Does nattokinase work against blood clots and for your heart?

Nattokinase can break down fibrin (the threads that make up blood clots) in the laboratory, and the enzyme also acts on thrombin, a key protein in blood clotting. In mouse studies, the formation of tail thrombosis fell by 42%. That sounds impressive, but animal research does not always translate into the same effects in humans.

The truly decisive question is: does nattokinase also work in a living human being? A large, well-designed randomised trial with 265 older adults gives the clearest answer. After an average of three years of taking 2,000 FU of nattokinase daily, nobody showed any benefit compared with the placebo group. Arterial hardening, blood pressure, blood clotting, blood fats and inflammatory markers: on not a single endpoint was there a measurable difference. That is a null result across virtually everything nattokinase is promoted for.

An additional practical problem is that the enzyme does not tolerate the acidic environment of the stomach well. Whether enough active enzyme actually reaches the bloodstream after swallowing a capsule has not been demonstrated in humans. Laboratory scientists are developing variants that are more stable, but these have not yet been tested in clinical trials.

On the safety side, no serious side effects were reported in the large RCT over three years. However, people who are already taking blood thinners (such as warfarin) or who have an elevated bleeding risk have barely been studied. Do not therefore combine nattokinase with blood thinners without first discussing it with your doctor.