Nattokinase

Despite its name, nattokinase is not a kinase but an extracellular serine protease closely related to subtilisin, produced by Bacillus subtilis during the fermentation that turns boiled soybeans into natto ^[1]. The purified enzyme is a single chain of roughly 275 amino acids and digests fibrin, the protein meshwork that gives blood clots their structure ^[1]. It was originally isolated directly from natto but can now be manufactured by fermentation and recombinant methods, and many other Bacillus-fermented legume foods contain nearly identical proteases ^[1].

Interest in nattokinase centers on the cardiovascular system. In the test tube and in animals it shows strong fibrinolytic activity, both cutting fibrin directly and inactivating plasminogen activator inhibitor-1 (PAI-1), a molecule that normally restrains clot breakdown ^[1][2]. Human trials are fewer and less consistent. A randomized, controlled trial in adults with elevated blood pressure reported modest reductions in systolic and diastolic pressure after eight weeks of supplementation ^[3]. By contrast, a larger multi-year randomized trial in people at low cardiovascular risk found no effect of nattokinase on the progression of subclinical atherosclerosis or on blood pressure ^[4]. Reviews describe it as a promising but not yet proven cardiovascular agent ^[5].

Nattokinase is sold over the counter as an oral capsule, often standardized in fibrinolytic units (FU). A recurring scientific question is whether the intact enzyme survives digestion and reaches the bloodstream in an active form; evidence on oral bioavailability remains limited and debated ^[5]. Because of its effect on clotting, it is generally cautioned against in people taking blood thinners or approaching surgery. It is regulated as a food supplement rather than an approved medicine.

The main concern is increased bleeding risk, especially when combined with anticoagulants, antiplatelet drugs, or before surgery. It is generally well tolerated otherwise, with occasional GI upset. People with bleeding disorders or on blood thinners should avoid it or use only under medical supervision.