidence, it is not clear what dose is optimal for any specific indication.

Indication	Dose Studied	Duration	Outcome
Fibrinolytic activity	2,000 FU single dose	Acute	Increased fibrin breakdown markers at 4 hours [19]
Clotting factor reduction	4,000 FU/day	8 weeks	Reduced fibrinogen, factor VII, factor VIII by 7-19% [26]
Blood pressure (positive)	2,000 FU/day	8 weeks	SBP -5.55 mmHg, DBP -2.84 mmHg vs placebo [31]
Blood pressure (negative)	2,000 FU/day	3 years	No significant BP reduction vs placebo [34]
Blood pressure (negative)	3,615 FU/day	3 months	No significant BP reduction vs placebo [35]
Cholesterol (negative)	4,000 FU/day	8 weeks	No lipid improvement vs placebo [37]
Cholesterol (negative)	7,000 FU/day	6 months	No lipid improvement vs placebo [38]
CIMT/atherosclerosis (negative)	2,000 FU/day	3 years	No effect on atherosclerosis progression [34]
CIMT/plaque (observational)	10,800 FU/day	12 months	Reduced CIMT by 21.7%, plaque by 36% [39]
Cognition (negative)	8,000 FU/day	6 months	No improvement in cognitive function [44]

Dosing Recommendations by Source

The Japan NattoKinase Association recommends a minimum of 2,000 FU per daily dose for certified supplements [2]. Most supplement products provide 2,000-4,000 FU per capsule.

Higher doses of 10,800 FU/day have been used in the Chen et al. observational study with reported benefits for lipids and atherosclerosis, but this dose has not been validated in controlled trials. A large clinical study involving 1,062 participants demonstrated that 10,800 FU/day for 12 months was safe and well-tolerated [39], though the observational design limits the strength of this safety conclusion.

Timing

Evening/bedtime: Recommended by the Japan NattoKinase Association, based on the rationale that fibrinolytic activity naturally decreases during nighttime hours and is lowest in the morning, potentially increasing the risk of blood clots and heart attacks early in the morning [1][50]. Taking nattokinase at bedtime may provide fibrinolytic protection during this vulnerable window.

Morning (upon waking, before breakfast): Aligns with higher early-morning cardiovascular risk due to elevated PAI-1 levels and supports daytime circulation [2].

Split doses (morning and evening): Can help maintain steadier fibrinolytic activity throughout the day given the enzyme's pharmacokinetics — fibrinolytic activity begins within 2 hours, peaks at 2-4 hours, and persists for 8-12 hours [2].

Empty stomach administration is generally recommended for optimal systemic absorption, as discussed in the Forms and Bioavailability section [2].

Practical Dosing Summary

• General cardiovascular support: 2,000-4,000 FU daily, taken on an empty stomach
• Timing: Evening/bedtime or split morning/evening. Consistency matters more than exact timing
• Look for FU on the label — milligram amounts alone are insufficient to determine potency
• Choose vitamin K-free formulations if the primary goal is anti-thrombotic benefit or if taking warfarin (discuss with physician first)

Safety and Side Effects

General Tolerability

Nattokinase appears to be generally well-tolerated in clinical studies, and serious adverse events have not been reported in short-term studies at standard doses [17][51].

Mild adverse effects reported in clinical studies include diarrhea, common cold symptoms, constipation, stomach pain, menstrual cramps, headache, and one case of an abnormal liver function test [17].

Safety study: A study in 11 men and women found that 5 capsules of NSK-SD taken three times per day with meals (total daily dose of 552 mg/day) for four weeks was well-tolerated, with just one episode of constipation reported. In the women, there was a small but significant decrease in systolic but not diastolic blood pressure [22].

Large-scale safety data: The Chen et al. study involving 1,062 participants at 10,800 FU/day for 12 months reported no noticeable adverse effects, including no significant changes in liver or kidney function [39]. While the observational design limits the strength of this safety finding, it provides some reassurance about tolerability at higher doses.

Long-term safety studies of nattokinase supplementation beyond 12 months are lacking.

Risk of Bleeding

This is the most significant safety concern with nattokinase. The enzyme's anti-thrombotic and blood-thinning effects could increase the risk of bruising or bleeding, particularly when combined with other blood-thinning supplements or medications [1]. This risk extends to any individual undergoing surgery or who may suffer traumatic injury, even if not taking blood-thinning medications.

Fatal hemoperitoneum: A 92-year-old woman who was not taking blood thinners or aspirin but was regularly ingesting nattokinase supplements in unclear amounts ("sometimes a handful") experienced moderate hemoperitoneum (bleeding within the space between the abdominal wall and abdominal organs) after a fall. CT scanning revealed moderate hemoperitoneum with multiple bleeding spots in the liver. The woman opted for conservative management but passed away after one week due to severe low blood pressure and bradycardia [52].

Intracerebral hemorrhage: Bleeding in the brain was reported in one woman with high blood pressure who took 400 mg of nattokinase daily for one week, in addition to taking blood-pressure-lowering medication and low-dose aspirin [53]. This case highlights the particular danger of combining nattokinase with aspirin, especially in individuals with conditions predisposing to cerebral microbleeds.

Theoretical risk of clot embolization: Nattokinase could theoretically loosen an existing blood clot from an extremity (such as a limb), allowing the clot to travel to a potentially more dangerous location such as the heart or lungs [54].

Risk-benefit assessment: For a healthy individual, the potential for increased bleeding from accidental trauma may outweigh any potential benefits of taking nattokinase, particularly given the limited evidence of clinical benefit [1]. Higher doses (such as 400 mg/day) significantly amplify bleeding risk, including severe events like intracerebral hemorrhage, and safety at these elevated doses is not well established [2].

Blood Pressure Lowering

Nattokinase can lower blood pressure, which is a concern for individuals who already have low blood pressure or who take antihypertensive medications. Studies have shown systolic blood pressure reductions ranging from -3.73 to -5.55 mmHg [26][31]. Nattokinase should be used with caution in people with low blood pressure or those on blood-pressure-lowering medications [31].

Allergic Reactions

Soy allergy: Nattokinase supplements derived from soy fermentation may contain soy proteins and should not be taken by people with soy allergies. Some nattokinase supplements claim to be soy-free (produced through fermentation processes not involving soy) [1].

Non-soy anaphylaxis: Severe allergic reactions can occur even in individuals without soy allergies. A 51-year-old man experienced several anaphylaxis episodes over three months, including one approximately 10 minutes after consuming natto. Symptoms included rash, low blood pressure, tingling in the mouth, stomach cramps, nausea, vomiting, diarrhea, and fainting. The man was not allergic to soybeans or soy products such as miso, tofu, or soy milk. However, skin prick tests were positive for whole natto and nattokinase, indicating an allergy specific to the natto fermentation product or enzyme rather than to soy itself [55].

Thyroid Considerations

People with impaired thyroid function should be aware of a theoretical concern that soy can increase the required dose of thyroid hormone medication. This concern may also apply to nattokinase supplements made from soy, although this specific interaction has not been demonstrated in studies [56].

Perioperative Risk

Nattokinase should be discontinued at least two weeks prior to any scheduled surgery to minimize perioperative hemorrhage risk [2][51]. The enzyme's fibrinolytic activity, while generally modest at standard doses, could increase bleeding during and after surgical procedures.

Contraindications

Nattokinase should be avoided or used only under medical supervision in the following situations [2][1]:

• Bleeding disorders or coagulation abnormalities
• Concurrent use of anticoagulant medications (warfarin, heparin) or antiplatelet agents (aspirin, clopidogrel)
• Within two weeks before scheduled surgery (discontinue to minimize perioperative hemorrhage)
• Recent surgery or trauma
• Peptic ulcers, acute gastritis, or bleeding-prone gastrointestinal conditions
• Pregnancy and breastfeeding (insufficient safety data)
• Known allergy to natto, nattokinase, or soy (for soy-derived products)

Drug Interactions

Anticoagulants and Antiplatelet Agents

Nattokinase exhibits anticoagulant properties that may potentiate the effects of the following drug classes, increasing bleeding risk [1][2]:

Drug Class	Examples	Interaction Risk
Anticoagulants	Warfarin, heparin, enoxaparin	High — nattokinase's fibrinolytic action can amplify anticoagulant effects, increasing hemorrhage risk [52][53]
Antiplatelet agents	Aspirin, clopidogrel (Plavix)	High — additive anti-thrombotic effects. The intracerebral hemorrhage case involved aspirin co-administration [53]
NSAIDs	Ibuprofen, naproxen	Moderate — NSAIDs inhibit platelet function, potentially compounding nattokinase's effects [2]

Close monitoring of coagulation parameters, including international normalized ratio (INR), is recommended when nattokinase is used concurrently with any anticoagulant or antiplatelet agent [12].

Antihypertensive Medications

Nattokinase may have additive hypotensive effects when combined with blood-pressure-lowering medications such as ACE inhibitors, beta-blockers, calcium channel blockers, or diuretics. This could potentially lead to orthostatic hypotension (dizziness upon standing) or excessive blood pressure reduction [2][51]. Individuals on antihypertensive therapy should monitor blood pressure closely and consult healthcare providers before starting nattokinase [2].

Blood-Thinning Supplements

Other supplements with blood-thinning properties may compound nattokinase's effects. These include:

• Fish oil / omega-3 fatty acids
• Vitamin E (high dose)
• Garlic supplements
• Ginkgo biloba
• Turmeric / curcumin

Combining multiple supplements with anti-thrombotic properties increases the cumulative bleeding risk [1].

Vitamin K Interactions

The relationship between nattokinase and vitamin K is complex. Natto itself is one of the richest dietary sources of vitamin K2 (MK-7), which promotes blood clotting factor production. However, purified nattokinase supplements (especially NSK-SD) have most vitamin K removed. If taking warfarin — which works by antagonizing vitamin K — the vitamin K content of nattokinase supplements that are not K-free could reduce warfarin's efficacy. Conversely, the fibrinolytic effects of nattokinase could increase bleeding risk when combined with warfarin. This dual concern makes it essential for warfarin users to either avoid nattokinase entirely or use only vitamin K-free formulations under close medical supervision [1][24].

No Known Interactions with Antibiotics

Reliable medical sources, including Memorial Sloan Kettering Cancer Center, Drugs.com, and WebMD, report no known significant drug interactions between nattokinase and antibiotics [2].

Dietary Sources

Natto

Natto is the only significant dietary source of nattokinase. It is a traditional Japanese food made by fermenting steamed soybeans with Bacillus subtilis subsp. natto at approximately 40 degrees Celsius for 24 hours [2][57].

Nattokinase content: A 50-gram serving of natto is estimated to provide between 1,400 to 2,000 FU of nattokinase activity, comparable to a single supplement capsule. However, this content may decrease depending on how natto is cooked or prepared — heat can denature the enzyme [1][58].

Nutritional profile of natto: Beyond nattokinase, natto is a nutrient-dense food providing:

Nutrient	Per 50g Serving (approximate)
Nattokinase activity	1,400-2,000 FU
Vitamin K2 (MK-7)	~350 mcg (per 40g package) [23]
Protein	~8-9g
Fiber	~2.5g
Iron	~4mg
Manganese	~0.6mg
Vitamin C	~6.5mg
Zinc	~1.5mg
Copper	~0.3mg

Characteristics: Natto has a sticky, slippery consistency and a pungent, cheese-like or ammonia-like odor that may be an acquired taste for those not raised on it [1][2]. It is consumed widely in Japan, particularly in the eastern regions, typically served over rice for breakfast.

Preparation considerations: Because nattokinase is an enzyme sensitive to heat, consuming natto fresh or at room temperature preserves more enzyme activity than cooking it at high temperatures. Freezing natto for storage is acceptable, as the enzyme retains activity after thawing. Adding natto to very hot rice or soup may reduce enzyme activity [2].

Other Fermented Soybean Products

While natto is the primary source, other fermented soybean foods from various Asian traditions (such as cheonggukjang from Korea and thua nao from Thailand) may contain related fibrinolytic enzymes produced by Bacillus species, though nattokinase specifically is associated with B. subtilis var. natto and natto production [2].

Recombinant and Non-Soy Production

Modern production methods can generate nattokinase through fermentation processes that do not use soybeans as a substrate, using alternative growth media for Bacillus subtilis. These methods can produce soy-free nattokinase supplements for individuals with soy allergies [1][2]. The enzyme produced through these methods is biochemically identical to soy-derived nattokinase.

References

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