“Nattokinase, an enzyme produced in natto, can help people recovering from COVID-19 or Long COVID by breaking down fibrinogen scar tissue and substantially lowering the risk of cardiovascular disease." (Transcript wording: "If you're somebody who has microvascular issues or... if you have received the COVID shot, experienced COVID or long…”

The strongest cardiovascular evidence is the NAPS randomized controlled trial. In this double-blinded trial, 265 individuals of median age 65.3 years without clinical evidence of cardiovascular disease were randomized to oral nattokinase 2,000 fibrinolytic units or matching placebo, with the primary outcome being rate of change in subclinical atherosclerosis measured by serial carotid ultrasound. After a median 3 years of randomized treatment, annualized rate of change in carotid intima-media thickness and carotid arterial stiffness did not significantly differ between nattokinase and placebo, and there was no significant effect of nattokinase on blood pressure or any laboratory determination. The authors concluded that nattokinase supplementation has a null effect on subclinical atherosclerosis progression in healthy individuals at low risk for cardiovascular disease. The 2023 meta-analysis reached a limited conclusion. Across 607 participants, it found nattokinase might have a beneficial influence on blood pressure, but no significant improvements were observed in blood lipids or blood glucose, and the total number of studies examining any cardiovascular risk factor was small. The same review also notes a trial in healthy subjects where nattokinase showed no detectable effects on any observed coagulation and fibrinolytic factor, such as prothrombin time, activated partial thromboplastin time, von Willebrand factor antigen and tissue plasminogen activator antigen, at 1 week and 1, 3, and 6 months relative to placebo. On COVID-specific mechanisms, the evidence is laboratory-based. In one study, cell lysates transfected with SARS-CoV-2 spike protein were incubated with nattokinase and the spike protein was degraded in a dose-dependent manner. A separate laboratory study examined Long COVID-type microclots: nattokinase is described as a protease with fibrinolytic activity that can degrade conventional blood clots, and in some cases, including Long COVID, fibrinogen can polymerise into an anomalous amyloid form. The authors of that work were explicit about the state of the field: the work "adds to the otherwise largely anecdotal evidence, that we review, that nattokinase might be anticipated to have value as part of therapeutic treatments for individuals with Long COVID". Note the conditional framing ("might be anticipated") and the acknowledgement that supporting human evidence is anecdotal. No completed randomized trial of nattokinase in COVID-19 or Long COVID patients was found. A 2025 review of the literature by a nattokinase-sympathetic blogger reports that there have been no more recent studies looking at nattokinase treatment for Long Covid, though at least one clinical trial is exploring similar systemic proteolytic enzymes for long COVID symptoms. Clinical summaries state that there is currently no conclusive scientific evidence that curcumin, N-acetylcysteine, or nattokinase effectively treat long COVID symptoms or address its underlying causes. The "spike detoxification" framing traces to a specific origin. Science Feedback documented that the claim circulated after a Substack post citing an August 2022 study reporting that nattokinase can break down spike protein, which was then screenshotted and spread on social media. The protocol itself is a proposal, not a trial result: its authors state that findings on spike protein persistence "give support to the potential benefit of spike protein detoxification protocols" and that they "propose a base spike detoxification protocol, composed of oral nattokinase, bromelain, and curcumin". That is a hypothesis-generating proposal, not evidence of efficacy. One finding of patient-reported data exists but is not a trial: a PNAS survey of patient-reported treatment outcomes in ME/CFS and long COVID reported that nattokinase/lumbrokinase improved three core symptoms in roughly 38 to 50 percent of respondents, with some benefit reported in POTS, in the context that thrombotic sequelae and microclotting have been investigated in long COVID. Self-reported, uncontrolled survey data cannot establish efficacy.