Podcast episode 146 (in German)
Nattokinase & serrapeptase – what users report and what the studies show
November 23, 2026
Nattokinase from fermented soybeans and serrapeptase from a bacterium in the silkworm gut are sold as a cleaning crew for the arteries. In a large survey, more than half of the patients report feeling better; the longest placebo trial found nothing in the blood vessels.
What it is about
Both enzymes cleave fibrin, the protein mesh of a blood clot; for nattokinase this was shown by a Japanese researcher in Chicago in 1980, and serrapeptase was for decades a medicine against swelling. First the users: in a survey by Stanford and Harvard among people with long COVID or chronic fatigue syndrome, nattokinase and the related earthworm enzyme lumbrokinase did clearly better by self-report than vitamin C, which served as the comparison, but serrapeptase alone did not. Then the studies: for blood pressure, nattokinase shows a small, consistent effect; for plaques, a chart review without comparison stands against a three-year placebo trial without effect. For serrapeptase on blood vessels there is no study. What remains: blood pressure yes, vessel wall no, long COVID open, and at the shelf what matters most is whether you take it in addition to or instead of a medication.
Key points
- A user report, not evidence of efficacy: in the survey with 3,925 responses, 475 people rated nattokinase or lumbrokinase; 55 percent of them felt better by their own account, around one in ten much better, 7 percent worse.
- With vitamin C, which nobody expects to treat these diseases, 27 percent felt better; serrapeptase alone, with 104 ratings, was statistically indistinguishable from it.
- A 2023 meta-analysis of 6 randomized trials with 546 participants found an upper blood pressure value 3.5 millimeters lower and a lower value a little over 2 millimeters lower under nattokinase.
- A 2022 analysis from China with 1,062 participants reported up to 36 percent smaller plaques, without a comparison group and only including those who kept going for 12 months; 5 of the 10 authors work for the manufacturer.
- The counter-test by the University of Southern California with 265 people without heart disease, double-blind over about 3 years, found no difference in the vessel wall, in blood pressure or in any lab value.
- A 2026 Australian review, for which doctors and patients set priorities, counts nattokinase among the 14 most important candidates for testing in long COVID; there are no studies in humans.
- Takeda withdrew its serrapeptase product from the market in Japan in 2011 after it was not significantly better than placebo in double-blind trials; in Europe, serrapeptase is not approved as a food.
Where the data stop
Whether swallowed nattokinase reaches the blood as an active enzyme was left open by the European Food Safety Authority in 2016; individual coagulation values shift for a few hours after a capsule. The novel food authorization in the EU rests on rat experiments and an assessment for healthy adults over 35. Nobody has tested the patients from the survey, often taking other remedies and some on blood thinners. The survey itself remains self-reporting by people who are active in groups; it cannot separate whether the gap to vitamin C comes from the enzyme or from greater hope.
The risks hinge on the word “instead”: from Taiwan, a cerebellar hemorrhage has been described after one week of nattokinase in addition to aspirin, and from Texas a clot on an artificial heart valve after a man replaced his anticoagulant on his own. For serrapeptase there are isolated reports of lung inflammation as a hypersensitivity reaction. Anyone taking anticoagulants or aspirin or facing surgery discusses taking it with a doctor beforehand.
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Published on November 23, 2026.
The topic in the database
- An enzyme from fermented soybeans (natto): supports the flow properties of the blood and cardiovascular health.Nattokinase
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Information only, not medical advice and not a usage or dosage recommendation. Prescription-only and unapproved substances belong in the hands of a physician. Last updated: 2026-09-25.