Is Nattokinase Good for Kidneys? Potential Benefits Explained

Nattokinase shows kidney-protective effects in animal studies, reducing markers of inflammation, oxidative damage, and early kidney injury in rats and mice. But almost none of this research has been repeated in human clinical trials focused on kidney outcomes. The enzyme, originally isolated from the Japanese fermented soybean food natto, is best known for its ability to break down fibrin (the protein scaffolding of blood clots), and most human research has centered on cardiovascular health rather than renal function. So the honest answer is that nattokinase has plausible biological reasons to help kidneys, backed by several animal experiments, but calling it “good for kidneys” in humans requires a leap the evidence has not yet supported.

What Nattokinase Actually Is

Nattokinase is a fibrinolytic enzyme produced by the bacterium Bacillus subtilis natto during the fermentation of soybeans into natto, a sticky, pungent food that has been a staple in parts of Japan for centuries. Researchers first isolated and characterized the enzyme in the 1980s, and it has since been purified from various strains of the bacterium, all showing strong clot-dissolving activity.¹ Supplement manufacturers typically sell nattokinase in capsule form, measured in fibrinolytic units (FU), with common doses ranging from 2,000 to 4,000 FU per day. Some formulations specifically remove vitamin K2, which is naturally present in natto and can interfere with blood-thinning medications.

The enzyme works by directly degrading fibrin and by activating the body’s own clot-dissolving pathways. That fibrinolytic action is why most clinical interest has focused on blood clot prevention and cardiovascular disease. But kidneys are highly vascular organs, densely packed with tiny blood vessels, and conditions that damage those vessels (high blood pressure, diabetes, chronic inflammation) are the leading causes of kidney disease worldwide. That overlap is what makes researchers curious about whether nattokinase’s vascular benefits might extend to the kidneys.

Animal Studies Showing Kidney Protection

The strongest evidence for nattokinase’s kidney-related effects comes from rodent experiments, and there are now several showing measurable improvements in kidney biomarkers. These studies test different models of kidney damage, so it is worth looking at each type separately to understand what nattokinase appears to do and what remains uncertain.

Acute Kidney Injury From Inflammation

One of the more striking findings comes from a mouse study that induced acute kidney injury using bacterial toxins (LPS). Nattokinase protected against the kidney damage by restraining both inflammation and oxidative stress, which are tightly linked processes that amplify each other during acute injury.² The researchers framed this as breaking a “vicious loop” between inflammation, oxidative damage, and abnormal clotting, all of which feed kidney injury once they get started. The same study also showed nattokinase preventing ear swelling in mice (a standard inflammation test), reinforcing that the anti-inflammatory effect is systemic, not limited to one organ.

Radiation and Chemical-Induced Kidney Dysfunction

A different study looked at rats subjected to gamma radiation and then injected with isoproterenol, a chemical that stresses both the heart and kidneys. Nattokinase improved multiple markers of kidney status: kidney injury molecule-1 (KIM-1) improved by about 39%, a marker of oxidative damage (MDA) improved by roughly 59%, and inflammatory signaling through TNF-alpha in kidney tissue improved by about 18%.³ The study also found improvements in markers related to how the kidneys regulate blood pressure and fluid balance, including aldosterone and angiotensin-II levels. These are the same hormonal pathways that common blood pressure medications (ACE inhibitors and ARBs) target, which is interesting because those drugs are the frontline treatment for protecting kidneys in people with hypertension or diabetes.

Early Diabetic Kidney Changes

Diabetes is the single largest cause of chronic kidney disease globally, so whether nattokinase can slow diabetic kidney damage is a particularly relevant question. A study in rats with chemically induced diabetes found that nattokinase suppressed glycogen deposition in the kidney’s tubules, a hallmark of early diabetic kidney changes, in a dose-dependent manner. The high-dose nattokinase group also had significantly lower circulating levels of advanced glycation end products (AGEs), which are harmful compounds that accumulate in diabetes and directly damage kidney tissue. The control diabetic group had AGE levels roughly twice as high as healthy rats, while the nattokinase-treated group showed a meaningful reduction.⁴ Importantly, nattokinase did not lower blood sugar itself. The kidney-protective effects occurred independently of glucose control, which suggests the mechanism involves something other than simply fixing the underlying metabolic problem.

The same study tracked C-reactive protein (CRP), a broad marker of systemic inflammation. High-dose nattokinase significantly suppressed the CRP spike at day seven of treatment, though by day fourteen the levels had climbed back to match the control group.⁵ That partial and temporary anti-inflammatory effect is a useful reminder that animal results rarely translate into clean, permanent benefits. The kidney structural changes (glycogen deposition, AGE accumulation) improved more consistently than the inflammatory marker, which hints that multiple mechanisms are at play and some are more durable than others.

The Blood Pressure Connection

High blood pressure is both a cause and a consequence of kidney disease, and anything that meaningfully lowers blood pressure tends to slow kidney deterioration. This is where nattokinase may offer an indirect benefit even if it never touches the kidneys directly. A randomized, double-blind, placebo-controlled trial in North America found that nattokinase supplementation (specifically an extract called NSK-SD, from which vitamin K2 had been removed) was associated with reduced blood pressure and lower levels of von Willebrand factor, a marker tied to cardiovascular risk.⁶

More recent research has started to explain how nattokinase might lower blood pressure at a molecular level. When nattokinase is digested in the gut, it releases small peptides that inhibit angiotensin-converting enzyme (ACE), the same enzyme targeted by prescription ACE inhibitors like lisinopril and enalapril. Two newly identified peptides, called LGG and TW, showed potent ACE-inhibiting activity in laboratory tests, and computational modeling confirmed they bind stably to the enzyme.⁷ The researchers suggested that nattokinase-derived peptides could work through multiple cardiovascular targets simultaneously, not just ACE inhibition alone.

For kidney health specifically, the ACE-inhibition angle is intriguing. ACE inhibitors are prescribed to people with kidney disease precisely because they reduce pressure inside the kidney’s filtering units, slowing the progressive scarring that leads to kidney failure. If nattokinase produces similar peptides during normal digestion, it could provide a mild version of that same renal-protective effect. But “mild” is the key word here. The potency of a prescription ACE inhibitor and whatever ACE inhibition nattokinase might produce in a living person are almost certainly in different leagues. Nobody has measured the actual ACE-inhibiting peptide levels in human blood after taking a nattokinase supplement, so the real-world magnitude of this effect remains unknown.

Does It Actually Get Absorbed Well Enough to Matter?

A legitimate concern with any oral enzyme supplement is whether it survives digestion and reaches the bloodstream in meaningful quantities. Nattokinase is a protein, and the gut is in the business of breaking proteins into amino acids. Research on this front is moderately encouraging. A study using intestinal cell models and animal testing found that nattokinase is a “moderately absorbed biomolecule” that crosses intestinal cells through energy-dependent processes involving several different uptake pathways.⁸ “Moderately absorbed” is not the same as “highly bioavailable,” and it leaves open the question of how much active enzyme actually makes it into circulation after a typical supplement dose. Some of the benefit may come not from intact nattokinase reaching the kidneys but from the bioactive peptides released during digestion, as the blood pressure research suggests.

What About People Already on Dialysis?

People with advanced chronic kidney disease (CKD) face a different set of problems than those with early kidney damage. By the time someone is on hemodialysis, the kidneys have largely failed, and clotting management becomes a daily clinical challenge. Dialysis requires blood to flow through a machine, and heparin (a blood thinner) is routinely used to prevent the dialysis circuit from clotting. But heparin carries bleeding risks, and finding ways to use less of it while maintaining effectiveness is an active area of research.

One study investigated combining nattokinase with heparin for CKD patients on hemodialysis. The combination produced a synergistic increase in clotting time, both in laboratory tests and in animals, meaning the two agents together were more effective at preventing clots than either alone. The researchers also showed for the first time that nattokinase could degrade all three chains of fibrinogen (the precursor protein to fibrin), and that adding heparin markedly reinforced nattokinase’s clot-dissolving activity.⁹ The practical implication, if confirmed in larger clinical trials, would be that physicians could use lower heparin doses during dialysis sessions, reducing the bleeding risk that comes with full-dose heparin. This is a niche application, far from the general “is nattokinase good for kidneys” question, but it represents one of the few areas where nattokinase has been studied in the context of actual kidney disease patients rather than healthy animals.

Why You Should Not Replace Prescribed Medications

The enthusiasm around nattokinase in online health communities has occasionally led to dangerous decisions. A case report documented a patient who replaced their prescribed warfarin with nattokinase after receiving a mechanical heart valve. After nearly a year on nattokinase alone, the patient developed a blood clot on the prosthetic valve and required a second open-heart surgery to replace it.¹⁰ The authors explicitly stated that they strongly discourage using nattokinase as a substitute for warfarin in this context, and believed it was the first documented case of such a substitution.

This case carries a broader lesson for kidney patients. Many people with CKD take blood thinners, blood pressure medications, or both, and the idea that a “natural” supplement could replace those drugs is appealing but unsupported. Nattokinase does have measurable fibrinolytic and mild antihypertensive activity, but it has never been tested head-to-head against any prescription medication for kidney outcomes. Beyond replacement risk, there is also an interaction risk: taking nattokinase alongside anticoagulants like warfarin or direct oral anticoagulants could increase bleeding risk, since the effects on clotting would stack rather than substitute. If you are considering adding nattokinase to an existing medication regimen, particularly if you take blood thinners or have advanced kidney disease, talking to your nephrologist first is genuinely important.

Natto the Food Versus Nattokinase the Supplement

There is a meaningful difference between eating natto and swallowing a nattokinase capsule. Natto contains nattokinase, but it also contains vitamin K2 (menaquinone-7), soy protein, polyamines, and various other fermentation byproducts. Vitamin K2 promotes calcium deposition in bones rather than arteries, which has its own set of potential cardiovascular and even kidney-related implications. But vitamin K2 also counteracts warfarin, which is why supplement formulations marketed for cardiovascular use, like NSK-SD, specifically remove it.⁶

For kidney patients, the soy content in whole natto introduces another consideration. Soy is relatively high in phosphorus and potassium, two minerals that people with advanced CKD often need to restrict. A person on dialysis or with stage 4-5 CKD who starts eating large amounts of natto could worsen their electrolyte balance even if the nattokinase component were theoretically helpful. A purified nattokinase supplement sidesteps the phosphorus and potassium issue but also strips out whatever synergistic benefits the whole food might provide. Neither option has been properly studied in people with kidney disease, so the “which form is better for kidneys” question remains unanswerable with current evidence.

What Would Convince Researchers

The gap in the nattokinase-kidney story is not biological plausibility. Multiple animal studies point to anti-inflammatory, antioxidant, and anti-fibrotic effects in kidney tissue, and the blood pressure lowering mechanism through ACE-inhibitory peptides makes physiological sense. The gap is clinical validation. No randomized controlled trial has tested nattokinase as an intervention for any specific kidney disease endpoint in humans, such as slowing the decline of estimated glomerular filtration rate, reducing proteinuria (protein leakage in urine), or delaying the need for dialysis.

Animal models of kidney disease, while useful for generating hypotheses, have a notoriously poor track record of predicting human outcomes. Hundreds of compounds have shown kidney protection in rodents and then failed in human trials. Rats metabolize drugs differently, their kidneys have different susceptibility profiles, and the models used (chemical induction of diabetes, radiation exposure) do not perfectly mimic the slow, multifactorial progression of human kidney disease. The diabetic rat study’s finding that nattokinase reduced glycogen deposition and AGE levels is genuinely interesting, but the 14-day observation window tells us nothing about whether those effects persist or meaningfully change the trajectory of kidney disease over months or years.

What would be needed is a well-designed trial enrolling people with early-to-moderate CKD (ideally from diabetic or hypertensive causes, since those are the populations the animal data best apply to), randomizing them to nattokinase or placebo for at least a year, and tracking hard kidney outcomes. Until that trial exists, nattokinase’s kidney benefits remain in the category of “scientifically plausible but clinically unproven,” sitting alongside dozens of other supplements that showed promise in animals and never panned out in people.

Kidney Stones and Nattokinase

A common follow-up question is whether nattokinase affects kidney stone formation. Soy-based products sometimes raise concerns about oxalate content, since calcium oxalate stones are the most common type. Natto itself is not particularly high in oxalates compared to other soy foods, but the broader soy-oxalate connection exists. No study has directly examined whether nattokinase supplementation influences kidney stone risk in either direction. The enzyme’s anti-inflammatory properties could theoretically reduce the crystal-induced inflammation that contributes to stone growth, but this is speculation without supporting data. If you are prone to kidney stones, the standard advice about hydration, dietary oxalate management, and citrate intake is far better supported than adding any supplement.

One tangential area of research involves nattokinase’s relationship with calcium metabolism through vitamin K2, which is present in natto but typically removed from supplements. Vitamin K2 helps direct calcium toward bones and away from soft tissues, and some researchers have explored whether this could reduce vascular calcification in CKD patients, a serious problem in advanced kidney disease. But that research is about vitamin K2 specifically, not nattokinase. Conflating the two is a common error in online health discussions: natto the food contains both, but a nattokinase supplement with K2 removed offers none of those potential calcification benefits.