Consumption of nattokinase is associated with reduced blood pressure and von Willebrand factor, a cardiovascular risk marker: Results from a randomized, double-blind, placebo-controlled, multicenter North American clinical trial 

From 2016 this randomized, double-blind, placebo-controlled, parallel-arm clinical study was performed to evaluate nattokinase (NSK-SD), a fermented soy extract natto from which vitamin K2 has been removed.  Authors found that consumption of nattokinase was associated with a reduction in both systolic and diastolic BP. The reduction in systolic BP was seen for both sexes but was more robust in males consuming nattokinase.   

References:

Jensen GS, Lenninger M, Ero MP, Benson KF. Consumption of nattokinase is associated with reduced blood pressure and von Willebrand factor, a cardiovascular risk marker: results from a randomized, double-blind, placebo-controlled, multicenter North American clinical trial. Integr Blood Press Control. 2016 Oct 13;9:95-104. doi: 10.2147/IBPC.S99553. PMID: 27785095; PMCID: PMC5066864. https://pubmed.ncbi.nlm.nih.gov/27785095/