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Black Walnut

Other common name(s): black walnut hulls, English walnut, butternut, oilnut

Scientific/medical name(s): Juglans nigra

Description

The black walnut is a hardwood tree that grows widely in the United States, Canada, and parts of Europe. It can reach a height of more than 100 feet. The nut hulls, inner bark, leaves, and nut (also called the fruit) are used in herbal remedies.

Overview

Available scientific evidence does not support claims that that hulls from black walnuts remove parasites from the intestinal tract or that they are effective in treating cancer or any other disease. Early evidence from laboratory research suggests that juglone, a compound in black walnut, may have the potential to reduce cancer risk. However, studies in humans have not been done.

How is it promoted for use?

A small number of herbal medicine practitioners claim that cancer is caused by a parasite. Some of these practitioners claim that a tincture made from black walnut hulls, wormwood, and cloves will kill the cancer-causing parasites, preventing or curing the disease without causing significant side effects. Black walnut is claimed to effectively kill more than 100 types of parasites.

Black walnut is also promoted as a natural remedy for such wide-ranging conditions as acne, thyroid disease, colitis, eczema, hemorrhoids, ringworm, sore throats, tonsillitis, skin irritations, and wounds. Supporters claim black walnut hulls can be used as a mild laxative that eases general digestive problems. Because some people claim that it kills parasites in the stomach and intestines, they recommend black walnut for those who travel to areas with contaminated water supplies.

What does it involve?

One part of the black walnut tree used as a remedy is the hull of the fruit (the outside of the nut), which is harvested when it is green. Black walnut hull is available in tablets, capsules, and tinctures. However, some claim that only a tincture, a preparation in which the substance is mixed with alcohol, is effective. Some companies include powdered bark from the tree along with the hulls in their black walnut supplements.

The leaves of the black walnut tree are sometimes used to make tea or placed directly on affected skin to treat ringworm or other skin conditions. Black walnut leaves are available in capsules and tea bags. The inner bark can be used to make infusions, and is sometimes ground with the hulls.

What is the history behind it?

Ancient Greeks and Romans called black walnut fruit the "imperial nut" and reportedly used the hull to treat intestinal ailments. Black walnut has also played a part in Russian folk medicine since the seventeenth century. Throughout history, every part of the tree has been used in folk medicine to treat dozens of conditions, including the bite of a mad dog. According to traditional Chinese medicine, eating black walnuts builds physical strength. In Texas folk medicine, black walnut extract is considered an effective treatment for scorpion bites.

Today, craftspeople and artists prize the tree's fine-grained wood for making furniture and carvings, and the nuts are a safe and very popular food for people without nut allergies. Walnuts have been noted to contain omega-3 fatty acids as well as antioxidants such as folate and vitamin E.

What is the evidence?

Available scientific evidence does not support claims that black walnut hulls, bark, or leaves can cure or prevent any disease, including cancer. The notion that parasites cause cancer or that they can be killed with herbal remedies is also unsupported by the available scientific evidence.

Of interest, small studies in the lab have suggested that a compound called juglone, which is present in black walnut, may have some antitumor activity. However, studies have not been completed to find out if juglone can help prevent cancer in humans.

In addition, some studies in humans have suggested that eating walnuts (the nut itself, not the hull, leaves, or bark) can lower “bad” cholesterol and reduce the risk of heart disease. Most of these studies were done on the English walnut, a close relative of the black walnut. The study findings may not pertain to black walnuts.

Are there any possible problems or complications?

This product is sold as a dietary supplement in the United States. Unlike companies that produce drugs (which must be tested before being sold), the companies that make supplements are not required to prove to the Food and Drug Administration that their supplements are safe or effective, as long as they don't claim the supplements can prevent, treat, or cure any specific disease.
Some such products may not contain the amount of the herb or substance that is on the label, and some may include other substances (contaminants). Actual amounts per dose may vary between brands or even between different batches of the same brand. In 2007, the FDA wrote new rules to improve the quality of manufacturing for dietary supplements and the proper listing of supplement ingredients. But these rules do not address the safety of the ingredients or their effects on health.
Most such supplements have not been tested to find out if they interact with medicines, foods, or other herbs and supplements. Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects are not often available. Because of these limitations, any information on ill effects and interactions below should be considered incomplete.

In horses, black walnut wood or extract is known to cause a serious inflammatory disease called equine laminitis, which involves a buildup of white blood cells in the hooves, resulting in pain and lameness.

Because of the lack of research, little is known about the potential side effects of black walnut hulls or leaves in humans. However, allergy to tree nuts is common, and severe allergic reactions to walnuts have taken place. People who are allergic to other nuts, especially pecans, may also react to walnuts or walnut products. Note that black walnut is included as part of certain dietary supplements, so check ingredient lists carefully if you have allergies.

Relying on this type of treatment alone and avoiding or delaying conventional medical care for cancer may have serious health consequences.

Additional resources

More information from your American Cancer Society

The following information on complementary and alternative therapies may also be helpful to you. These materials may be found on our Web site (www.cancer.org) or ordered from our toll-free number (1-800-227-2345).

Dietary Supplements: What Is Safe?

The ACS Operational Statement on Complementary and Alternative Methods of Cancer Management

Complementary and Alternative Methods and Cancer

Placebo Effect

Learning About New Ways to Treat Cancer

Learning About New Ways to Prevent Cancer

References

Black walnut. Drug Digest Web site. Accessed at http://www.drugdigest.org/wps/PA_1_30G00GCIU0FI30I8HM8LAR3006/pages/common/ddPrintPage.jsp on April 4, 2011.

Black walnut. PDRhealth Web site. http://www.pdrhealth.com/drugs/altmed/altmed-mono.aspx?contentFileName=ame0211.xml&contentName=Black+Walnut. Accessed June 18, 2008. Content no longer available.

de la Rebière de Pouyade G, Riggs LM, Moore JN, et al. Equine neutrophil elastase in plasma, laminar tissue, and skin of horses administered black walnut heartwood extract. Vet Immunol Immunopathol. 2010 Jun 15;135(3-4):181-7.

Feldman EB. The scientific evidence for a beneficial health relationship between walnuts and coronary heart disease. J Nutr. 2002;132:1062S-1101S.

Kruger J, Savitsky K, Gilovich T. Superstition and the regression effect. Skeptical Inquirer. 1999;23:24.

McGuffin M, ed. American Herbal Products Association’s Botanical Safety Handbook. Boca Raton, FL: CRC Press; 1997.

Munday R, Munday CM. Induction of quinone reductase and glutathione transferase in rat tissues by juglone and plumbagin. Planta Med. 2000;66:399-402.

Olmedilla-Alonso B, Granado-Lorencio F, Herrero-Barbudo C, et al. Consumption of restructured meat products with added walnuts has a cholesterol-lowering effect in subjects at high cardiovascular risk: a randomised, crossover, placebo-controlled study. J Am Coll Nutr. 2008 Apr;27(2):342-8.

Pong AH. Tree nut allergies. Calgary Allergy Network Web site. http://www.calgaryallergy.ca/Articles/English/treenuthp.htm. Accessed April 4, 2011.

Sugie S, Okamoto K, Rahman KM, Tanaka T, Kawai K, Yamahara J, Mori H. Inhibitory effects of plumbagin and juglone on azoxymethane-induced intestinal carcinogenesis in rats. Cancer Lett. 1998;127:177-183.

Walsh T. Debunking the detoxification theory. Nutrition Forum. 1999;16:1.

Note: This information may not cover all possible claims, uses, actions, precautions, side effects or interactions. It is not intended as medical advice, and should not be relied upon as a substitute for consultation with your doctor, who is familiar with your medical situation.

Last Medical Review: 04/04/2011
Last Revised: 04/04/2011