Medically reviewed on February 14, 2018.
Scientific Name(s): Juglans nigra . Family: Juglandaceae (walnuts)
Common Name(s): Black walnut , American walnut
Black walnut has many traditional uses; however, there are no human trials to support these effects. Black walnuts are a good dietary source of essential fatty acids.
No clinical trials are available to support dosage recommendations.
None well documented.
Avoid use. Documented adverse reactions (mutagenic properties).
None well documented.
Allergic reactions have occurred.
The quinones juglone and plumbagin found in black walnut are regarded as toxins.
There are approximately 15 species of Juglans walnuts. “Walnut” refers to several varieties, most commonly the English walnut ( Juglans regia ; see Walnut monograph) and the black walnut ( J. nigra ). Walnut trees have short trunks with round-topped crowns and can grow up to 45 m in height. The black walnut is native to the deciduous forests of the eastern United States (central Mississippi and Appalachian regions) and Canada. The wood is valued for its rich beauty and is used to make furniture, cabinets, and gun stocks. The fruit is an elongated drupe containing a 4-ribbed edible nut within a thick, hard, black shell that is smaller than the English walnut. 1 , 2
Walnuts have been found in prehistoric deposits dating from the Iron Age in Europe. In the Middle Ages, walnuts were thought to ward off witchcraft, the “evil eye,” and epileptic fits. Black walnut has been used in certain skin conditions, including eczema, pruritus, psoriasis, warts, and parasitic skin conditions. Treatment of eye irritations and styes are other uses for black walnut. 3 Extract of black walnut was used to dye the hair, skin, and clothing. 3 , 4 , 5 As a food, black walnut is commonly used in baked goods, candies, and frozen foods. 5 , 6 The traditional herbal medicine is extracted from the black, tarry, sticky part in the outermost hull.
Black walnuts contain juglone (5-hydroxy-1,4-naphthoquinone), alpha hydrojuglone and its glycoside beta-hydrojuglone, caffeic acid, plumbagin, hyperin, kaempferol, and tannin. Ellagic acid is also present. 3 , 7 , 8
Black walnuts contain 15 to 20 g of protein per 100 g. Trace minerals present include iron, zinc, sodium, phosphorus, and magnesium. 3 , 6 Black walnuts contain approximately 700 calories per 100 g, with fat (oil) content estimated to be about 60%. 6 The pesticide methyl 2-benzimidazolylcarbamate has been reported in black walnut fruit. 9
Uses and Pharmacology
No human clinical trials regarding black walnut and its many traditional uses have been recorded in the medical literature. Black walnut has been proposed as a candidate for chemotherapy because of the toxic nature of juglone and plumbagin, but studies to support this are lacking. 10 , 11Antioxidant
Black walnut is important for its nutritional value (see Chemistry). The nut is high in calories, a good source of protein, is rich in dietary fiber, and contains essential fatty acids. 3 , 5 , 6 See also the Walnut monograph.
No clinical trials are available to support dosage recommendations. Walnut leaves have been approved by the German Commission E for external application for excessive perspiration and skin inflammation. 14
None well documented.
Allergies to nuts are common in the United States (an estimated 1%), 17 with walnut and other tree nut allergy considered to be second only to peanuts (considered legumes) in anaphylactic reactions. Use care with topical preparations due to possible cytotoxic effects. 8 , 11
Little data exist. However, the naphthaquinone juglone, which is present in all species of the family Juglandaceae, is a known animal toxin. 18 , 19 , 20 , 21 Apoptosis and necrosis effects have been demonstrated in cancer cells with extracts of black walnut. Juglone and plumbagin, the yellow quinone pigments of black walnut, were shown to decrease cell viability and cell death. 8 , 11
Bibliography1. Juglans nigra . L. USDA, NRCS. 2007. The PLANTS Database ( http://plants.usda.gov , 28 October 2007). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.
2. Weber RW . Black walnut . Ann Allergy Asthma Immunol . 2003 ; 91 ( 3 ): A-6 .
3. D'Amelio FS . Botanicals: A Phytocosmetic Desk Reference . Boca Raton, FL: CRC Press; 1999 : 209 .
4. Hocking GM . A Dictionary of Natural Products . Medford, NJ: Plexus Publishing; 1997 : 409 .
5. Rosengarten F . The Book of Edible Nuts . New York, NY: Walker; 1984 : 239-262 .
6. Ensminger AH , et al. Foods & Nutrition Encyclopedia . 2nd ed. Boca Raton, FL: CRC Press; 1994 :2277-2278.
7. Bhargava UC , Westfall BA , Siehr DJ . Preliminary pharmacology of ellagic acid from Juglans nigra (black walnut) . J Pharm Sci . 1968 ; 57 ( 10 ): 1728-1732 .
8. Inbaraj JJ , Chignell CF . Cytotoxic action of juglone and plumbagin: a mechanistic study using HaCaT keratinocytes . Chem Res Toxicol . 2004 ; 17 ( 1 ): 55-62 .
9. Cline S , Felsot A , Wei L . Determination of methyl 2-benzimidazolylcarbamate in black walnut fruit . J Agric Food Chem . 1981 ; 29 ( 5 ): 1087-1088 .
10. Segura-Aguilar J , Jönsson K , Tidefelt U , Paul C . The cytotoxic effects of 5-OH-1,4-naphthoquinone and 5,8-diOH-1,4-naphthoquinone on doxorubicin-resistant human leukemia cells (HL-60) . Leuk Res . 1992 ; 16 ( 6-7 ): 631-637 .
11. Montoya J , Varela-Ramirez A , Estrada A , Martinez LE , Garza K , Aguilera RJ . A fluorescence-based rapid screening assay for cytotoxic compounds . Biochem Biophys Res Commun . 2004 ; 325 ( 4 ): 1517-1523 .
12. Halvorsen BL , Holte K , Myhrstad MC , et al. A systematic screening of total antioxidants in dietary plants . J Nutr . 2002 ; 132 ( 3 ): 461-471 .
13. Choi HR , Choi JS , Han YN , Bae SJ , Chung HY . Peroxynitrite scavenging activity of herb extracts . Phytother Res . 2002 ; 16 ( 4 ): 364-367 .
14. Blumenthal M , Goldberg A , Brinckmann J , eds. Herbal Medicine: Expanded Commission E Monographs . Newton, MA: Integrative Medicine Communications; 2000 .
15. Brinker FJ . Herb Contraindications and Drug Interactions . 2nd ed. Sandy, OR: Eclectic Medical Publications; 1998 .
16. McGuffin M , et al, ed. American Herbal Products Association's Botanical Safety Handbook . Boca Raton, FL: CRC Press; 1997 .
17. Sicherer SH , Sampson HA . Peanut and tree nut allergy . Curr Opin Pediatr . 2000 ; 12 ( 6 ): 567-573 .
18. True RG , Lowe JE . Induced juglone toxicosis in ponies and horses . Am J Vet Res . 1980 ; 41 ( 6 ): 944-945 .
19. Ralston SL , Rich VA . Black walnut toxicosis in horses . J Am Vet Med Assoc . 1983 ; 183 ( 10 ): 1095 .
20. Thomsen ME , Davis EG , Rush BR . Black walnut induced laminitis . Vet Hum Toxicol . 2000 ; 42 ( 1 ): 8-11 .
21. Galey FD , Beasley VR , Schaeffer D , Davis LE . Effect of an aqueous extract of black walnut ( Juglans nigra ) on isolated equine digital vessels . Am J Vet Res . 1990 ; 51 ( 1 ): 83-88 .
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