Nattokinase What the Evidence Shows, and the Bloods to Check First

1. What nattokinase is, and why it is trending

Nattokinase is an enzyme. It comes from natto, a sticky fermented soya dish eaten at breakfast in Japan. In a laboratory dish, the enzyme breaks down fibrin, the protein mesh that holds a blood clot together. That single lab property is the engine behind every claim you will read about it.

Interest has climbed steadily rather than spiked. Supplement forums have been busy this year with threads on nattokinase and its cousin lumbrokinase, mostly framed around blood flow. Long-COVID communities picked the topic up after some test-tube work on so-called microclots. Search interest in the UK has followed.

Doses are quoted in fibrinolytic units, written FU. The trials mostly used 2,000 FU a day at the low end, and 6,000 to 8,000 FU a day at the high end. A capsule on a UK shelf is usually 2,000 or 3,000 FU.

2. What the trials actually measured

The clearest human finding is on blood pressure, and it is modest. A 2023 systematic review and meta-analysis in Reviews in Cardiovascular Medicine pooled six randomised controlled trials covering 546 people. Systolic pressure fell by 3.45 mmHg against placebo. Diastolic pressure fell by 2.32 mmHg. Both results were statistically significant.

The trial most often quoted sits inside that pool. A 2008 randomised, placebo-controlled trial in Hypertension Research gave 86 adults 2,000 FU a day for eight weeks. Their starting systolic readings were 130 to 159 mmHg. The net fall was 5.55 mmHg systolic and 2.84 mmHg diastolic.

Put that in proportion. A 3 mmHg shift is real, but it is roughly what a decent walk most days or a lighter hand with the salt will do. The trials were small. Most ran for only eight weeks. None of them tracked whether anyone went on to have a heart attack or a stroke, so nothing here speaks to that.

A newer study may add something. A trial at Taipei Medical University (NCT07229521) began recruiting in March 2025. It is giving 6,000 FU a day for 12 weeks to 80 people with metabolic syndrome and poor sleep. Its main outcomes are sleep scores. Results are not published yet.

3. Does it do anything to your cholesterol?

On the evidence so far, no. This is the part the marketing tends to skip, and it matters most.

The same review looked at blood fats. At the low doses people actually buy, 1,200 to 2,000 FU a day for eight weeks, total cholesterol and LDL edged slightly up rather than down, and HDL edged slightly down. At high doses over longer periods, total cholesterol still crept up a little. Triglycerides did not move.

The authors put it plainly:

“Short-term and low-dosage ingestion of nattokinase might have no significant lipid-lowering effects.”

— Reviews in Cardiovascular Medicine, 2023 systematic review and meta-analysis

So the marker set that best predicts heart risk is untouched. If your worry is your arteries, a supplement that leaves your cholesterol numbers where they were is not answering the question you are asking. Our guide to which supplements earn their place applies the same test to the rest of the shelf.

4. The markers to check before you start

Here is the honest order of operations. Find out where your heart risk actually sits, then decide what, if anything, to take. The British Heart Foundation makes the case for measuring in one line:

“Most people with high cholesterol have no symptoms.”

— British Heart Foundation

You cannot feel any of this. Four markers carry most of the signal:

• ApoB — counts the harmful particles, rather than the fat inside them
• Lp(a)— set almost entirely by your genes, and usually worth measuring once in a lifetime
• hs-CRP — the standard marker of low-grade inflammation
• Your full lipid panel and HbA1c— the context that makes the other three readable

Our Advanced Heart Health panel (£159) measures all of them from a home finger-prick sample, analysed by UKAS-accredited UK laboratories. Blood markers describe risk. They cannot see plaque inside an artery, so a good result is a reassuring picture rather than an all-clear.

Two outcomes, both useful. Your numbers come back clean, and the worry that sent you shopping was unfounded. Or something is genuinely raised, in which case a qualified clinician and your GP have far better levers than an enzyme capsule. Either way you stop guessing. More on the wider marker set in our heart health hub.

5. The microclot claim, read honestly

Much of the current interest traces to one line of research. Teams at the University of Liverpool and Stellenbosch University have described fibrinaloid microclots, small amyloid-like fibrin structures seen in blood samples from people with long COVID and related conditions.

In a 2024 preprint, the same group added nattokinase to those structures in the laboratory and measured how they broke down under a microscope.

Read the design carefully, because it decides what the finding means. It was done in samples, not in people. No one swallowed anything. Nobody was followed to see whether symptoms changed. And at the time of writing it was a preprint, so it had not completed peer review.

The authors themselves describe the wider human evidence as largely anecdotal. So this is an interesting hypothesis with a laboratory result behind it. It is not evidence that taking nattokinase clears microclots, eases long COVID, or protects your arteries. Treat anyone who tells you otherwise with suspicion.

6. If you take a blood thinner, this is a GP conversation

This is the part of the story that deserves more attention than the benefits. The trials reported few side effects in healthy volunteers. The concern is not the enzyme on its own. It is the enzyme alongside medication that already affects clotting.

None of this makes nattokinase dangerous for a healthy adult taking nothing else. It does mean the decision belongs with your GP or pharmacist rather than with a forum thread.

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