If you've spent any time on health TikTok or podcasts lately, you've probably heard someone talk about nattokinase. It's being sold as a natural way to "clean out your arteries," lower your blood pressure, prevent clots and even "detox" from COVID. Searches for it have more than doubled over the past year, and a lot of my patients are asking me about it.
I get why it sounds appealing. Nobody wants a stroke or a heart attack, and a supplement made from a traditional Japanese food sounds a lot gentler than a prescription. But this one deserves a closer look than most, because the thing that makes it interesting is also the thing that makes it risky.
What is nattokinase?
Natto is a sticky, stringy fermented soybean dish that's been eaten in Japan for centuries. It's an acquired taste, to put it kindly! In 1980, a Japanese researcher found that natto contains an enzyme that can break down fibrin, the protein that holds a blood clot together. That enzyme is nattokinase.
The supplements you see online are concentrated versions of that enzyme, usually labeled in "fibrinolytic units," or FU. The most common dose on the shelf is 2,000 FU per capsule.
What does the research actually show?
Here's the honest picture. Nattokinase clearly does something. In lab dishes and animal studies it breaks down clots, and in small human studies it changes some clotting markers in the blood. The question is whether that translates into fewer heart attacks and strokes for real people. So far, we don't know.
Blood pressure. A couple of small studies found modest drops in blood pressure after about eight weeks, roughly in the range of 3 to 5 points. That's real, but it's smaller than what you'd get from cutting back on salt or walking most days, and the studies were short with small groups of people.
Artery plaque. This is the big claim, and it's where the best study we have came up empty. A well designed three year trial in the United States gave 2,000 FU a day to healthy older adults and compared them to placebo. Nattokinase did not slow the thickening of their artery walls. One open label study from China using a much higher dose reported smaller plaques, but it didn't have a placebo group, and that's a big weakness.
Clots in the legs or lungs. There's no good evidence that nattokinase prevents or treats a deep vein thrombosis or a pulmonary embolism. None.
COVID and "spike protein detox." This is a lot of what's driving the current interest. A lab study showed nattokinase could break down the coronavirus spike protein in a dish. That's it. There are no human studies showing it clears anything from the body after an infection or a vaccine. A test tube is a long way from a person.
Why I'm cautious about this one
Most of the supplements I write about are pretty low risk. If magnesium doesn't help your sleep, you've mostly lost some money. Nattokinase is different, because it's designed to affect how your blood clots. When something does that, bleeding is the obvious concern.
There are published reports of people who took nattokinase along with aspirin or another blood thinner and ended up with bleeding in the brain. These are case reports, not big studies, but they're exactly what you'd predict from how the enzyme works.
Please don't take nattokinase without talking to your doctor first if you take any of these:
Warfarin (Coumadin)
Apixaban (Eliquis), rivaroxaban (Xarelto), dabigatran (Pradaxa) or another newer blood thinner
Clopidogrel (Plavix) or another antiplatelet medicine
Daily aspirin
High dose fish oil, which can add to the bleeding effect
And please talk to us before starting it if you have a bleeding disorder, liver disease, very low platelets, or a history of a stomach ulcer or bleeding in the brain.
Stop it ahead of any surgery or dental procedure, too. Most surgeons ask for about two weeks off. Let your surgeon know you've been taking it, since it isn't on the usual medication lists.
The biggest danger: swapping it for a prescription
This is the part I most want you to hear. I've seen people online say they stopped their Eliquis or warfarin and switched to nattokinase because it's "natural."
If you have atrial fibrillation, a mechanical heart valve, a recent stent or a history of blood clots, your blood thinner is protecting you from a stroke or a clot that could kill you. Nattokinase has never been tested as a replacement for those medicines. We have no idea what dose would protect you, if any would. Stopping your prescription for a supplement is a gamble I would never want you to take.
What about just eating natto?
Natto itself is a genuinely nutritious food. It's packed with protein and probiotics. It's also one of the richest sources of vitamin K2 on the planet, which is great for most people but a real problem if you take warfarin, because vitamin K works against it. If you're on warfarin and want to try natto, talk to us first so we can keep an eye on your levels.
Many nattokinase supplements have the vitamin K removed, but not all of them. Read the label carefully, and look for a USP or NSF seal, since supplements aren't checked the way medications are. People with a soy allergy should skip both the food and the supplement.
Things that do protect your heart and arteries
If what you really want is to lower your risk of a heart attack or stroke, we have tools with decades of evidence behind them:
Knowing your blood pressure and getting it under control
Checking your cholesterol and treating it when it's high
Not smoking or vaping
Moving your body most days
Eating more plants and less ultra processed food
Getting good sleep and treating sleep apnea if you have it
None of those are as exciting as a new supplement, but they work.
The bottom line
Nattokinase is an interesting enzyme with some early research behind it, and a lot of hype on top. The best trial we have didn't show it helps artery plaque, and there's no human evidence for the COVID detox claims. Because it affects clotting, it can be risky for people on blood thinners or aspirin, and it should never replace a prescription anticoagulant. If you're healthy and curious, talk to your doctor before you start it.
Want to talk through your heart risk?
At Homestead DPC, we have time to sit down with you and go over the whole picture, from your blood pressure and labs to every supplement in your cabinet. Bring the bottles in! We'll go through them together and figure out what's worth keeping. What's one supplement you've been wondering about lately?
Doc Langley
