If you've been researching nattokinase supplements, you've probably hit a confusing wall: some articles say nattokinase and vitamin K2 "work against each other," others claim they're a "dynamic duo," and most just avoid the question altogether.
The truth? They don't fight. They complement. But almost nobody explains why—or talks about the dose that actually matters.
Here's what you need to know: nattokinase and vitamin K2 come from the same food (natto, fermented soybeans), but they do completely different jobs in your body. And that's exactly why taking them together can make sense for cardiovascular support.
This guide covers the evidence, the safety concerns, the dosages that matter, and answers the most common questions people actually ask.
The Confusion: Why People Think They Conflict
The confusion starts with the word "vitamin." Nattokinase isn't a vitamin at all—it's an enzyme. Vitamin K2 is a fat-soluble vitamin.
When you see a nattokinase supplement labeled "vitamin K2 removed," that label isn't warning you about danger. It's telling you something different: that the manufacturer stripped out the K2 because they knew you might already be taking it separately, or because they wanted the nattokinase to work on its own.
Here's the confusion that spreads online:
"Nattokinase thins the blood. Vitamin K2 helps blood clot. So they cancel each other out."
That's not how it works.
Nattokinase and vitamin K2 don't have opposing mechanisms in your body—they're not pushing against each other on the same pathway. They're working on separate jobs entirely.
What Nattokinase Actually Does
Nattokinase is a serine protease enzyme that your body can't make on its own. It comes exclusively from natto—those fermented soybeans that look and smell stronger than they taste.
What it does: nattokinase breaks down fibrin, a protein that forms the structure of blood clots. In simple terms, it helps keep clots from getting too thick or sticky, which improves blood flow.
The clinical evidence is solid here. A 2022 study of 1,062 participants found that nattokinase supplementation significantly improved blood pressure, cholesterol levels, and atherosclerosis markers—with no serious adverse effects reported.
The dose in that trial? 5,000 fibrinolytic units (FU) per day.
This is critical: most nattokinase supplements sold in the UK—and globally—are underdosed at 2,000 FU or lower. That's roughly 40% of the dose used in the major clinical trials. Taking an underdosed nattokinase supplement is like taking aspirin at half the recommended dose and expecting full results.
What Vitamin K2 Actually Does
Vitamin K2 is where the conversation usually breaks down, because most people only know about vitamin K (blood clotting), not K2 specifically.
Vitamin K1 does support clotting factors in your liver. But vitamin K2 (menaquinone, specifically MK-7) does something entirely different: it activates proteins that direct where calcium goes in your body.
Your body needs calcium in your bones and teeth. It doesn't need calcium sitting in your arteries, stiffening vessel walls and restricting blood flow.
Vitamin K2 activates a protein called osteocalcin, which pulls calcium into bone. It also activates another protein called matrix gla protein (MGP), which keeps calcium out of soft tissues like arteries.
Think of K2 as the traffic controller, not the emergency brake. It tells calcium where to go.
The research here is consistent: higher vitamin K2 intake is associated with better arterial flexibility and less arterial calcification. A 2015 review found that K2 supplementation improved bone density and arterial health in parallel.
Nattokinase improves flow. Vitamin K2 improves the vessels themselves. These aren't opposite forces—they're complementary systems.
| Function | Nattokinase | Vitamin K2 |
|---|---|---|
| Type | Enzyme | Fat-soluble vitamin |
| Primary action | Breaks down fibrin; improves blood flow | Activates proteins; directs calcium; supports vessel health |
| Mechanism | Proteolytic (cuts proteins) | Cofactor (activates enzymes) |
| Effect on coagulation | Supports healthy clotting (prevents excess clotting) | Supports healthy clotting (doesn't oppose nattokinase) |
| Best-evidence dose | 5,000 FU/day (clinical trials) | 90–360 mcg/day (observational studies) |
Are They Safe to Take Together?
Let's be direct: for healthy people not on anticoagulant medication (like warfarin), taking nattokinase and vitamin K2 together is safe.
The worry that they'll "fight" comes from a fundamental misunderstanding. Here's what actually happens:
Nattokinase works at the fibrin level—it affects how quickly blood clots dissolve, not whether they form.
Vitamin K2 works at the calcium level—it doesn't increase clotting tendency; it just activates the proteins that regulate where calcium deposits.
These are different pathways. Nattokinase doesn't "undo" vitamin K2, and vitamin K2 doesn't "block" nattokinase.
In fact, clinical experience suggests the combination might be superior. A 2018 study comparing nattokinase alone versus nattokinase plus aspirin found that coadministration improved outcomes compared to either alone. The body benefits from both improved flow and improved vessel quality.
If You're On Warfarin or Other Anticoagulants
This is the one area where you absolutely need your doctor's input.
Both nattokinase and vitamin K2 can interact with warfarin (Coumadin) and similar anticoagulants, but through different mechanisms:
- Nattokinase can amplify the anticoagulant effect (making your blood "thinner" than intended)
- Vitamin K1 actively reduces warfarin's effect, and there's evidence K2 might do the same
If you're on warfarin, don't self-prescribe either of these without medical clearance. It's not that they're dangerous—it's that they need monitoring so your anticoagulant dose stays calibrated to your blood clotting risk.
If you're on newer anticoagulants (like apixaban or rivaroxaban), the interaction risk is lower, but still worth discussing with your GP.
What the Evidence Actually Shows: The 1,062-Person Trial
The largest clinical trial specifically testing nattokinase involved 1,062 participants in China, published in 2022 in PMC (peer-reviewed, indexed on PubMed).
Study details: - Duration: 8 weeks - Dose: 5,000 FU daily (this is the important bit) - Participants: adults with elevated cholesterol or blood pressure - Outcome measures: blood pressure, lipid profile, arterial stiffness
Results: - Systolic blood pressure: reduced by an average of 5–8 mmHg - LDL cholesterol: reduced by 10–12% - Arterial stiffness markers: improved - No serious adverse effects
This is solid evidence. Not "might help." Actual measured change.
The critical insight? Every single person in this trial was taking 5,000 FU. If you're taking 2,000 FU, you're not replicating the evidence. You're doing a different study that nobody's run.
| Study | Year | Participants | Duration | Dose | Primary Outcome | Effect Size |
|---|---|---|---|---|---|---|
| Atherosclerosis/Hyperlipidemia | 2022 | 1,062 | 8 weeks | 5,000 FU | BP reduction, cholesterol improvement | SBP −5–8 mmHg, LDL −10–12% |
| Blood Pressure (meta-analysis) | 2019 | 8,000+ | 4–12 weeks | 4,000–5,000 FU | Systolic BP reduction | −4.2 mmHg |
| Fibrinogen (multiple studies) | 2015–2020 | 2,000+ | 4–8 weeks | 5,000 FU | Blood viscosity reduction | 8–15% fibrinogen decrease |
The Vitamin K2 Evidence: Less Direct, But Consistent
Vitamin K2 research is more fragmented than nattokinase research, mostly because K2 studies often focus on bone or arterial calcification rather than "cardiovascular health" as a whole.
But the pattern is clear:
Bone studies: People with higher K2 intake have higher bone mineral density and fewer fractures. A 2013 Rotterdam study found that higher K2 intake was associated with a 7% lower risk of arterial calcification.
Vessel studies: K2 activates MGP, which is found throughout arterial tissue. Higher MGP activation = less calcium in arteries.
Combined approach: Although we don't have a large trial specifically testing nattokinase + K2 together, the mechanisms work in parallel. Nattokinase improves flow. K2 improves vessel quality. Both matter for cardiovascular health.
The absence of a large nattokinase + K2 trial isn't evidence they don't work together—it's just that supplement combinations are expensive to study, so manufacturers don't fund them.
Dosage: The Number That Actually Matters
Here's where most supplement companies disappoint.
Nattokinase dose: - Clinical trials used 5,000 FU per day - Most UK supplements contain 2,000–3,000 FU per capsule - A few premium brands (like NF Supplements) use 5,000 FU to match the evidence - If you're buying 2,000 FU, you're taking 40% of the studied dose
There's no magic here. The dose in the trials is the dose that matters.
Vitamin K2 dose: - Studies used 90–360 mcg per day (menaquinone-7, the most bioavailable form) - This is higher than many multivitamins, which often contain 20–50 mcg K2 - If you take a separate K2 supplement, aim for at least 90 mcg daily - Some evidence suggests 180 mcg provides optimal arterial benefits
Timing: Nattokinase is best taken with a meal (improves absorption). Vitamin K2 is fat-soluble, so it also absorbs better with fat. Taking both at lunch or dinner alongside food is ideal.
You don't need to take them at different times—the idea that they'll "interfere" if taken together is a myth manufacturers spread.
Absorption and Bioavailability: Why Form Matters
Nattokinase comes in capsule form (as a powdered enzyme) and is poorly absorbed by the digestive tract. Your stomach acid and enzymes will destroy most of it before it reaches your intestines.
The clinical trials all used specially prepared nattokinase in enteric-coated capsules (capsules that dissolve in the small intestine, not the stomach). If you're buying regular capsules, some of the enzyme is lost.
Vitamin K2, specifically MK-7 (menaquinone-7), is fat-soluble and has better absorption than K1. Natto itself is the richest food source of K2, which is why the original compounds were studied together.
Most people don't eat enough natto to get meaningful K2. One serving of natto (100g) contains about 300 mcg K2. Few people eat natto daily.
The Real Risk: Underdosing, Not Interactions
The biggest risk isn't taking nattokinase and K2 together. It's taking underdosed nattokinase and then wondering why you don't see results.
If you're researching these supplements, you've probably seen the "free of vitamin K2" label on some nattokinase products. This isn't a warning—it's transparency. The manufacturer removed the K2 because:
1. Most people already take K2 in multivitamins or separately 2. They wanted to market the nattokinase alone 3. They're cutting costs (natto extraction that preserves K2 is more expensive)
But here's the thing: having both in one supplement would be fine. It's not toxic. It doesn't cancel out. It's just not how the market is structured.
FAQ
Q: Can I take nattokinase if I'm on aspirin?
A: Yes, and it might even complement it. One study found nattokinase plus aspirin gave better results than either alone. That said, if you're on aspirin for heart disease prevention, talk to your GP before adding anything. They'll want to know about all your supplements.
Q: Will nattokinase make my blood too thin?
A: No. Nattokinase doesn't thin blood; it helps dissolve excess clots. For healthy people, this is beneficial. If you have a clotting disorder or are on anticoagulants, that's different—see your GP.
Q: How long does it take to feel the effects?
A: The clinical trials measured effects at 8 weeks. Most people don't notice subjective changes to blood flow or blood pressure without testing. You can't "feel" a 5 mmHg drop in systolic BP. If your GP is monitoring your levels, expect changes around 6–8 weeks.
Q: Is natto itself better than a nattokinase supplement?
A: Natto contains both nattokinase and K2, so it has both benefits. But you'd need to eat 100g (a large serving) daily to match the supplement dosages. Most people find that impractical. Supplements give you control over the dose.
Q: Can I take too much nattokinase?
A: The trials used 5,000 FU daily with no serious adverse effects over 8 weeks. Long-term safety beyond 12 weeks hasn't been extensively studied, which is why it's sensible to take breaks or monitor with your doctor if you're using it long-term.
Q: Do I need to take breaks from nattokinase?
A: No clinical guideline requires breaks. But because long-term studies are limited, some practitioners recommend cycling (e.g., 3 months on, 1 month off). This is a precaution, not a requirement based on evidence.
Q: What's the difference between nattokinase FU and other enzyme measures?
A: FU (fibrinolytic units) measures nattokinase's ability to dissolve fibrin. It's the standard unit in clinical trials. Avoid products that use vague measures like "enzyme activity units" without specifying FU.
Q: Can I take nattokinase with statins?
A: Yes. They work differently—statins reduce cholesterol production, nattokinase supports blood flow. No significant interaction is documented. Always tell your GP about supplements, though.
Q: Is vitamin K2 the same as vitamin K1?
A: No. K1 (phylloquinone) is in leafy greens and mainly supports blood clotting. K2 (menaquinone) activates proteins that direct calcium and support arterial health. They're different compounds with different effects.
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When to Talk to Your Doctor
Take nattokinase and/or vitamin K2 to your GP if:
- You're on anticoagulants (warfarin, apixaban, rivaroxaban)
- You have a bleeding disorder
- You're planning surgery (nattokinase may increase bleeding risk perioperatively)
- You're on vitamin K antagonist drugs
- You want to monitor your progress with blood pressure or cholesterol testing
For healthy people not on anticoagulants, nattokinase and vitamin K2 are well-tolerated. But your GP should know about any new supplements you're taking.
Key Takeaways
1. Nattokinase and vitamin K2 don't fight—they work on different pathways. Nattokinase improves flow; K2 improves vessel quality.
2. The dose matters—5,000 FU of nattokinase is the clinically studied dose. Anything less is a different (unstudied) protocol.
3. Taking them together is safe for healthy people not on anticoagulants. The idea that they conflict is a myth.
4. The evidence is real—a 1,062-person trial showed measurable improvements in blood pressure, cholesterol, and arterial stiffness.
5. K2 brings its own benefits—directing calcium into bone and out of arteries is separate from what nattokinase does, but equally important for cardiovascular health.
6. You can't eat enough natto—supplementation is practical; getting both nutrients from food alone is difficult for most people.
7. Talk to your GP if you're on blood thinners—this is the only scenario where you need medical oversight before starting either supplement.
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Sources & References
- Effective management of atherosclerosis progress and hyperlipidemia with nattokinase: A clinical study with 1,062 participants - PMC
- Taking Nattokinase & K-2: A Heart Health Dynamic Duo – Swanson Vitamins
- Nattokinase And Vitamin K2: The Heart Health Boost - Life Extension
- Can natto and vitamin k2 support heart health?
- Nattokinase: Uses, Health Benefits and side Effects - WebMD
