Skip to Content

Hazel

Scientific Name(s): Corylus americana Walter (American hazel)., Corylus avellana L. (common hazel)., Corylus colurna L. (Turkish hazel).
Common Name(s): Dukkah, Filbert, Hazelnut

Clinical Overview

Use

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.

Dosing

There are inadequate data to support dosing for therapeutic effect. Approximately 100 g of nuts delivers 15 mg of vitamin E.

Contraindications

Allergy to tree nuts or their products. Use caution in patients with known allergy to peanuts.

Pregnancy/Lactation

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.

Interactions

None well documented.

Adverse Reactions

Cross-reactivity with other tree nuts and co-allergy with peanuts have been described.

Toxicology

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.

Botany

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

History

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

Chemistry

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 oil2, 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 origin8; 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

Caffeoylquinic acid, caffeoyltartaric acid, coumaroyltartaric acid, myricetin, quercetin, and kaempferol phenols are found in hazel leaves, where 3, 11 tannins also have been identified.11

Uses and Pharmacology

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, 12

Dyslipidemia

Animal data

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.13

Clinical data

Results from a small stud revealed that hazelnut supplementation of 1 g/kg body weight/day showed reduced low-density lipoprotein and total cholesterol and increased high-density lipoprotein and triglycerides.12 Researchers have demonstrated improved lipid profiles (increased HDL and decreased LDL-C and total-C:HDL-C ratio) with hazelnut supplementation.14, 15

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.16

Assessment of data from 6,705 participants without baseline atrial fibrillation in the PREDIMED trial revealed a significant relevant reduction in risk of atrial fibrillation (38%) with the Mediterranean diet supplemented with extravirgin olive oil (50 g/day or more) but not with the Mediterranean diet supplemented with nuts (almonds, hazelnuts, walnuts).17

As a component of medical nutrition therapy for patients with type 2 diabetes, the American Diabetes Association Standards of Care (2014) recommend higher quality dietary fat intake, as an alternative to decreased fat intake, by replacing saturated and/or trans fats with mono- and poly-unsaturated fatty acids in the diet. This Mediterranean-style approach to eating may improve glycemic control and cardiovascular disease risk factors (moderate-quality evidence).18

Other uses

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).19

An antiprostaglandin/anti-inflammatory action has been described.20

Dosing

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

A clinical study has demonstrated acceptability of 30g hazelnuts daily, but not 60g daily.21, 22

Pregnancy / Lactation

Information regarding safety and efficacy during pregnancy and lactation is lacking.

Interactions

None documented.

Adverse Reactions

Allergies to nuts are common in the United States (estimated 1%)23; 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.24, 25

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.24 Oral desensitization to hazelnut may offer partial protection.23

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.26

Toxicology

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

References

1. 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;53:4843-4852.15941325
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;19:157-163.15715260
4. Alasalvar C, Shahidi F, Liyanapathirana CM, Ohshima T. Turkish Tombul hazelnut (Corylus avellana L.). 1. Compositional characteristics. J Agric Food Chem. 2003;51:3790-3796.12797745
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;54:1329-1336.16478256
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;51:3797-3805.12797746
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;54:449-456.16417303
9. Amaral JS, Casal S, Seabra RM, Oliveira BP. Effects of roasting on hazelnut lipids. J Agric Food Chem. 2006;54:1315-1321.16478254
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):15-20.11358108
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;54:4826-4832.16787035
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;284:113-115.10437650
13. 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;51:3905-3909.12797764
14. Tey SL, Delahunty C, Gray A, Chisholm A, Brown RC. Effects of regular consumption of different forms of almonds and hazelnuts on acceptance and blood lipids. Eur J Nutr. 2015;54(3):483-487.25433502
15. Tey SL, Brown RC, Chisholm AW, Delahunty CM, Gray AR, Williams SM. Effects of different forms of hazelnuts on blood lipids and α-tocopherol concentrations in mildly hypercholesterolemic individuals. Eur J Clin Nutr. 2011;65(1):117-124.20877394
16. 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;162:1382-1387.12076237
17. Martinez-Gonzalez MA, Toledo E, Aros F, et al. Extravirgin olive oil consumption reduces risk of atrial fibrillation-the PREDIMED (prevencion con dieta mediterranea) trial. Circulation. 2014;130:18-26.24787471
18. American Diabetes Association. Standards of medical care in diabetes--2014. Diabetes Care. 2014;37(suppl 1):S14-S80.24357209
19. 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:BR300-304.16049376
20. 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;48:61-76.8583796
21. Tey SL, Brown R, Chisholm A, Gray A, Williams S, Delahunty C. Current guidelines for nut consumption are achievable and sustainable: a hazelnut intervention. Br J Nutr. 2011;105(10):1503-1511.21272401
22. Tey SL, Gray AR, Chisholm AW, Delahunty CM, Brown RC. The dose of hazelnuts influences acceptance and diet quality but not inflammatory markers and body composition in overweight and obese individuals. J Nutr. 2013;143(8):1254-1262.23761651
23. 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;116:1073-1079.16275379
24. Sicherer SH, Simpson HA. Peanut and tree nut allergy. Curr Opin Pediat. 2000;12:567-573.11106277
25. Asero R, Mistrello G, Roncarolo D, Amato S. Walnut-induced anaphylaxis with cross-reactivity to hazelnut and Brazil nut. J Allergy Clin Immunol. 2004;113:358-360.14767457
26. 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;81:154-160.15640475

Disclaimer

This information relates to an herbal, vitamin, mineral or other dietary supplement. This product has not been reviewed by the FDA to determine whether it is safe or effective and is not subject to the quality standards and safety information collection standards that are applicable to most prescription drugs. This information should not be used to decide whether or not to take this product. This information does not endorse this product as safe, effective, or approved for treating any patient or health condition. This is only a brief summary of general information about this product. It does NOT include all information about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to this product. This information is not specific medical advice and does not replace information you receive from your health care provider. You should talk with your health care provider for complete information about the risks and benefits of using this product.

This product may adversely interact with certain health and medical conditions, other prescription and over-the-counter drugs, foods, or other dietary supplements. This product may be unsafe when used before surgery or other medical procedures. It is important to fully inform your doctor about the herbal, vitamins, mineral or any other supplements you are taking before any kind of surgery or medical procedure. With the exception of certain products that are generally recognized as safe in normal quantities, including use of folic acid and prenatal vitamins during pregnancy, this product has not been sufficiently studied to determine whether it is safe to use during pregnancy or nursing or by persons younger than 2 years of age.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

More about hazel

Hide