Nattokinase supplement claims: what the trials really show

Nattokinase is an enzyme taken from natto, a Japanese dish of fermented soybeans, and the human evidence for it is thin and mixed: one small trial reported slightly lower blood pressure, while a 3-year trial of 265 people found no effect on artery thickness or blood pressure. If a sales page presents it as settled science for your heart or circulation, that is going further than the studies do.

This guide explains what the strange "FU" unit on labels means, what the main human trials actually measured, and what to check before you buy a product that lists nattokinase.

What is nattokinase, and what does FU mean on a label?

Nattokinase is a protein-digesting enzyme produced when soybeans are fermented with a bacterium to make natto. Supplement makers isolate it and sell it in capsules. Because it is an enzyme, the useful measure is not only its weight but its activity, and that is what FU (fibrinolytic units) describes.

The two numbers are not interchangeable. In one North American trial, the capsule was described as 100 mg of nattokinase standardized to at least 2,000 FU per daily dose. So "100 mg" and "2,000 FU" can describe the same capsule, but a label that gives only milligrams, or only a vague "nattokinase blend", does not tell you the activity. A product with many milligrams and low activity is not the same as one with fewer milligrams and high activity.

When you read a label, look for three things: the FU number per serving, whether it is per capsule or per daily serving, and whether nattokinase has its own line or is buried inside a group total.

What do the human trials actually show?

Most claims you see online trace back to a handful of studies. They differ a lot in size, length, dose and design, so they should not be blended into one "studies show" sentence. Here is a plain summary of the ones we could read.

Study	People and length	Dose	What it reported
North American blood pressure trial (Jensen and colleagues, 2016)	79 adults with elevated blood pressure, 8 weeks, 74 finished	100 mg a day (at least 2,000 FU)	Average diastolic pressure fell from 87 to 84 mmHg versus no change on placebo
Hemostasis trial (Yoo and colleagues, 2019)	100 adults with borderline to moderately high cholesterol, 8 weeks	Not listed in the abstract	Longer clotting-related times than placebo
Atherothrombotic prevention study (Hodis and colleagues, 2021)	265 adults, median age 65.3, median 3 years	2,000 FU a day	No difference from placebo in artery thickness, stiffness or blood pressure
Clinical study (Chen and colleagues, 2022)	1,062 participants, 12 months	10,800 FU a day, plus a lower-dose group	Authors reported improvements at the high dose and none at 3,600 FU

The pattern is not "it works" or "it does not work". It is that the results depend on the dose, the length and the design.

Why do the results disagree?

Look at the doses first. The 3-year placebo-controlled trial used 2,000 FU a day and found nothing on artery thickness or blood pressure. The larger 2022 report used 10,800 FU a day and described improvements, but also said 3,600 FU a day was ineffective. Its authors argued that the commonly recommended amount of 2,000 FU is too low, and they noted that daily doses across studies vary up to tenfold, from as low as 1,200 FU to 13,000 FU.

Now look at the design. The 2022 paper lists "retrospective study" among its own keywords, which matters: a retrospective analysis is weaker evidence than a randomized, double-blind trial that assigns people to placebo in advance. The 2021 trial was randomized and double-blinded, and it was the one that found no effect.

The honest reading is that nattokinase is still an open question. Small or short studies pointed one way, a longer randomized trial in healthy older adults pointed the other, and a supplement with a small dose cannot borrow results from a study that used a very large one.

What should you know about safety and blood thinners?

Nattokinase is studied for how it affects clotting, so the main practical caution is about medicines and procedures that also affect clotting. In the 8-week trial of 100 adults, the nattokinase group had longer collagen-epinephrine closure time and activated partial thromboplastin time than the placebo group. Those are lab measures of how quickly blood clots, and the authors described the finding as an association.

That is a reason to talk to a doctor or pharmacist before use if you take warfarin or another anticoagulant, take antiplatelet medicine, have a bleeding disorder, or have surgery coming up. A case report cited in the 2022 paper describes a patient with a mechanical heart valve who used nattokinase in place of warfarin and developed a clot, which is exactly the kind of substitution nobody should attempt on their own.

Nothing here is a reason to panic, and none of it means the ingredient is dangerous for everyone. It means an enzyme that acts on clotting is not a casual add-on when you are already on a blood thinner. Also remember that some nattokinase products are sold with vitamin K2 or other ingredients, which changes the questions to ask.

How do nattokinase claims show up in supplement offers?

The typical pattern is a video sales page that names a handful of "studied" plant ingredients, then hides the amounts. The Cardio Shield review is a clear example. Its label lists hawthorn, hibiscus, olive leaf, green tea, garlic and nattokinase inside a single 570 mg proprietary blend. We could not tell whether nattokinase gets a few milligrams or a few hundred, and with six plant ingredients sharing 570 mg in total, there is a limit to how much any one can hold. The review scored it 4.0 for evidence and 4.0 for transparency, and it credited the 180-day refund window as a real strength.

That is the trap: a blood pressure story assembled from real ingredient names can sound well supported while the finished product's dose stays unverifiable. Our review method treats a hidden dose as a transparency problem no matter how good the ingredient list sounds. You can also browse heart health offers to see how other products handle labels.

A short checklist before you buy a nattokinase product

1. Find the FU number per serving. If only "nattokinase" appears with no amount, treat the dose as unknown.
2. Check whether nattokinase has its own line or sits in a proprietary blend total.
3. Compare the label with the study the page cites: same dose, same length, same kind of participants?
4. Ask whether the cited study tested the finished product or only the ingredient.
5. Look at the refund terms before you enter your card. See the ClickBank refund guide for how refunds work on that marketplace.
6. If you take any blood thinner, have a bleeding condition or plan surgery, speak to your doctor or pharmacist first.

The goal is not to find a "perfect" product. It is to know what you are actually paying for and what a cited study did or did not measure.

FAQ

Is nattokinase the same as natto?

No. Natto is the whole fermented food. Nattokinase is one enzyme from it. One trial used a nattokinase product from which vitamin K2 had been removed, so the enzyme and the food are not the same thing.

How much nattokinase is in a typical capsule?

It varies. One trial used 100 mg with at least 2,000 FU, but published studies range from about 1,200 FU to 13,000 FU a day. A label that shows no FU figure cannot be compared with any of them.

Can I take nattokinase with a blood thinner?

Do not decide that on your own. An 8-week trial found longer clotting-related times in the nattokinase group, so ask your doctor or pharmacist before combining it with warfarin or similar medicines.

Does nattokinase lower blood pressure?

The evidence is mixed. One 8-week trial reported a small drop in diastolic pressure, and a 3-year trial reported no effect on blood pressure. Blood pressure that stays high needs medical care, not a supplement guess.