Direct answer: Nattokinase is a protein-digesting enzyme produced by Bacillus subtilis during the fermentation used to make natto, a traditional Japanese soybean food. Supplements usually declare both the weight of the nattokinase preparation in milligrams and its laboratory-measured activity in fibrinolytic units (FU).
Commercial disclosure: The Health Improvers sells a nattokinase complex. The product example below uses our current label, while the scientific and legal statements are sourced independently.
Natto and nattokinase are related, but not identical
| Term | Meaning |
|---|---|
| Natto | A whole food made by fermenting cooked soybeans with Bacillus subtilis var. natto |
| Nattokinase | A serine protease enzyme produced during that fermentation |
| Nattokinase preparation | The concentrated ingredient used in a capsule or tablet |
| FU | An assay value used to express fibrinolytic enzyme activity under laboratory conditions |
Natto is sticky, strongly flavoured and eaten as food. A nattokinase capsule is not nutritionally equivalent to a serving of natto: the supplement isolates and standardises an enzyme preparation rather than supplying the whole fermented food.
Where did nattokinase come from?
Researchers reported a fibrin-digesting enzyme isolated from natto in 1987 and named it nattokinase. Later laboratory work characterised it as a serine protease produced by Bacillus subtilis strains.
Commercial ingredients are produced through controlled fermentation and processing. The exact production method, carrier materials and allergen status can differ between suppliers, so the finished product label—not the ingredient’s general origin—is the information that governs suitability.
Does nattokinase contain soy?
Nattokinase is commonly produced in a soy-based fermentation. Some highly processed ingredients may have different allergen specifications, but shoppers should never assume that fermentation removes the allergen. Check the finished product’s ingredients and allergen statement.
The Health Improvers Nattokinase Complex declares soy. Anyone with a soy allergy should not use it.
Is nattokinase vegan?
The enzyme can be produced through bacterial fermentation without animal-derived ingredients, but the complete product must still be checked. Capsule shells, processing aids and other formula ingredients determine whether a finished supplement is vegan. Our current product is labelled suitable for vegans.
Why are milligrams not enough?
Milligrams measure the weight of the nattokinase preparation. Enzyme preparations can differ in concentration, so equal weights do not necessarily have equal activity.
Many nattokinase labels therefore also use fibrinolytic units:
- 100mg tells you the preparation’s weight;
- 2,000 FU tells you the activity declared for that amount under the relevant laboratory assay.
FU should not be treated as a direct measure of clinical effect. It records performance in a test system, not an outcome in a person. If two suppliers use different activity methods or specifications, their numbers may not be perfectly comparable.
What does “standardised to 2,000 FU” mean?
It means the ingredient or serving is specified to provide an enzyme-activity result of 2,000 FU under the stated test method. It does not mean 2,000mg, and it does not mean that 2,000 FU is an officially recommended daily intake.
The amount has appeared in human studies, but results cannot be summarised as proof of benefit. For example, a 265-person randomized placebo-controlled trial using 2,000 FU daily found no significant effect on its measures of subclinical atherosclerosis, arterial stiffness, blood pressure or laboratory outcomes after a median of three years.
What is known about absorption?
Human pharmacokinetic evidence is limited. One pilot study involved 11 healthy participants after a single 2,000 FU dose and detected immunoreactive material in blood, but the authors said larger studies were needed. This small experiment does not establish a clinical benefit or an ideal dose.
What health claims are authorised?
Nattokinase has no authorised health claim in Great Britain. Sellers may describe what the ingredient is, how it is produced and how its activity is declared, but may not promise that a supplement prevents blood clots, improves circulation, lowers blood pressure or treats cardiovascular disease.
A complex may make authorised claims for qualifying vitamins or minerals. Those claims belong to the named nutrients, not to nattokinase.
Our label as a worked example
Each capsule of The Health Improvers Nattokinase Complex declares:
- 100mg nattokinase preparation;
- 2,000 FU enzyme activity;
- 55µg selenium, equal to 100% NRV;
- 5.5µg vitamin D, equal to 110% NRV;
- individually declared botanical ingredients;
- soy allergen information.
The directions state one capsule daily with water. The bottle contains 60 capsules. The formula’s authorised immune-system claims come from selenium and vitamin D; nattokinase itself carries no authorised health claim.
Frequently asked questions
Is nattokinase a probiotic?
No. It is an enzyme preparation, not a declared count of live microorganisms.
Is nattokinase the same as vitamin K2?
No. Natto food can contain vitamin K2, but nattokinase is an enzyme. Do not assume a nattokinase capsule supplies vitamin K2 unless the label specifically declares it.
Are FU the same as milligrams?
No. FU express measured enzyme activity; milligrams express weight.
Is 2,000 FU proven to work?
No. It is a quantity used in some human research and on many labels, not an authorised health claim, official recommended intake or guarantee of effectiveness.
Can I take nattokinase with medication?
Check the label and ask a pharmacist or doctor first—particularly if you use anticoagulant, antiplatelet or blood-pressure medicines. Never stop prescribed treatment to use a supplement.
How this guide was checked
Product facts were checked against our current label information on 3 August 2026. Scientific statements were checked against the original nattokinase report and published human studies indexed by PubMed. Claim wording was checked against current GOV.UK guidance and the GB claims register.
Sources
- PubMed: original 1987 report of nattokinase isolated from natto
- PubMed: pilot human pharmacokinetic study
- PubMed: randomized trial using 2,000 FU daily
- Department of Health and Social Care: GB Nutrition and Health Claims Register
- GOV.UK: nutrition, health claims and supplement labelling
Next, read how to compare nattokinase supplements and the nattokinase safety guide.
Always read the label and follow the directions. Food supplements are not a substitute for a varied and balanced diet and a healthy lifestyle. This article is general information, not medical advice.
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