G'day Joe,
Nattokinase has sort of come to a dead end. Big pharma can't make money out of it as it is a "natural" product so there is no money around for large scale studies of it. We can only rely on very small scale studies and here say which is not good enough.
Personally I won't touch nattokinase supplements as I don't trust the different manufactures of it. Also I think there are more enzymes in natto food that work in concert with nattokinase that do the clot busting and blood thining rather than singling out only nattokinase.
I have now been eating natto food every second day for 18yrs. My GP doctor is now a natto convert too. He puts it in a blender and drinks it!! Yuk.
Here is a link to the side effects of eating natto:
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superfoodly.com]
Dean