Blood pressure support is one of the most common reasons people start taking nattokinase.
But “supports healthy circulation” on a supplement label doesn’t tell you what was actually measured, in whom, or how consistently.
This guide walks through the actual clinical trials behind the claim, including a large study that found no effect at all, so you know exactly what the evidence does and doesn’t support.
Medical Overview
Nattokinase is a fibrinolytic enzyme derived from natto, a fermented soybean food. Its blood pressure research is separate from its more established fibrin-breakdown research, and the two shouldn’t be conflated.
The blood pressure findings below come from people who already had elevated blood pressure at the start of the study. This distinction matters, and it’s a point the research itself makes clear later in this guide.
Nattokinase is not a substitute for prescribed blood pressure medication, and anyone with diagnosed hypertension should continue their treatment plan and loop in their doctor before adding a supplement.
The Original Trial: Kim et al., 2008
The most frequently cited study on nattokinase and blood pressure is a randomized, double-blind, placebo-controlled trial published in Hypertension Research. Researchers enrolled 86 adults aged 20 to 80 with untreated systolic blood pressure between 130 and 159 mmHg — meaning pre-hypertension to stage 1 hypertension, not normal blood pressure.
Participants took 2,000 FU of nattokinase or a placebo daily for 8 weeks. Of the 86 enrolled, 73 completed the study. Compared with placebo, the nattokinase group showed a net reduction of 5.55 mmHg in systolic blood pressure and 2.84 mmHg in diastolic blood pressure. The study also measured plasma renin activity, an enzyme involved in blood pressure regulation, and found a corresponding decrease in the nattokinase group.
A Second Trial: Jensen et al., 2016
A separate randomized, double-blind, placebo-controlled, multicenter trial tested nattokinase specifically in a North American population, since the earlier research had focused on Asian populations. Researchers enrolled 79 adults with elevated blood pressure (systolic ≥130 or diastolic ≥90 mmHg), using a nattokinase extract with the vitamin K2 removed, at a dose of 100 mg (2,000 FU) daily for 8 weeks.
Seventy-four participants completed the study. Diastolic blood pressure dropped from an average of 87 to 84 mmHg in the nattokinase group, a statistically significant change compared to the placebo group, which stayed flat. The systolic reduction was seen in both sexes but was more pronounced in men. The study also tracked von Willebrand factor, a marker associated with clotting risk, and found a reduction in the nattokinase group.
What a Meta-Analysis Found
Individual trials can be affected by their specific population or design. A 2023 systematic review and meta-analysis pooled data from 6 randomized controlled trials totaling 546 participants to get a clearer picture across the available research.
The pooled analysis found nattokinase supplementation significantly reduced systolic blood pressure by an average of 3.45 mmHg and diastolic blood pressure by an average of 2.32 mmHg compared with placebo. The same analysis reported no notable adverse events across the included studies, though the authors noted the overall number of trials was still small and the findings should be interpreted with that limitation in mind.
The Important Exception: A 3-Year Trial Found No Effect
Not every nattokinase trial supports a blood pressure benefit, and leaving this out would be misleading. The longest randomized trial on nattokinase to date, the Nattokinase Atherothrombotic Prevention Study, followed 265 adults with a median age of 65 who had no clinical cardiovascular disease. Participants took 2,000 FU of nattokinase or placebo daily for a median of 3 years.
At the end of the study, there was no significant difference between the nattokinase and placebo groups in blood pressure, carotid artery thickness, arterial stiffness, or any laboratory measurement.
The distinction that reconciles this with the positive trials above appears to come down to baseline health. The trials that found a blood pressure benefit enrolled people who already had elevated blood pressure at the start. The 3-year trial enrolled healthy, low-risk adults with no cardiovascular disease. Taken together, this suggests nattokinase’s blood pressure effect, where it exists, may be most relevant for people who already have elevated readings — not something that lowers blood pressure further in people who are already in a healthy range.
How Might Nattokinase Affect Blood Pressure?
Researchers have proposed a few possible mechanisms, though none are fully settled. A review of nattokinase’s cardiovascular effects describes animal research showing that fragments produced when nattokinase is broken down can inhibit angiotensin-converting enzyme (ACE) activity, a pathway also implicated in dose-dependent blood pressure reduction observed in animal studies. Reduced renin activity, observed directly in the Kim et al. trial, is another proposed contributor, since renin plays a central role in the body’s own blood pressure regulation system.
What This Means If You’re Considering Nattokinase
If you have elevated blood pressure and are considering nattokinase, the clinical trials support a modest effect — in the range of a few mmHg — not a replacement for prescribed treatment. If your blood pressure is already well-controlled or in a normal range, the strongest available evidence (the 3-year trial) doesn’t show an additional benefit.
Because nattokinase also affects clotting activity, anyone on blood pressure medication, especially medication that also affects clotting, should talk to their doctor before adding it. This is covered in more depth in our guide to nattokinase and blood thinner interactions.
FAQs
Both trials that found a positive effect used 2,000 FU per day. This is covered in more detail in our nattokinase dosage guide.
Both positive trials measured results after 8 weeks of daily use, not a single dose. Blood pressure changes weren’t assessed sooner than that in these studies.
Not based on current evidence. The trials showing a benefit enrolled people with elevated blood pressure at baseline. A 3-year trial in healthy adults with normal cardiovascular risk found no blood pressure effect at all.
No. None of the available research positions nattokinase as a replacement for prescribed antihypertensive treatment. It should be discussed with a doctor as, at most, a potential addition — not a substitute.
This depends on the specific medication and your individual health profile, so it should be discussed with your doctor, particularly if you’re on any medication that also affects blood clotting.
The measured effects are modest — a few mmHg on average — rather than dramatic. Researchers describe them as statistically significant but not comparable to the effect of prescription antihypertensive medication.
Final Thoughts
The clinical picture on nattokinase and blood pressure is more nuanced than most product pages suggest. Two randomized trials in people with elevated blood pressure found modest, statistically significant reductions after 8 weeks. A pooled meta-analysis of 6 trials supports a similar effect size.
At the same time, the longest and largest randomized trial, run in healthy adults over 3 years, found no blood pressure benefit at all — a result worth knowing before assuming nattokinase will lower blood pressure across the board.
Anyone with diagnosed hypertension should treat nattokinase as a possible addition to discuss with their doctor, not a replacement for their current treatment.
If you’d like to compare specific nattokinase products, see our full guide: Best Nattokinase Supplements.