Nattokinase comes up regularly in questions to our nutrition team, usually from someone who has heard about it from a family member, seen it mentioned alongside heart health, or been handed a bottle by a friend who swears by it. The question is almost always the same: is this worth taking, and what does it actually do? It is a reasonable thing to want a straight answer to, and a surprisingly difficult one to find.
Nattokinase is an enzyme produced during the fermentation of soybeans into natto, a traditional Japanese food. It is not a vitamin, not a mineral, and not a plant extract, which makes it slightly unusual among supplement ingredients and explains why the research on it looks different too.
In the UK, health claims about foods and food supplements can only use wording that has been reviewed and approved by regulators, held on a public list called the GB Nutrition and Health Claims Register. Nattokinase does not currently hold any authorised claims on that register. That does not mean the enzyme has not been studied. It just means the research is not yet at the point where regulators have approved specific claims about what it does, and any article covering it should describe what has been investigated rather than what a reader should expect.
What Is Nattokinase?
Natto is a food before it is anything else. Soybeans are steamed and then fermented with a bacterium called Bacillus subtilis, producing a dish with a sticky, stringy texture and a strong flavour that tends to divide opinion outside Japan, where it has been eaten for centuries.
Nattokinase is produced by the bacterium during that fermentation. It is not present in unfermented soy, which means soy foods generally and natto specifically are not interchangeable in this context. The enzyme exists because of the fermentation, not because of the bean.
It was first described in 1987 by the Japanese researcher Dr Hiroyuki Sumi, who was investigating naturally occurring substances capable of breaking down fibrin.
Nattokinase belongs to a family of enzymes called serine proteases. These break down proteins, and the protein most closely associated with nattokinase research is fibrin. Fibrin is produced by the body as part of normal clotting and tissue repair. When a blood vessel is damaged, fibrin forms a mesh that holds a clot together while the tissue underneath recovers. It is a normal and necessary process, and the body produces and breaks down fibrin continuously.
Most published research on nattokinase centres on its interaction with fibrin. That single property is the reason the enzyme has been investigated across the areas covered below, and understanding it makes the rest of the picture easier to follow.
How the Enzyme Works
The body has its own enzyme for breaking down fibrin, called plasmin. Fibrin is laid down where it is needed and cleared away when it is not, and that balance is part of normal circulatory function.
In laboratory conditions, nattokinase has been shown to break down fibrin directly. Researchers have also examined whether the enzyme influences the body’s own fibrinolytic pathways rather than acting on fibrin alone, and this remains an open question rather than a settled one.
Here the evidence needs stating clearly because it is frequently glossed over. A large proportion of nattokinase research is in vitro, meaning it was carried out on samples in a laboratory rather than in people, or was conducted in animal models. Human trials exist, but they are smaller and fewer than the volume of discussion around the ingredient would suggest. Laboratory findings describe what an enzyme does to a sample under controlled conditions. They do not establish what happens when a supplement is swallowed.
That distinction matters more than usual with nattokinase, because it is a protein. How well an orally taken enzyme survives digestion, and in what form it reaches the bloodstream, is also a subject of ongoing research.
What Research Has Investigated
Published research on nattokinase has looked at several areas. In each case, the findings describe what happened under study conditions and should not be read as effects a reader can expect.
- Circulation and blood flow, including how fibrin breakdown behaves in laboratory conditions
- Blood pressure measurements in small human trials
- Blood lipid measurements, including cholesterol and triglycerides
- Arterial changes over time in a small number of longer-term studies
- Mucus viscosity and fibrin content in tissue and fluid samples taken from people with chronic sinus conditions
- Laboratory work on amyloid-beta, a protein studied in the context of neurodegeneration
The sinus and respiratory research deserves a closer look, partly because it is less familiar than the circulatory work and partly because it is often described inaccurately.
The study most often referred to was published in Allergology International in 2017 by a research group at the University of Fukui in Japan. Samples of nasal polyp tissue were incubated with nattokinase solutions at a range of concentrations for 24 hours, and samples of nasal discharge and sputum were incubated with the enzyme for one hour. The tissue samples showed fibrin degradation, and the mucus samples became less viscous under those conditions.
This was laboratory work carried out on samples that had been taken from people during surgery. It was not a trial in which people took a supplement and were then assessed. Those are different kinds of evidence, and the difference is routinely lost when this study is summarised online.
That gap is worth flagging because anyone who has read about nattokinase and nasal polyps has probably encountered the shorter version: that nattokinase shrinks nasal polyps. However, what the study actually showed is that the enzyme broke down fibrin in polyp tissue in a dish. Between that finding and a person swallowing a capsule sits digestion, absorption, dose, and whether the enzyme reaches the tissue at all.
The researchers proposed the enzyme as a candidate for further development, and framed their findings as raising a possibility worth pursuing rather than as an established use. That is a statement about a direction for research, not about what a food supplement does when taken by mouth. Any further work would need to establish what happens after digestion, at what dose, and with what safety profile before anything could be said about outcomes in people.
The same caution applies to the laboratory work on amyloid-beta. It is early-stage research on protein behaviour, and it is a long way from anything that could be said about cognition in people.
Safety and Who Should Take Care
Nattokinase is one of the ingredients where a conversation with a doctor is important because the enzyme has fibrinolytic activity. This means it interacts with something the body is already managing carefully, and that makes it worth checking before starting supplementation. Anyone in the following groups should speak to a doctor or pharmacist first:
- Anyone taking anticoagulant or antiplatelet medication, including warfarin, aspirin, clopidogrel, or a direct oral anticoagulant (DOAC)
- Anyone with a bleeding disorder
- Anyone due to have surgery or a dental procedure, who should discuss stopping in advance
- Anyone who is pregnant or breastfeeding
- Anyone with low blood pressure or taking blood pressure medication
- Anyone with a soy allergy, as nattokinase is derived from fermented soybeans
Side effects reported in studies have generally been mild and gastrointestinal. Anyone who notices unusual bruising, nosebleeds, or bleeding that takes longer than usual to stop should stop taking it and seek advice. Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle.
Nattokinase in Supplement Form
Nattokinase supplements are measured in fibrinolytic units (FU) rather than by weight. This is because enzyme preparations vary in how active they are, so a figure in milligrams says little on its own about what a product contains. The FU figure describes activity, which is the more meaningful measure, and it is worth checking on any label.
The quality of a nattokinase supplement depends on more than the amount listed on the label. Factors such as the source of the enzyme, manufacturing standards and the type of capsule used can all influence product quality. Because nattokinase is an enzyme, it is more sensitive to processing and storage conditions than many vitamins and minerals. Some manufacturers therefore choose delayed-release capsules as part of their formulation approach.
For anyone whose interest in nattokinase started with circulation, the wider heart and circulation range covers nutrients with authorised claims in that area, and the same applies to lung health for those who arrived through the respiratory research. Anyone weighing up whether an enzyme supplement fits alongside what they are already taking can speak to our nutrition team, who are available to discuss general nutritional support.
Where the Evidence Currently Stands
Nattokinase is a well-characterised enzyme with a clear mechanism in laboratory conditions and an active research literature behind it. It also has no authorised health claims in the UK, and the human evidence remains limited.
That is a less satisfying answer than most articles on this ingredient will give, and being told the evidence is limited is frustrating when you are trying to decide whether to buy something. But an honest account of what is and is not known is more useful than a confident one that overstates it. Research is continuing, and the picture may change.
Anyone considering nattokinase, and particularly anyone taking medication that affects blood clotting, should speak to a doctor before starting.
Nattokinase FAQs
What does nattokinase do for the body?
Nattokinase is an enzyme that breaks down fibrin, a protein involved in normal blood clotting and tissue repair, in laboratory conditions. Research into what it does when taken as a supplement is ongoing. It holds no authorised health claims on the GB Nutrition and Health Claims Register in the UK.
Can nattokinase be taken every day?
Studies have generally used daily doses over set periods. Follow the directions on the label of any product taken, and note that the safety considerations above apply regardless of how long it is taken for.
What are the side effects of nattokinase?
Side effects reported in studies have generally been mild and gastrointestinal. The main concern is bleeding risk, given the enzyme’s fibrinolytic activity. Anyone experiencing unusual bruising or prolonged bleeding should stop taking it and seek advice from a doctor.
Is nattokinase suitable for people with a soy allergy?
No. Nattokinase is derived from fermented soybeans and is not suitable for anyone with a soy allergy.
Can nattokinase be taken alongside blood thinners?
Not without medical supervision. Anyone taking warfarin, aspirin, clopidogrel, a DOAC, or any other medication affecting blood clotting should speak to their doctor before taking nattokinase.
