Nattokinase is an enzyme from natto, a fermented soya bean dish traditional in Japan. In recent years it has attracted interest as a nattokinase supplement, and researchers have studied it for blood flow and blood pressure. In this guide we cover what nattokinase is, what the research found, how much nattokinase per day is used, and what to check before you buy in the UK.
For dosage timing, see our guide: Best Time to Take Nattokinase — Morning or Night?.
What Is Nattokinase?
Nattokinase (NK) is a serine protease enzyme first identified in 1987 by Dr Hiroyuki Sumi at the University of Chicago, who was studying traditional Japanese foods for fibrinolytic (fibrin-breaking) activity. He found that natto, the sticky fermented soybean food eaten widely in Japan, contained an enzyme with strong activity against fibrin in the laboratory.
Fibrin is the protein mesh that forms part of a blood clot. Animal and small human studies suggest some nattokinase is absorbed after it is swallowed. A 2024 systematic review and meta-analysis of randomised controlled trials looked at nattokinase and several cardiovascular risk markers (systematic review and meta-analysis, PubMed); the trials it pooled were small and used different doses.
In supplement form, nattokinase is standardised in Fibrinolytic Units (FU) — a measure of enzymatic activity rather than weight. This lets you compare products: two capsules with the same milligrams can have very different FU.
What Does a Nattokinase Supplement Do?
In laboratory studies, nattokinase breaks down fibrin directly. Researchers have also looked at whether it affects the body's own plasminogen activator system, which clears fibrin naturally. These are findings from studies, not proven effects of taking a supplement, and nattokinase has no authorised health claims in the UK.
What Does the Research Say?
Human trials have looked at three things: blood clotting markers, blood flow and blood pressure. The results are mixed.
- Clotting markers. Short studies of 2 to 8 weeks measured changes in fibrinogen and other clotting factors after nattokinase. These were small trials, often without a placebo group.
- Blood pressure. An 8-week randomised controlled trial in 86 adults with raised blood pressure found a small fall in blood pressure compared with placebo (Kim et al., Hypertension Research, 2008).
- Long-term use. The longest trial to date gave 265 healthy adults 2,000 FU of nattokinase or a placebo for a median of 3 years. It found no significant effect on artery wall thickening, blood pressure or any of the laboratory measures, including clotting factors (Hodis et al., 2021).
Nattokinase is a food supplement. It is not a treatment for high blood pressure or any heart or circulation condition, and it should never replace prescribed medicine.
Stimulant-Free — No Caffeine, No Synthetic Compounds
Nattokinase contains no stimulants, synthetic blood thinners or pharmaceutical compounds. It is a single enzyme made from a fermented food.
How Much Nattokinase Per Day?
The question of how much nattokinase per day is one of the most common questions from new users — and the answer depends on the strength of the supplement you choose, measured in Fibrinolytic Units (FU).
Studies have used doses from 2,000 FU to 10,000 FU per day. The amounts used most often are 2,000–6,000 FU per day:
- 2,000 FU per day — the dose used in the longest (3-year) trial
- 4,000 FU per day — used in several shorter trials
- 6,000 FU per day — the highest amount commonly used in studies
Our NutritionGo nattokinase supplement provides 6,000 FU per capsule. The label serving is 1 to 2 capsules a day, on an empty stomach. Start with 1 capsule a day and do not take more than the label serving.
Nattokinase and Vitamin K2
Natto, the fermented soybean food nattokinase comes from, is also naturally rich in vitamin K2 in the form menaquinone-7 (MK-7). The two are different things: nattokinase is an enzyme, while vitamin K2 is a vitamin. A nattokinase supplement does not have to contain vitamin K2, and many, including ours, have it removed.
Does our nattokinase contain vitamin K2?
No. Our nattokinase capsules are vitamin K2-free. Each capsule provides 6,000 FU of nattokinase and no added vitamin K.
Why vitamin K2 matters if you take warfarin
Vitamin K contributes to normal blood clotting, and warfarin works by blocking it. That means extra vitamin K2 can make warfarin less effective. MK-7 stays in the blood for a long time, and researchers have warned that supplements providing 50 micrograms a day or more may interfere with anticoagulant treatment (Schurgers et al., Blood, 2007). In a later study, as little as 10 micrograms a day changed how volunteers responded to a warfarin-type medicine (Theuwissen et al., 2013).
Can you take nattokinase and vitamin K2 together?
Many people who do not take blood thinners buy nattokinase and vitamin K2 as separate supplements and take them together. There are no studies on the combination, and they work in different ways: vitamin K contributes to normal blood clotting and to the maintenance of normal bones, while nattokinase is an enzyme that acts on fibrin. If you want vitamin K2, check the amount in micrograms on the label. Speak to your GP or pharmacist first if you take any regular medicine.
Read more about natto and its vitamin K2 in our guide to nattokinase foods, and about bleeding risk in nattokinase side effects.
Nattokinase Supplement UK — What to Look For When Buying
Not all nattokinase supplements are equal. Here's what to check before buying:
Potency in FU — not milligrams
Always buy nattokinase measured in Fibrinolytic Units (FU), not milligrams. Milligram weight tells you how much powder is in the capsule — it tells you nothing about enzymatic activity.
FU stated per serving
Most studies used at least 2,000 FU a day. A product that does not state its FU content cannot be compared with the research or with other products.
Vegan and free from fillers
Traditional nattokinase is derived from fermented soybeans and is naturally vegan, though some products use gelatin capsules — check the capsule shell material if you follow a plant-based diet.
UK-made with transparent sourcing
Choose a supplement manufactured in a GMP-compliant UK facility with clear ingredient sourcing, as potency can degrade during storage.
Some people take nattokinase alongside CoQ10 or omega-3. Check with your pharmacist if you take any medicine.
Who Should Not Take a Nattokinase Supplement?
Nattokinase is broadly well tolerated by healthy adults but is not suitable for everyone:
- Anyone taking blood thinners — warfarin, aspirin, clopidogrel, heparin or any anticoagulant medication. The combination can increase bleeding risk.
- Anyone scheduled for surgery — stop nattokinase at least 2 weeks before any surgical procedure.
- Pregnant or breastfeeding women — insufficient safety data exists for these groups.
- People with bleeding disorders — including haemophilia or any condition causing abnormal clotting.
- People taking blood pressure medication — nattokinase may lower blood pressure and could interact with antihypertensive drugs.
What happens when you start taking nattokinase?
Most people don't notice anything when they start. Take it on an empty stomach, as food can reduce enzyme absorption. If you bruise easily or notice unusual bleeding, such as nosebleeds or bleeding gums, stop taking it and speak to your GP. Studies measured changes in blood markers over 2 to 8 weeks, but there is no authorised claim that you will feel a difference.
Nattokinase is part of our wider heart-health and circulation range. It also fits our circulation support range.
The bottom line
Nattokinase is a stimulant-free enzyme from natto, studied for blood flow and blood pressure with mixed results, and with no authorised health claims in the UK. If you buy it, look for a clearly stated FU rating, take no more than the label serving, and check with your GP before combining it with blood-thinning or blood-pressure medication.
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