Black walnut (Juglans nigra), is a short-trunked forest tree with a spreading crown that can grow to 100 ft (30 m). It is native to Eastern North America, where it is found from New Brunswick south to Georgia and as far west as Kansas and Minnesota. Although chiefly valued for its decorative fine-grained wood, the tree's bark, root, leaves, and nuts all have medicinal properties. These qualities are similar to those of the closely related Juglans regia (better known as English walnut), the tree most commonly used by commercial walnut growers.
The main active ingredients of black walnut are tannins such as galloyglucose and ellagitannins, and juglone (5-hydroxy-alphanapthaquinone). Walnut shells are very rich in vitamin C, and betacarotene, B1,B2, and B6 are found in the leaves.
Herbalists use external applications of the plant for a variety of skin complaints including ringworm, jock itch, athlete's foot, psoriasis, blisters, eczema, scabbing pruritus, varicose ulcers, and even syphilis sores. The oil is a traditional hair tonic. Black walnut preparations have also been used for eye infections and irritations of the eyelid.
Internally, black walnut extracts are taken for ailments such as gout, rheumatism, glandular disturbances, worms, and parasites. It is also used to stimulate the appetite and as a laxative. Some authors consider it a blood purifier. There is evidence dating back to the 1960s showing that chemical components in the nut may help reduce blood pressure.
An April 2000 report in the Annals of Internal Medicine raised hope that walnuts might help reduce harmful LDL cholesterol. In a study conducted by a researcher at the Hospital Clinic Provincial in Barcelona, it was reported that substituting 8-11 walnuts a day for olive oil and other fatty foods in the cholesterol-lowering Mediterranean diet significantly improved the diet's effectiveness. In fact, the average reduction of LDL cholesterol in walnut dieters was twice that of participants using the traditional Mediterranean diet. However, the walnuts were added to a diet already known to be healthy, so the findings do not necessarily imply that addition of the nuts to a less nutritious diet would have a similar effect.
The ancient Doctrine of Signatures stated that hints to the healing properties of plants could be found in their physical appearance. In accordance with this belief, walnuts, with their convoluted surface, have long been thought useful in treating brain disorders. Discorides, the ancient Greek author of De materia medica which has
been the foremost textbook of pharmacology for 16 centuries, considered walnuts to have an excitatory effect on the head. This effect has been attributed to the plant's high levels of serotonin.
In East Asia, dried black walnut is used to treat cough, asthma, and bronchitis. In chronic bronchitis and asthma in older patients, it is given two or three times a day for as long as two months. This is said to improve appetite and sleep patterns. East Asian practitioners also employ the plant in kidney stone remedies to ease pain.
The plant has dental applications. Homeopaths use a tincture of black walnut leaves to treat cutting wisdom teeth. In Pakistan, walnut bark is used in toothpaste.
Black walnut extract can be bought at health food stores as a liquid or in capsules. Amateur herbalists can also prepare their own black walnut teas or salves. One traditional herbalist quoted in the 1989 book Herbal
The following formula for English walnut leaves is from the 1994 book Herbal Drugs and Phytopharmaceuticals: "Making the tea: 1.5 g [1.67 tsp] of the finely chopped [leaves are] put into cold water, heated to boiling, and after three to five minutes passed through a tea strainer, Internally as an adjuvant.. for skin conditions, a cupful of the tea is drunk one to three times a day. For dressings and lotions, a decoction of 5 g [5.6 tsp] drug in 200 ml [3.8 oz (US)] water is used."
Another source recommends an extract produced by boiling black walnut bark in water for 10 or 15 minutes.
According to folklore, drinking a mixture of walnut kernel ash and red wine prevents loss of hair, but also tints it blonde. Another traditional preparation was to gargle with juice from unripened green walnut husks mixed with honey.
Black walnut leaves should be collected, free of leafstalk, early in the summer. The nuts are considered mature four-and-a-half to five months after flowering, and are harvested in the fall. Commercial growers use trunk and limb shakers to remove walnuts when the green, fleshy shucks begin to split and the inner nut is a light tan color. They then use forced-air dryers to reduce the moisture content to 8%.
Directions and dosages should be carefully followed, as black walnut contains juglone, a powerful and toxic substance that prevents many plants from growing within the tree's root zone, extending as much as 80 ft (24 m) from a mature black walnut trunk. Juglone is especially strong in the roots, but is also found in the leaves, bark, and wood. Use of black walnut sawdust or wood chips as bedding material for horses has caused laminitis. In high doses, juglone is a kidney and liver toxin. Pollen from black walnut trees (usually shed in May) is a common cause of allergies in hypersensitive persons.
In their 1996 book Botanical Medicine: A European Professional Perspective, Dan Kenner and Yves Requena warn that black walnut should not be used against a cough involving fever.
Juglone can stain the skin yellow, brown, or black. This effect is so pronounced that black walnut oil is used to stain furniture and in artist's pigments.
Acknowledging the previous precautions, black walnut generally has no adverse side effects when properly administered in appropriate doses. However, users are advised to consult a health professional before using it.
Although interactions are unlikely, it is advisable to see a health professional before using black walnut extracts or capsules.
D'Amelio, Frank Sr. Botanicals: A Phytocosmetic Desk Reference. CRC Press, 1999.
Gruenewald, Joerg, Thomas Brendler, and Christof Jaenicke, eds. Physicians' Desk Reference for Herbal Medicines. Medical Economics Company, Inc., 1998.
Kenner, Dan and Yves Requena. Botanical Medicine: A European Professional Perspective. Paradigm Publications, 1996.
Zambon, Daniel, et al. "Substituting Walnuts for Monounsaturated Fat Improves the Serum Lipid Profile of Hypercholesterolemic Men and Women." Annals of Internal Medicine (April 2000) 132: 533-537.