Cathy Wong is a nutritionist and wellness expert. Her work is regularly featured in media such as First For Women, Woman's World, and Natural Health.

Emily Dashiell, ND, is a licensed naturopathic doctor who has worked in group and private practice settings over the last 15 years. She is in private practice in Santa Monica, California.

Nattokinase is an enzyme extracted from nattō, a popular Japenese breakfast dish made from fermented soybeans. Nattō has long been used in folk medicine to treat cardiovascular diseases; nattokinase is believed to possess the same properties.

Nattō, known for its strong, cheese-like smell and sticky consistency, is made by adding the bacterium Bacillus subtilis natto to boiled soybeans and leaving it until fermented. The only source of nattokinase is nattō, and it can only be produced using this specific fermentation process.

The extracted enzyme is manufactured into capsules and tablets, although it can also be found in powdered form in Japan. While generally considered safe and tolerable, nattokinase may cause side effects and interact with certain medications.

In alternative medicine, nattokinase is believed to benefit people with heart and vascular diseases, in part by breaking down blood clots that can impede circulation. Among the conditions nattokinase is purported to prevent or treat are:

To date, there are few studies that strongly support these claims. That is not to say that promising research doesn't exist; it is simply that most of the studies are small and often poorly designed. Here are a few worth considering.

Deep vein thrombosis is the medical term used to describe a blood clot in a deep vein, usually a leg. It tends to affect older people who are obese and have underlying circulatory problems.

A 2015 study published in Scientific Reports notes that a single 100-milligram (mg) oral dose of nattokinase was able to break down fibrin—a protein involved in blood clotting—more effectively than a placebo. It also acted as a potent anticoagulant (blood thinner), reducing the concentration of a blood-clotting protein known as factor VIII.

The research suggests that nattokinase supplements may provide protection against DVT by preventing the formation of clots.

While the results are promising, the conclusions are limited by the small size of the study. Moreover, the participants recruited for research (12 healthy young men) are in a demographic that is among the least likely to develop DVT. Further research would be needed to see if the same results can be replicated in higher-risk groups.

Atherosclerosis, also referred to as the hardening of arteries, is caused by the buildup of fatty plaques on the arterial walls.

A 2018 study from China involving 76 adults with atherosclerosis reported that participants given a 150-mg daily dose of nattokinase over 26 weeks experienced a 36.6% reduction in arterial plaque compared to only 11.5% in those given a 20-mg dose of simvastatin. Additionally, nattokinase increased the level of "good" HDL cholesterol, though simvastatin did not.

However, simvastatin was far more effective in reducing total cholesterol, triglycerides, and "bad" LDL cholesterol, reductions of which are vital to the prevention of cardiovascular disease.

As contradictory as these findings seem, they highlight how little scientists understand the mechanism of action of nattokinase. Further research is needed to identify how nattokinase works and its implication in preventing heart attacks, stroke, and other conditions related to atherosclerosis.

Cardiovascular disease and brain health are closely linked. In recent years, there have been suggestions that nattokinase may have neuroprotective properties that halt disease progression in people with ischemic stroke.

A 2015 study in the journal Stroke reported that nattokinase, given by injection, may improve blood flow to the brain following a stroke. By injecting lab mice with three doses of nattokinase prior to an induced stroke, scientists found that smaller vessels in the brain remained unblocked, limiting the spread of tissue damage. Confirming a similar effect in humans requires additional research.

The ability to break down fibrin (referred to as fibrinolysis) makes nattokinase an ideal candidate for research—not only with respect to stroke but other conditions influenced by fibrinolysis impairment, including Alzheimer's disease.

As a derivative of nattō, nattokinase is presumed to be safe. But that doesn't mean that it is without concerns.

Because nattokinase can influence blood circulation and chemistry, it should be used with caution in certain groups, namely:

Nattokinase should also be stopped no less than two weeks prior to a scheduled surgery to reduce the risk of excessive bleeding.

Due to the lack of research, nattokinase should be not be used in children or during pregnancy or breastfeeding.

There is little data as to the long-term effects of nattokinase.

In the United States, nattokinase is found almost exclusively in capsule or tablet form. Doses are often indicated in fibrin units (FU), with 2,000 FU translating to roughly 100 milligrams (mg) and 3,000 FU translating to 150 mg.

There are no universal guidelines for the appropriate use of nattokinase. Doses of up to 3,000 FU have been used safely for up to 26 weeks, although most manufacturers recommend no more than 2,000 FU per day.

In addition to supplements, you can also obtain nattokinase by adding nattō to your diet. There are small producers in the United States who ship fresh nattō directly to consumers and health food stores. You can also make your own by purchasing Bacillus subtilis natto spores online.

Nattō offers some advantage over nattokinase supplements in that it is rich in probiotic bacteria beneficial to gut health.

Nattō is also high in fiber and delivers over 20% of the recommended daily intake of iron, magnesium, calcium, vitamin C, and potassium.

On the downside, a one-cup serving of nattō has around 371 calories. That is not exceptionally high but accounts for nearly one-fifth of a 2,000-calorie diet. If you choose to consume natto, its caloric content should be accounted for in your daily consumption.

Because dietary supplements are not strictly regulated in the United States, the quality can vary from one brand to the next.

To ensure quality and safety, choose brands that have been tested by an independent certifying body like the U.S. Pharmacopeia (USP), ConsumerLab, or NSF International. The certification does not mean that the product is effective but that it simply contains the ingredients listed on the product label in the indicated amounts.

If purchasing Bacillus subtilis natto spores, opt for those that are 100% organic and sourced from a reliable retailer. You should also that check that Bacillus subtilis or Bacillus subtilis natto is printed on the product label to ensure you are getting the correct product.

How can I make nattō? The process of making fresh nattō involves the following 10 steps. Before you begin, be sure that you sterilize all of equipment you will use by dipping it in a pot of boiling water.

When does nattō expire? Nattō can be stored for up to one week in the refrigerator and up to two months in the freezer.

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Kurosawa Y, Nirengi S, Homma T, et al. A single-dose of oral nattokinase potentiates thrombolysis and anti-coagulation profiles. Sci Rep. 2015;5:11601. doi:10.1038/srep11601

Ren NN, Chen HK, Li Y, McGowan GW, Lin YG. A clinical study on the effect of nattokinase on carotid artery atherosclerosis and hyperlipidaemia. Zhonghua Yi Xue Za Zhi. 2017 Jul 11;97(26):2038-42.

Ahn YJ, Kim MH, Kim J, et al. Abstract W P262: Neuroprotective effect of nattokinase mediated by inhibition of platelet aggregation and thrombosis in photothrombotic stroke. Stroke. 2015;46(Suppl 1):AWP262.

Ren NN, Chen HJ, Li Y, et al. A clinical study on the effect of nattokinase on carotid artery atherosclerosis and hyperlipidaemia. Zhonghua Yi Xue Za Zhi. 2017 Jul 11;97(26):2038-2042. doi:10.3760/cma.j.issn.0376-2491.2017.26.005.

Bell V, Ferrão J, Fernandes T. Nutritional Guidelines and Fermented Food Frameworks. Foods. 2017 Aug;6(8):65. doi:10.3390/foods6080065.

FoodData Central. Natto. Updated April 1, 2019.

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