When women first hear that nattokinase comes from natto, a traditional Japanese fermented soybean food, one question often comes up immediately:

Does nattokinase contain estrogen?

It is an understandable question. Soy is well known for naturally occurring compounds called isoflavones, which are often referred to as phytoestrogens because they can interact weakly with estrogen receptors.

But nattokinase and soy isoflavones are not the same thing.

Nattokinase is an enzyme produced during the fermentation of soybeans with Bacillus subtilis. It is not estrogen, and nattokinase itself is not classified as a phytoestrogen.

Researchers characterize nattokinase as a fibrinolytic serine protease, an enzyme studied primarily for its interactions with fibrin and other aspects of cardiovascular and circulatory health.

That distinction matters, especially for women navigating hormone changes, menopause, cardiovascular concerns, or conditions such as endometriosis.

So, what do we actually know about nattokinase, estrogen and women's health, and where is the research still developing?

First: Does Nattokinase Contain Estrogen?

No. Nattokinase is not estrogen.

Estrogen is a group of steroid hormones naturally produced by the human body, with estradiol being the predominant form during the reproductive years.

Nattokinase, by contrast, is a protein-digesting enzyme produced during natto fermentation.

The confusion generally comes from the fact that nattokinase originates from fermented soybeans.

Whole soy foods contain naturally occurring isoflavones, including genistein and daidzein. Because their chemical structures allow them to interact with certain estrogen receptors, these compounds are commonly called phytoestrogens.

But the enzyme nattokinase itself is not a soy isoflavone or a hormone.

Does Nattokinase Increase Estrogen?

This is where the answer becomes more nuanced.

Current clinical research on nattokinase has focused primarily on:

• Fibrinolytic activity
• Blood coagulation factors
• Blood pressure
• Vascular health
• Cardiovascular biomarkers

There is currently not enough clinical research to conclude that nattokinase meaningfully increases or decreases estrogen levels in women.

In other words:

Nattokinase does not contain estrogen, and there is currently no established evidence showing that nattokinase supplementation raises estrogen levels.

That does not mean researchers have definitively proven that nattokinase has no interaction with every hormonal pathway. It simply means hormonal effects have not been established as a known mechanism of nattokinase.

Why Circulation Becomes Especially Important for Women With Age

While nattokinase itself may not be a hormone supplement, hormones and circulation are closely connected.

That relationship becomes particularly important during perimenopause and menopause.

Estrogen does more than influence menstruation and reproductive health. Estrogen signaling also interacts with the cardiovascular system, including the cells lining our blood vessels.

One of the key players is the endothelium, the thin layer of cells lining the inside of blood vessels.

A healthy endothelium helps vessels respond appropriately by widening or narrowing as blood flow demands change.

Research suggests that estrogen helps support endothelial function through several mechanisms, including nitric oxide signaling and regulation of oxidative stress and inflammatory pathways. As estrogen declines during menopause, some of this vascular protection may decline as well.

Researchers have observed that changes in endothelial function may accelerate during the menopausal transition, particularly during late perimenopause.

That makes circulation an important, and sometimes overlooked, part of women's healthy-aging conversations.

Menopause Is Not Just About Hot Flashes

When most of us think about menopause, we tend to think about symptoms such as:

• Hot flashes
• Sleep disruptions
• Mood changes
• Weight changes
• Vaginal dryness
• Changes in skin and hair

But changes are happening inside the cardiovascular system too.

Before menopause, women generally have lower cardiovascular disease rates than similarly aged men. That advantage narrows with advancing age and the menopause transition.

Researchers believe declining estrogen is one contributor, although menopause involves a much more complicated shift involving estrogen, progesterone, FSH, LH, testosterone, metabolic health, aging and other factors.

Vascular aging can involve changes such as:

Greater Arterial Stiffness

Arteries may gradually become less flexible with age.

Reduced Endothelial Function

Blood vessels may become less responsive to signals telling them to widen.

Changes in Nitric Oxide Availability

Nitric oxide helps blood vessels relax and supports healthy blood flow.

Increased Oxidative Stress

Oxidative stress is one mechanism researchers associate with age-related endothelial dysfunction.

These changes help explain why women's heart and vascular health deserves increasing attention through the 40s, 50s, 60s and beyond.

Where Does Nattokinase Fit Into Women's Circulation Research?

Nattokinase has received scientific attention because of its fibrinolytic activity.

To understand why, it helps to understand fibrin.

Fibrin is a protein your body produces during the normal blood-clotting process. When you are injured, fibrin helps create a mesh that stabilizes a clot so bleeding can stop.

Once that clot is no longer needed, the body's fibrinolytic system helps break fibrin down.

This balance between forming clots and breaking them down is an essential part of normal physiology.

Research has shown that nattokinase can interact with fibrin and several pathways involved in fibrinolysis, which is why researchers have continued investigating the enzyme in the context of cardiovascular health.

In one small human study involving healthy adults, people with cardiovascular risk factors and dialysis patients, two months of nattokinase consumption was associated with changes in fibrinogen and coagulation factors VII and VIII. The study included both men and women but was not designed specifically around women's hormonal health.

Another randomized North American trial studied nattokinase in adults with elevated blood pressure.

Interestingly, researchers observed a reduction in elevated von Willebrand factor in a subgroup of female participants. However, the authors specifically noted that larger studies are needed to understand whether factors such as age, menopause, birth control use and hormone replacement therapy influence nattokinase's effects in women.

That point is important.

Women are included in some nattokinase research, but women's health deserves much more targeted research.

What About Nattokinase and Menopause?

There is currently no strong clinical evidence showing that nattokinase:

• Increases estrogen
• Replaces estrogen
• Treats menopause
• Corrects hormonal imbalances
• Relieves menopausal symptoms directly

And we would not position it that way.

The more scientifically appropriate connection is circulatory wellness.

As women move through menopause, healthy lifestyle habits that support the cardiovascular system become increasingly important.

That includes:

• Regular movement
• Resistance training
• Maintaining healthy blood pressure
• Eating a nutrient-dense diet
• Avoiding smoking
• Managing metabolic health
• Getting adequate sleep
• Maintaining regular preventive care

Some women may also choose to incorporate nutrients or supplements associated with cardiovascular wellness into this broader routine.

Nattokinase is one such ingredient being studied.

Nattokinase and Endometriosis: Why Do These Searches Often Overlap?

Another common search question is whether nattokinase can help women with endometriosis.

The connection usually comes back to one word:

Fibrin.

Endometriosis is a complex, estrogen-responsive inflammatory disease in which tissue similar to the uterine lining grows outside the uterus.

Inflammation, fibrosis, scar tissue and adhesions can all play roles in the disease process.

Because fibrin is involved in wound healing and adhesion formation, and because nattokinase is known for its fibrinolytic activity, nattokinase is sometimes discussed online as a "systemic enzyme" for women with endometriosis.

However, there is a very important distinction:

Nattokinase has not been established in clinical trials as a treatment for endometriosis.

Research demonstrating nattokinase's ability to influence fibrin or fibrinolytic pathways should not automatically be interpreted to mean that taking nattokinase will break down endometriosis lesions or adhesions inside the body.

Those are very different claims.

Endometriosis is a complex medical condition that can involve hormones, immune signaling, inflammation, fibrosis, pain pathways and multiple organ systems.

Anyone who has, or suspects they may have, endometriosis should work with a qualified healthcare professional rather than attempting to treat the condition with supplements alone.

That said, the overlap between endometriosis and nattokinase searches makes sense scientifically. Women researching fibrin, fibrosis and adhesions frequently encounter discussions of fibrinolytic enzymes.

The key is separating what scientists know about the enzyme from what has actually been demonstrated in women with endometriosis.

Can Women Take Nattokinase During Perimenopause or After Menopause?

Being female, perimenopausal or postmenopausal is not by itself a contraindication to nattokinase.

In fact, postmenopausal women have participated in nattokinase cardiovascular research.

But whether nattokinase is appropriate for a particular woman depends much more on her health history and medications than her hormonal stage alone.

Women should speak with their healthcare provider before using nattokinase if they:

• Take anticoagulant or antiplatelet medications
• Take daily aspirin
• Have a bleeding or clotting disorder
• Have a history of deep vein thrombosis or significant clotting problems
• Have an upcoming surgery or medical procedure
• Take multiple cardiovascular medications
• Are pregnant or breastfeeding
• Have a medical condition requiring ongoing treatment

Nattokinase may affect normal clotting processes, so people using medications that influence clotting should discuss supplementation with their healthcare professional first.

Can You Take Nattokinase With Hormone Replacement Therapy?

Women using menopausal hormone therapy may understandably wonder about this as well.

There currently is not enough high-quality research specifically studying nattokinase together with hormone replacement therapy to make broad assumptions about safety for every patient.

An absence of a documented interaction is not the same as proof that a combination is appropriate for everyone.

This is especially important because decisions around menopausal hormone therapy can involve a woman's individual cardiovascular risk, clotting history, age, route of estrogen administration, other medications and personal medical history.

If you use estrogen, progesterone or another form of hormone therapy, it is best to show your complete supplement list to the healthcare professional managing your treatment before adding nattokinase.

What About Younger Women?

Circulation is not only a concern after menopause. Women of any age benefit from supporting cardiovascular health. Some of the simplest strategies are also among the most valuable.

Move Every Day

• Walking is one of the easiest ways to encourage healthy circulation.
• Add structured cardiovascular exercise and strength training when possible.

Break Up Long Periods of Sitting

Many of us spend hours working at a desk which negatively impacts circulation and for many causes back and hip pain.

• Standing, stretching or walking periodically gives your body a reason to keep moving throughout the day. Aim for once an hour. If possible every 30 minutes. Even a 30-60 second stretch can help a lot!
• If possible, try a standing desk. You can raise it up and down periodically throughout the day. It's also great to do after lunch to aid with digestion.

Eat for Vascular Health

• Build meals around vegetables, fruit, legumes, whole grains, nuts, seeds and other minimally processed foods.
• Traditional Japanese dietary patterns also incorporate foods such as vegetables, sea vegetables, soy, tea and fermented foods.

Do Not Ignore Blood Pressure

High blood pressure often has no obvious symptoms. Knowing your numbers becomes increasingly important as you get older.

Protect Your Sleep

Sleep, metabolic health and cardiovascular health are closely connected. Treat sleep as part of your wellness routine rather than an afterthought.

A Japanese Tradition Meets Modern Women's Wellness

Natto has been eaten in Japan for centuries.

Traditionally made by fermenting soybeans with Bacillus subtilis, natto develops its distinctive texture, flavor and nattokinase enzyme during fermentation.

At Crane Wellness, we have taken inspiration from this traditional Japanese food and created a concentrated daily formula for modern wellness routines.

Crane Wellness Nattokinase Blend provides 6,000 FU of nattokinase per serving alongside three additional ingredients rooted in Japanese wellness:

Okinawa Moromi Vinegar

A traditional vinegar derived from the fermentation process used to create Okinawan awamori.

Aomori Garlic Extract

Made from garlic sourced from Aomori Prefecture, a region of Japan known for producing premium garlic.

GABA

A naturally occurring amino acid involved in signaling within the nervous system.

The formula is made in Japan and designed to make nattokinase easy to incorporate into a consistent daily wellness routine.

The Bottom Line: Nattokinase, Estrogen and Women

Women's wellness deserves more than oversimplified answers.

Here is what we currently know:

Nattokinase is not estrogen.

Nattokinase itself is not a phytoestrogen.

There is currently no established evidence that nattokinase supplementation raises estrogen levels.

Research on nattokinase has primarily focused on fibrinolysis and cardiovascular markers rather than female hormone regulation.

Menopause can influence vascular health, making circulation increasingly important as women age.

Nattokinase is sometimes discussed in connection with endometriosis because of fibrin and fibrosis, but it has not been clinically proven to treat endometriosis.

Perhaps most importantly, healthy aging is not about treating cardiovascular health, hormonal health, brain health and metabolic health as completely separate systems.

They interact.

For women approaching or moving through menopause, supporting healthy circulation through movement, nutrition, preventive healthcare and consistent lifestyle habits can be one meaningful part of supporting the body through decades of change.

Support Your Daily Circulation Routine

Discover Crane Wellness Nattokinase Blend 6,000 FU, made in Japan with nattokinase, Okinawa Moromi Vinegar, Aomori Garlic Extract and GABA.

Shop Nattokinase Blend →

Important Safety Note

Nattokinase may affect blood clotting. Individuals taking anticoagulant, antiplatelet or blood-thinning medications, including daily aspirin, or those with bleeding or coagulation disorders should speak with a healthcare professional before taking nattokinase. Nattokinase should not replace medication or medical treatment prescribed by your healthcare provider.

This article is for educational purposes only and is not intended to diagnose, treat, cure or prevent any disease.