http://en.wikipedia.org/wiki/Nattokinase

If this is working for you, as a blood thinner...I'd make sure you have testing for MGUS... Thick blood is a sign of potential cancers of the blood system. I think it should be diagnosed and watched.

Blood thinning runs some risks. We've seen in studies recently that one small baby aspirin 81mg can cause small brain bleeds in those taking it for cardiac protection. Up to 70% of people studied showed this alarming side effect.

If you suspect you have "poor" circulation", it might be a good idea to look at this method:
http://www.drignarro.com/

Also agents that reduce endothelial inflammation, which is small inflammatory changes in blood vessels' linings, may help. Bioavailable curcumin has a study showing benefit for this.
Also reducing homocysteine if elevated helps too.

There are only a few forms of curcumin that are readily absorbed. So choosing carefully, improves response.

Simply restoring magnesium to the body, if you are not eating magnesium rich foods, will improve blood flow as well.

Drugs that constrict blood vessels, can lead to poor circulation.
Cymbalta and Effexor are in that category, along with caffeine, and other stimulants. Hypothyroidism leads to cold extremities as well.