Nattokinase: What Human Studies Show on Blood Pressure and Clotting

Quick answer. Nattokinase is an enzyme made by the bacterium that ferments soybeans into natto, and supplements list its strength in fibrinolytic units (FU). Small human trials, most lasting 8 weeks, found modest drops in blood pressure and short-term changes in some clotting and clot-breakdown lab markers. The largest randomized trial, in 265 older adults who took 2,000 FU a day for a median of 3 years, found no effect on artery-wall thickening, blood pressure or any blood test it measured. Because nattokinase changes clotting tests and bleeding cases have been reported, anyone who takes a blood thinner, has a bleeding problem or is planning surgery should talk to a doctor before using it.

What nattokinase is

Nattokinase, also called subtilisin NAT, is a protein-digesting enzyme made by Bacillus subtilis var. natto as it ferments cooked soybeans into natto, a traditional Japanese food. In lab studies it breaks down fibrin, the protein mesh that holds blood clots together.

Supplements contain a fermented soybean extract in capsules or tablets, labeled in FU: a unit for the enzyme's ability to break down fibrin in a lab test. FU measures activity, not weight. One branded extract reviewed by the European Food Safety Authority (EFSA) is standardized to 20,000–28,000 FU per gram, so 100 mg supplies about 2,000–2,800 FU. The tablets in the 10,800 FU study discussed below held 3,600 FU each.

Natto the food is rich in vitamin K2 (menaquinone-7), about 850 mcg per 3 ounces, according to the NIH Office of Dietary Supplements. Some extracts have the vitamin K2 removed, including the one EFSA reviewed (0.1 ppm or less) and the one used in a North American trial. If this matters to you, check the label or ask the maker.

What human studies have tested

What the findings suggest

Blood pressure. Two 8-week trials at 2,000 FU a day in people with mildly high blood pressure reported small drops, and a meta-analysis of three short trials estimated about 3 mmHg systolic and 2 mmHg diastolic. The 3-year trial, and a later 90-day trial in heart patients, found no blood pressure benefit from nattokinase alone; neither was part of that estimate. Evidence strength: limited and inconsistent.

Clotting and clot breakdown. Short studies show nattokinase changes lab markers within hours to weeks, but over 3 years at 2,000 FU these measures did not differ from placebo. No trial of nattokinase alone has tested whether it prevents or dissolves clots in people. A rat study reported partial breakdown of chemically induced clots; animal results do not show effects in humans. Evidence strength: limited for short-term marker changes; none for clinical clot outcomes.

Cholesterol. In the placebo-controlled trials pooled in a 2023 meta-analysis, nattokinase did not lower cholesterol, and total cholesterol was slightly higher than with placebo. Lower cholesterol was reported in two studies without a placebo group, and lower LDL cholesterol than with placebo in one 90-day trial in heart patients, more than half of whom took statins. Evidence strength: insufficient and conflicting.

Atherosclerosis. The 3-year placebo-controlled trial found no slowing of artery-wall thickening in healthy older adults. The positive reports at 6,000 and 10,800 FU came from studies without a placebo group, both from the same research group. Evidence strength: insufficient.

Where the evidence is limited or conflicting

• Small and short. Most randomized trials enrolled 100 people or fewer and lasted 8 weeks or less. Several used the same branded extract.
• Dose is not settled. Study doses range from 1,200 to 10,800 FU a day, and no effective or safe upper dose has been established.
• Absorption. How much swallowed nattokinase reaches the blood is unknown (see the FAQ). We found no human study comparing delayed-release with ordinary capsules, or doses with and without food.
• Combination products. A single trial of a blend containing nattokinase in 204 high-risk long-haul fliers reported fewer ultrasound-detected clots, and other trials paired nattokinase with red yeast rice. One of them also tested nattokinase alone (see the table); the combination results cannot be credited to nattokinase.
• Funding. Five authors of the 10,800 FU study worked for the tablet maker. The 3-year US trial's registry record names the University of Southern California as sponsor, and its operations manual says a supplement company shipped the capsules; we could not read the paper's funding statement. The North American 8-week trial's registry record lists two companies as sponsor and collaborator. We found no registry record or funding statement for the 2008 South Korean trial.

What buyers say, and what the research shows

Our team analyzed 3,266 public Amazon reviews of 32 nattokinase products, collected in September 2026; one of the 32 is a listing from Vinatura's sister brand, Therexa, and its reviews are included in the counts. Counts come from keyword matching and are approximate. Reviews show what buyers believe or report. They cannot show whether a product caused any change.

Belief: home blood pressure readings show whether it works. In this sample, 289 reviews used home cuff readings as proof. Trial differences averaged a few mmHg. The North American trial required high readings on three separate days to enroll, and many people who first read high did not qualify; the American Heart Association also stresses validated devices. A few home readings cannot separate a supplement's effect from normal variation. That trial excluded people on blood pressure medicine, so anyone who takes such medicine and uses nattokinase should share their readings with their doctor.

Belief: easier bleeding from a small cut is a sign that it works. Fifty reviews treated easier bleeding or bruising from cuts as a sign it was working, and 49 described bleeding or bruising (the groups likely overlap). Trials show longer clotting and platelet times, but bleeding is not a measure of benefit, and serious bleeding has been reported (see Safety). Unusual bruising or bleeding is a reason to stop and call a doctor.

Belief: 10,800 FU is the dose used in studies. One hundred reviews said they wanted the high dose they linked to studies, and 166 showed confusion about per-capsule versus per-serving amounts. The 10,800 FU figure comes from one retrospective study without a control group (see the table). Many placebo-controlled trials, including the longest, used 2,000 FU. A few, lasting 8 weeks to 6 months, used 6,000–8,000 FU. We found no placebo-controlled trial of 10,800 FU.

Belief: nattokinase can be taken with, or instead of, a blood thinner. Some reviews described taking nattokinase alongside a prescription blood thinner, or in place of one. No controlled trial shows either is safe (see Safety). In one published case, a patient who replaced warfarin with nattokinase after receiving a mechanical heart valve developed a clot on the valve after nearly a year and needed repeat surgery. Never stop or replace a prescribed blood thinner without your prescriber.

Some reviews also described using nattokinase for blood clots, deep vein thrombosis or stroke, which are medical conditions that need a doctor's diagnosis and care.

Safety

In trials. A 2023 meta-analysis of seven randomized trials reported no notable adverse events. Most of these trials were small and short, and none was designed to detect rare bleeding. The longest, in 265 people for 3 years, excluded people with bleeding tendencies and people taking blood thinners or regular aspirin. In toxicology tests of one branded extract, rats tolerated up to 1,000 mg/kg a day for 90 days, and healthy volunteers tolerated 10 mg/kg a day for 4 weeks.

Official reviews. In 2016, EFSA concluded that one branded extract was safe for healthy adults over 35 at up to 100 mg a day (at most 2,800 FU), excluding pregnancy and breastfeeding; it did not assess benefits. An older, undated Health Canada notice said the agency could not yet license nattokinase products, citing bleeding risk and an unknown safe dose range. Health Canada has since licensed such products. One licence, issued in 2018 and revised in 2024, says not to use the product during pregnancy or breastfeeding, with products that affect blood clotting, or with a bleeding disorder, and to stop 7 days before scheduled surgery; it also notes that blood in the stool has rarely occurred. We found no official upper intake limit.

Case reports. A woman with brain microbleeds who took aspirin had a bleed in the cerebellum after 7 days of nattokinase at 400 mg a day. A 92-year-old woman with atrial fibrillation, on no blood thinners, who took an unknown amount, died of abdominal bleeding from a ruptured liver cyst after a fall; her doctors suspected nattokinase contributed. Case reports cannot prove cause.

Who should be careful. People taking anticoagulants (such as warfarin or newer oral anticoagulants) or antiplatelet medicines (such as aspirin or clopidogrel); people with bleeding disorders or a past brain bleed; older adults at risk of falls; and anyone facing surgery or dental work (see the FAQ). There are no safety data in pregnancy or breastfeeding.

Soy and vitamin K. Nattokinase is made from fermented soybeans; the extract EFSA reviewed is about 30% fermented soybean extract, and Health Canada's licence conditions note the soy origin. A case letter reports anaphylaxis to nattokinase in a person already allergic to natto. Vitamin K "can have a serious and potentially dangerous interaction" with warfarin, according to the NIH Office of Dietary Supplements, so a product's vitamin K2 content matters to warfarin users.

Interactions. Documented problems come from case reports: the brain bleed with aspirin above, and a valve clot in a patient who replaced warfarin with nattokinase (see buyer beliefs). EFSA judged the available data on warfarin users insufficient to draw conclusions. In the 90-day trial in heart patients, some of whom took aspirin, beta-blockers or ACE inhibitors, no side effects were linked to nattokinase, but the trial was not designed to study interactions. An Italian observational report of 153 vascular surgery patients, some given nattokinase with injected anticoagulants, recorded no adverse drug reactions but had no comparison group. We found no human data for newer oral anticoagulants or clopidogrel.

What research does not establish

• That nattokinase prevents or dissolves blood clots, heart attacks or strokes in people.
• That it slows or reverses plaque in the arteries, or lowers cholesterol.
• That 10,800 FU or other high doses work better, or are safe long term.
• That it is safe to combine with anticoagulant or antiplatelet medicines, or to continue before surgery.
• That delayed-release capsules, an empty stomach or a time of day changes how much reaches the blood.

How we reviewed the evidence

On October 24, 2026, we searched PubMed for nattokinase trials, meta-analyses, case reports, and studies on absorption, toxicology, blood pressure, atherosclerosis, vitamin K, warfarin, surgery, deep vein thrombosis and timing with food. We screened about 190 records by title and abstract (with overlap between searches). We included human trials, one meta-analysis, observational reports and case reports, and used animal and lab studies only to explain mechanisms. We read full texts where PubMed Central had them and abstracts otherwise. We also read EFSA's 2016 opinion, Health Canada's older notice and its Licensed Natural Health Products Database, and the NIH Office of Dietary Supplements vitamin K fact sheet. On October 25, 2026, we read the ClinicalTrials.gov records of the 3-year US trial and the North American 8-week trial, and the 3-year trial's operations manual. Buyer beliefs come from our team's analysis of public Amazon reviews. Vinatura did not run any of these studies.

Vinatura Research Perspective

We asked four questions of each nattokinase study: how many FU a day, in whom, measured how (a lab marker, an artery scan or a clinical event), and run by whom. The answers showed a gap between what is sold and what was tested. The dose buyers cite most, 10,800 FU, comes from a retrospective review of clinic records with no comparison group, co-written by employees of the tablet maker and by the same research group as the only other positive high-dose report, and some participants also took vitamin K2 or aspirin. The longest placebo-controlled trial used 2,000 FU for 3 years in 265 older adults and found no effect on artery thickening, blood pressure or clotting tests, yet the pooled blood pressure estimate did not include it; it also excluded people on blood thinners, so its safety data do not cover them. Online claims that nattokinase "dissolves clots" rest on lab, animal and short-term marker studies, while the same blood-thinning activity underlies the documented bleeding cases.

Our assessment: evidence on blood pressure is limited and inconsistent; short-term changes in clotting markers are real but of unknown clinical meaning; evidence on cholesterol and atherosclerosis is insufficient; and safety with blood thinners is not established. An independently funded, placebo-controlled trial of at least 12 months at the higher doses now sold, with artery imaging and recorded bleeding events, would change this assessment, as would a proper absorption study and an interaction study with common blood thinners.

Where this ingredient appears in Vinatura products

Lumbrokinase Nattokinase Serrapeptase contains 100 mg nattokinase (2,000 FU), 15 mg lumbrokinase and 30 mg serrapeptase per serving, in delayed-release capsules. Its current Amazon listing states that it contains soy and milk. The studies above did not test this product, and none tested nattokinase combined with lumbrokinase and serrapeptase.

Frequently asked questions

What does FU mean on a nattokinase label? Fibrinolytic units, a lab measure of enzyme activity rather than weight. Check whether the number is per capsule or per serving. Many placebo-controlled trials used 2,000 FU a day and a few others up to 8,000 FU; these are study amounts, not a recommendation, so follow your product label.

Does swallowed nattokinase reach the blood? Some appears to. A rat study and an 11-person pilot study detected it in blood, peaking about 13 hours after a 2,000 FU capsule in the pilot, and clotting markers changed within hours of one dose in healthy men. How much is absorbed is unknown, and lab studies disagree on how well it survives stomach acid.

Should I stop nattokinase before surgery or dental work? We found no study that answers this. Health Canada's licence conditions for a licensed nattokinase product tell users to stop 7 days before scheduled surgery. Tell your surgeon or dentist you take it and follow their instructions.

References

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Editorial note: This article reviews published research for educational purposes. It does not establish the effects or safety of any specific supplement, including Vinatura products, and is not medical advice. Written by Vinatura Editorial Team. Last reviewed October 2026.