What Is Black Walnut?

Black walnuts come from the black walnut tree (Juglans nigra), which is native to North America. Black walnuts should not be confused with the more common English walnuts.

Because they grow on trees, black walnuts are tree nuts, a common allergen. Anyone with a tree nut allergy should avoid black walnuts.

Black walnut has long been used in complementary and alternative medicine. The kernels (or nuts) are thought to have anti-inflammatory, antibacterial, and antioxidant properties. Yet, research supporting these and other health claims for black walnut is lacking.

This article will discuss the potential uses of black walnut according to scientific evidence. It will also provide an overview of dosing, side effects, and precautions surrounding black walnut.

Uses of Black Walnut

Supplement use should be individualized and vetted by a healthcare professional, such as a registered dietitian, pharmacist, or healthcare provider. No supplement is intended to treat, cure, or prevent disease. 

Due to components such as monounsaturated fats, omega-3 fatty acids, and antioxidants, tree nut consumption has been linked to the prevention and treatment of various health conditions, including:

• Diabetes
• Heart disease
• Inflammation
• Cancer
• Neurodegenerative diseases

However, studies specific to black walnut for these and other purposes are scarce, and most studies have been performed in a lab or on animal models. There is not enough scientific evidence to support using black walnut for any health benefits in humans.

It's also worth noting that researchers are still investigating how to extract the active compounds from the black walnut effectively. Without proper extraction methods, black walnut supplements may not provide benefits at all.

Next is a look at some of the research on black walnuts.

Inflammation

Black walnut has been examined for its role in treating and preventing inflammation.

One lab study looked into black walnut extracts and their effects on inflammation in the body. Researchers found that compounds in black walnut inhibit the secretion of pro-inflammatory compounds in the body. These compounds were found in the kernel (nut) of the black walnut and included gallic acid, quercetin, and naringin, among others.

Other research has shown that the intake of nuts may improve inflammation. However, large-scale studies to confirm these effects have not been performed.

Antibacterial Properties

Some phytonutrients (plant compounds believed to promote health) in black walnut are thought to have antibacterial effects.

Research has shown that these phenolic compounds may disrupt the membrane structures of bacteria and inhibit their DNA synthesis.

One study investigated which components of black walnut may possess antibacterial properties. In the study, researchers examined 22 cultivars (varieties of cultivated plants) of black walnut and found that some exhibited antibacterial activity against Staphylococcus aureus (S. aureus). However, other cultivars were found to have no effects against S. aureus.

Heart Health

Higher nut consumption has been inversely associated with heart (cardiovascular) disease. Eating tree nuts two times per week has been linked to a lower risk of heart disease.

A small study compared the cardiovascular effects of black walnuts to those of English walnuts. For the study, participants ate about 1.06 ounces of either black walnuts or English walnuts every day for 30 days. Results showed that those who ate English walnuts experienced greater improvements in several measures of cardiovascular health compared to those who ate black walnuts.

Other research suggests that black walnuts may provide as much nutritional value, if not more, than English walnuts or other types of tree nuts. As some scientists have pointed out, more research is necessary on the effects of black walnut on heart health.

What Are the Side Effects of Black Walnut?

Black walnuts are generally considered safe for those without tree nut allergies. Consuming black walnuts in reasonable food amounts is thought to pose little risk. However, side effects may be possible, especially when using black walnut supplements.

Common Side Effects

Due to a lack of research, little is known about the safety of long-term use of supplements containing black walnut extract.

There is anecdotal evidence of digestive issues, like diarrhea and stomach pain, caused by using black walnut. However, these and other possible side effects are not documented in studies or reviews.

Only use black walnut supplements as directed to prevent potential adverse events.

Severe Side Effects

As a tree nut, black walnuts may not be safe for everyone. If you have a tree nut allergy, consuming black walnuts or using black walnut supplements may cause a serious allergic reaction.

Both children and adults can have tree nut allergies. When an allergy is present, consuming tree nuts may cause asthma, watery eyes, runny nose, eczema, edema (swelling), and anaphylaxis. Anaphylaxis is a serious, even life-threatening condition.

If you suspect you may have a tree nut allergy, talk with a healthcare provider about getting properly diagnosed.

Precautions

Black walnut supplements are not appropriate for everyone. Certain people must take extra precautions, while others should avoid taking black walnut altogether.

There is not enough evidence to know if black walnut supplements are safe for people who are pregnant or breastfeeding. It's best to play it safe and avoid black walnut supplements during these life stages. However, black walnut is likely safe when consumed in amounts normally found in foods.

Safety tests for black walnut supplements have not yet been performed on children. Additionally, evidence is lacking regarding the safety of black walnut supplements for people with various health conditions.

Finally, anyone with a tree nut allergy should avoid using black walnut.

If you're considering using black walnut for a health condition, consult a healthcare provider first. And remember that supplements should not replace standard medical care.

Dosage: How Much Black Walnut Should I Take?

Currently, there are no recommended dosage guidelines for black walnut supplements. This is because there is not enough reliable evidence supporting black walnut as a medicine or treatment for any health condition.

As a food, black walnuts are consumed in varying amounts. A typical serving of nuts is about 1 ounce (equal to a small handful).

If you decide to use black walnut supplements, follow the dosing recommendations as listed on the product label. Or, consult a healthcare provider regarding proper dosing for you.

What Happens If I Take Too Much Black Walnut?

When consumed as food or in supplement form, black walnut is not considered toxic to humans.

There is some concern about a substance called juglone, which is found in the hulls (outer covering) of black walnuts. It is thought that juglone may produce reactive oxygen species, which are unstable molecules that may be harmful. Interestingly, though, juglone may also act as an antioxidant.

More safety studies are needed on black walnut, but black walnut has not been reported as toxic.

Interactions

Black walnut may interact with various medications, herbs, and supplements.

Black walnuts contain substances called tannins that have antioxidant potential. These tannins may interact with certain medications.

Tannins are thought to be complex structures that may increase the risk of interactions. Some research shows that tannins may interact with anticoagulants (blood thinners) and medicines used to treat malaria. Yet, these interactions are not well understood.

It should be noted that there are no documented interactions for black walnut. More research is needed.

Before choosing a new supplement, carefully read the ingredients list and nutrition facts panel to learn which ingredients are included. It's important to review supplement labels with your healthcare provider to discuss any potential interactions with foods, other supplements, and medications. 

How to Store Black Walnut

Black walnuts and black walnut supplements should be stored in a cool, dry place. They should also be stored in their original container and kept out of direct sunlight.

Black walnut supplements and extracts typically do not require refrigeration. Be sure to follow storage instructions as written on the product label. Some people recommend refrigerating whole black walnuts.

Keep black walnut supplements out of reach of small children and pets.

Discard black walnuts and black walnut supplements once they reach their expiration date.

Similar Supplements

Black walnut has been researched for various health benefits. These potential health benefits are similar to those of many other herbs and supplements.

Supplements that may work similarly to black walnut include:

• Bromelain: Found in the stem of pineapples, bromelain has been touted as a natural remedy for inflammation. According to one lab study, bromelain may alter the inflammatory response. In the study, bromelain successfully reduced inflammation in cells from the gastrointestinal tract.
• Thyme: Studies have shown that thyme, a common spice, may be antibacterial. One study that looked at a range of essential oils found thyme essential oil to have some of the strongest antibacterial activity. However, research on thyme is still in the early stages.
• Quercetin: Quercetin is a substance found naturally in many plants that may be useful in the treatment and prevention of heart disease. Quercetin contains flavonoids (antioxidants) that are thought to improve hypertension (high blood pressure), inflammation, and other aspects of heart disease.
• Lycopene: Lycopene is a carotenoid, a type of plant pigment with known antioxidant properties. As an antioxidant, lycopene may fight off potentially harmful free radicals, protect DNA, and reduce oxidative stress.

If you're interested in trying these or other supplements, talk with a healthcare provider about which ones are best for you.

Sources of Black Walnut & What to Look For

It's always best to take a food-first approach to nutrition. This means eating whole black walnuts is recommended over black walnut supplements. Whole foods tend to contain more nutrients and benefits than dietary supplements.

Food Sources of Black Walnut

Black walnuts may not be as easy to find in stores as English walnuts, but they are available for purchase online.

You can find black walnuts in their raw, whole form and still in the shell. Chopped and shelled black walnuts are also available.

Black walnuts can be eaten alone or added to various cooking and baking recipes.

Black Walnut Supplements

Black walnut supplements are often in the form of tinctures and essential oils. You may also find black walnut supplements in capsule form.

Often, black walnuts are paired with other ingredients and nutrients when sold as a dietary supplement. Be sure to read the full ingredients list on the supplement label before choosing a brand.

Vegan, gluten-free, and/or organic black walnut supplements are available. These and other details should be listed on the nutrition label or product packaging of the supplement.

Recall that dietary supplements are not regulated in the United States. Supplements that have been reviewed and approved by third-party agencies tend to be of better quality than those that have not. Look for black walnut supplements with a seal from NSF, USP, ConsumerLab, or another third party.

Summary

Black walnuts come from the black walnut tree and may have anti-inflammatory, antibacterial, and antioxidant properties However, there is very little research on the potential health benefits of black walnuts and black walnut supplements.

Generally, it's best to take a food-first approach to get the nutrition you need, so consider consuming black walnuts as food before opting for their supplement form. A typical serving of nuts is about 1 ounce.

If you're considering black walnut supplements, talk with a healthcare provider to ensure it's the right choice.