Medically reviewed on November 27, 2017
Scientific Name(s): Corylus avellana L. (common hazel); Corylus americana Walter (American hazel); Corylus colurna L. (Turkish hazel). Betulaceae (birch family)
Common Name(s): Hazelnut , dukkah (paste), filbert
Hazelnuts (raw, roasted, or ground into a paste) are used as a dietary source of protein and minerals. They are a source of vitamin E, unsaturated fatty acids, and linolenic acid. Hazelnut oil also is used in the cosmetic industry as well as in confectionery.
There are inadequate data to support dosing for therapeutic effect. Approximately 100 g of nuts delivers 15 mg of vitamin E.
Allergy to tree nuts or their products. Use caution in patients with known allergy to peanuts.
Information regarding safety and efficacy during pregnancy and lactation is lacking. Consumption of hazelnuts is generally recognized as safe when used as a food. No teratogenicity studies specific to hazelnut have been found.
None well documented.
Cross-reactivity with other tree nuts and co-allergy with peanuts have been described.
A review by the Cosmetic Ingredient Review Expert Panel concluded there are insufficient data to support the safety of hazelnut oil in cosmetic products. Carcinogenic aflatoxins are possible contaminants of hazelnuts.
The genus Corylus includes at least 11 species of hazel trees and hybrids also exist. 1 The trees grow from 3 to 8 m in height and were probably introduced into North America from Europe. Turkey is the leading producer of hazelnuts in the world. 2 The deciduous trees bear large (6 to 12 cm) rounded leaves with soft hairs on both surfaces and a doubly serrate margin. The tree flowers in early spring before the leaves develop, and the nuts hang in clusters of 1 to 5. A “husk” encloses 75% of the yellow-brown, spherical/oval nut, leaving a scar at the base of the hazelnut kernel. 1
In addition to consumption of the nuts as a source of protein, the leaves of the hazel tree have been used in folk medicine to relieve hemorrhoidal symptoms and varicose veins caused by purported vasoconstrictor properties. 3
The minerals of the nut include calcium, copper, iron, magnesium, manganese, phosphorus, selenium, and zinc; vitamins include alpha-tocopherol, ascorbic acid, folates, niacin, riboflavin, thiamin, and vitamin K as phylloquinone; fatty and amino acids include alanine, arginine, aspartic acid, glutamic acid, and leucine. 2 , 4 , 5
Tocopherol composition remains fairly consistent across geographic distribution and harvesting period. 6 The hazelnut is the best dietary nut source of alpha-tocopherol, containing 2 to 3 times more than olive oil. 7
The kernels contain about 60% seed oil, 2 , 7 which is derived by cold pressing. The oil contains saturated fatty acids (7%), mono- (78%) and polyunsaturated fatty acids (10%), and phytosterols (0.1%). 5 , 8 Composition of the oil varies with geographic origin 8 ; however, roasting the nuts prior to compressing appears to have little or no effect on oil composition. 2 , 9
Oleic, linoleic, linolenic, palmitoleic, and steric fatty acids are found in the oil. 2 , 7 , 10 Beta-sitosterol, campesterol, avenasterol, and clerosterol sterols have been identified, and their concentrations are dependent on geographic origin and harvesting period. 2 , 7 , 8
Uses and PharmacologyDietary uses
Hazelnuts are a dietary source of protein, unsaturated fats, minerals and micronutrients, phytochemicals, alpha-tocopherol, and fiber; they are considered a good source of tocopherol when used to meet the recommended daily allowance for vitamin E. 4 , 7 , 12Antioxidant
Antioxidant activity and radical scavenging properties of the kernel and green leaf/flower portions of the hazel tree have been demonstrated. 11 In doxorubicin-induced cataracts in rats, the administration of hazelnut was protective in lower-dose doxorubicin; hazelnut did not prevent cataracts at higher doses of doxorubicin. Because doxorubicin causes oxidative stress to cells, the anticataract effect is considered to be due to the antioxidant action of vitamin E and other elements found in the hazelnut (eg, copper, iron, selenium, zinc). 13Cardiprotective
Trials and epidemiological studies have found the consumption of nuts to be protective against cardiac morbidity and mortality. The Physicians' Health Study, a large prospective cohort study of United States physicians, associated dietary nut intake with a reduced risk of sudden cardiac death (47% lower risk for those who consumed nuts 2 or more times a week) but did not find it protective against nonfatal myocardial infarction. 14
In a small study, hazelnut supplementation of 1 g/kg body weight/day reduced low-density lipoprotein and total cholesterol and increased high-density lipoprotein and triglycerides. 12 Similarly, rabbits fed a high-cholesterol diet and concurrent hazelnut oil maintained their baseline lipid profiles. No effect of hazelnut oil on the lipid profile was found in the control rabbits fed a normal diet. Hazelnut oil was also protective against atherosclerotic plaque formation upon histological examination. 15Other
An antiprostaglandin/anti-inflammatory action has been described. 16
There are inadequate data to support dosing for therapeutic effect. One human trial used hazelnuts 1 g/kg body weight/day. 12 The recommended daily amount of 15 mg vitamin E would be contained in approximately 100 g of nuts. 5
Information regarding safety and efficacy during pregnancy and lactation is lacking.
Allergies to nuts are common in the United States (estimated 1%) 17 ; however, cross-reactivity to the proteins from tree nuts (hazelnut) among people with peanut (legume) allergies is considered low. Rather, a co-allergy is probably the cause of allergic reactions among these atopic individuals. Cross-reactivity between hazelnut and Brazil nut has been documented; similar proteins are found in the nuts of these botanically distinct trees. 18 , 19
Anaphylaxis, urticaria, vomiting, and wheezing have been reported in response to hazelnut consumption. Immunoglobulin E (mast cell) and T-cell (cytokine) responses are described. Because sensitization is required, the possibility of these responses occurring in utero or via breast milk has been postulated, but no high-quality studies exist to support this theory. 18 Oral desensitization to hazelnut may offer partial protection. 17
The use of antiulcer drugs is another possible method of sensitization to hazelnut. Hazelnut allergens are not resistant to gastric and pancreatic acid digestion, and the use of famotidine, omeprazole, ranitidine, and sucralfate in animal and human experiments displayed some evidence of this effect. 20
Placental transfer of fatty acids has been documented, but no teratogenicity studies specific to hazelnut have been found. 10
A review by the Cosmetic Ingredient Review Expert Panel concluded there are insufficient data to support safety of hazelnut oil in cosmetic products. 10
Aflatoxins are considered carcinogenic and are possible contaminants of hazelnuts. 10
Bibliography1. USDA, NRCS. 2006. The PLANTS Database ( http://plants.usda.gov , August 2006). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.
2. Crews C , Hough P , Godward J , et al. Study of the main constituents of some authentic hazelnut oils . J Agric Food Chem . 2005;53:4843-4852.
3. Amaral JS , Ferreres F , Andrade PB , et al. Phenolic profile of hazelnut ( Corylus avellana L.) leaves cultivars grown in Portugal . Nat Prod Res . 2005;19:157-163.
4. Alasalvar C , Shahidi F , Liyanapathirana CM , Ohshima T . Turkish Tombul hazelnut ( Corylus avellana L.). 1. Compositional characteristics . J Agric Food Chem . 2003;51:3790-3796.
5. US Department of Agriculture, Agricultural Research Service. 2005. USDA National Nutrient Database for Standard Reference, Release 18. http://www.ars.usda.gov/nutrientdata .
6. Amaral JS , Casal S , Alves MR , Seabra RM , Oliveira BP . Tocopherol and tocotrienol content of hazelnut cultivars grown in Portugal . J Agric Food Chem . 2006;54:1329-1336.
7. Alasalvar C , Shahidi F , Ohshima T , et al. Turkish Tombul hazelnut ( Corylus avellana L.). 2. Lipid characteristics and oxidative stability . J Agric Food Chem . 2003;51:3797-3805.
8. Amaral JS , Cunha SC , Santos A , Alves MR , Seabra RM , Oliveira BP . Influence of cultivar and environmental conditions on the triacylglycerol profile of hazelnut ( Corylus avellana L.) . J Agric Food Chem . 2006;54:449-456.
9. Amaral JS , Casal S , Seabra RM , Oliveira BP . Effects of roasting on hazelnut lipids . J Agric Food Chem . 2006;54:1315-1321.
10. Madhaven N . Final report on the safety assessment of Corylus Avellana (Hazel) Seed Oil, Corylus Americana (Hazel) Seed Oil, Corylus Avellana (Hazel) Seed Extract, Corylus Americana (Hazel) Seed Extract, Corylus Avellana (Hazel) leaf extract, Corylus Americana (Hazel) Leaf Extract, and Corylus Rostrata (Hazel) Leaf Extract . Int J Toxicol . 2001;20(suppl 1):15-20.
11. Alasalvar C , Karamac M , Amarowicz R , Shahidi F . Antioxidant and antiradical activities in extracts of hazelnut kernel ( Corylus avellana L.) and hazelnut green leafy cover . J Agric Food Chem . 2006;54:4826-4832.
12. Durak I , Koksal I , Kacmaz M , Buyukkocak S , Cimen BM , Ozturk HS . Hazelnut supplementation enhances plasma antioxidant potential and lowers plasma cholesterol levels . Clin Chim Acta . 1999;284:113-115.
13. Bayer A , Evereklioglu C , Demirkaya E , Altun S , Karslioglu Y , Sobaci G . Doxorubicin-induced cataract formation in rats and the inhibitory effects of hazelnut, a natural antioxidant: a histopathological study . Med Sci Monit . 2005;11:BR300-304.
14. Albert CM , Gaziano JM , Willett WC , Manson JE . Nut consumption and decreased risk of sudden cardiac death in the Physicians' Health Study . Arch Intern Med . 2002;162:1382-1387.
15. Balkan J , Hatipoglu A , Aykac-Toker G , Uysal M . Influence on hazelnut oil administration on peroxidation status of erythrocytes and apolipoprotein B 100-containing lipoproteins in rabbits fed on a high cholesterol diet . J Agric Food Chem . 2003;51:3905-3909.
16. Tunón H , Olavsdotter C , Bohlin L . Evaluation of anti-inflammatory activity of some Swedish medicinal plants. Inhibition of prostaglandin biosynthesis and PAF-induced exocytosis . J Ethnopharmacol . 1995;48:61-76.
17. Enrique E , Pineda F , Malek T , et al. Sublingual immunotherapy for hazelnut food allergy: a randomized, double-blind, placebo-controlled study with a standardized hazelnut extract . J Allergy Clin Immunol . 2005;116:1073-1079.
18. Sicherer SH , Simpson HA . Peanut and tree nut allergy . Curr Opin Pediat . 2000;12:567-573.
19. Asero R , Mistrello G , Roncarolo D , Amato S . Walnut-induced anaphylaxis with cross-reactivity to hazelnut and Brazil nut . J Allergy Clin Immunol . 2004;113:358-360.
20. Scholl I , Untersmayr E , Bakos N , et al. Antiulcer drugs promote oral sensitization and hypersensitivity to hazelnut allergens in BALB/c mice and humans . Am J Clin Nutr . 2005;81:154-160.
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