Long COVID and ME/CFS research has increasingly focused on “fibrinaloid microclots,” an abnormal, amyloid-like form of fibrin that resists normal clot-dissolving processes and is thought to obstruct capillary blood flow, potentially explaining some of the fatigue, brain fog, and exercise intolerance reported by patients. Because nattokinase is a well-characterized fibrin-degrading enzyme, it has drawn attention as a possible tool against these microclots specifically, separate from its more established cardiovascular research. This article covers what the actual laboratory evidence shows, and where it stops.
Key Takeaways
- Fibrinaloid microclots are an abnormal, amyloid-form fibrin structure identified in Long COVID and ME/CFS patients that resists normal fibrinolysis.
- A 2024 study from University of Liverpool and Stellenbosch University researchers found nattokinase effectively degrades these microclots in vitro, with a half-life to noticeable clot reduction of roughly two hours.
- A separate 2022 study found nattokinase degrades the SARS-CoV-2 spike protein on infected cell surfaces in a dose- and time-dependent manner.
- Both findings are laboratory (in vitro) research. No controlled clinical trial has tested nattokinase as a treatment for Long COVID or ME/CFS symptoms in patients.
What Fibrinaloid Microclots Are
Researchers Resia Pretorius and Douglas Kell have described a mechanism in which fibrinogen polymerizes into an abnormal, amyloid-like form during or after certain infections, creating microclots that are structurally different from normal fibrin and resistant to the body’s usual fibrinolytic machinery. These fibrinaloid microclots have been identified at elevated levels in Long COVID and ME/CFS patients, and the working hypothesis is that they obstruct the smallest capillaries, potentially starving tissue of oxygen and contributing to fatigue and cognitive symptoms.
The 2024 Degradation Study
A 2024 study developed an automated microscopic method to quantify fibrinaloid microclot formation and kinetics, then tested recombinant nattokinase’s ability to break them down. The enzyme degraded the microclots effectively in vitro, with a half-life to noticeable clot reduction of approximately two hours, and both tested doses (14 ng/µL and 28 ng/µL) were effective without over-digesting the sample, suggesting a workable dosing window in the lab model[1]. The researchers themselves characterized the broader therapeutic case for nattokinase in Long COVID as still resting largely on anecdotal patient reports layered on top of this laboratory data, explicitly calling for controlled clinical trials.
The Spike Protein Angle
A separate line of research examined whether nattokinase could degrade the SARS-CoV-2 spike protein itself. When cell lysates expressing the spike protein were incubated with nattokinase, the protein was degraded in a dose- and time-dependent manner, and immunofluorescence imaging confirmed degradation of spike protein present on the cell surface[2]. This matters to the Long COVID discussion because persistent spike protein, whether from residual viral reservoirs or circulating fragments, is hypothesized by some researchers to be a driver of ongoing endothelial inflammation. This study, like the microclot work, was conducted in cell culture, not in Long COVID patients.
What This Doesn’t Establish
Two in vitro findings, however mechanistically interesting, are not the same as a clinical trial showing that oral nattokinase supplementation reduces microclot burden or improves symptoms in Long COVID or ME/CFS patients. Oral nattokinase must survive digestion and reach the bloodstream in active form to have any systemic fibrinolytic effect, a bioavailability question that hasn’t been specifically tested for microclot degradation in living patients. Anyone with Long COVID or ME/CFS considering nattokinase for this reason should discuss it with a physician familiar with their case, particularly given the drug interaction and bleeding-risk profile nattokinase already carries for cardiovascular use, and should not treat the current evidence as equivalent to a proven therapy.
References
- Kruger A et al. Automated microscopic measurement of fibrinaloid microclots and their degradation by nattokinase, the main natto protease. bioRxiv preprint (2024). bioRxiv
- Tanikawa T et al. Degradative Effect of Nattokinase on Spike Protein of SARS-CoV-2. Molecules (2022). PMID 36080170
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