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
Medically reviewed by Drugs.com. Last updated on Oct 10, 2023.
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.
Scientific Family
- Betulaceae (birch)
Botany
The genus Corylus includes at least 11 species of hazel trees and hybrids also exist.USDA 2006 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.Crews 2005 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.USDA 2006
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.Amaral 2005
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.Alasalvar 2003, Crews 2005, USDA 2005
Tocopherol composition remains fairly consistent across geographic distribution and harvesting period.Amaral 2006 The hazelnut is the best dietary nut source of alpha-tocopherol, containing 2 to 3 times more than olive oil.Alasalvar 2003
The kernels contain about 60% seed oilAlasalvar 2003, Crews 2005 which is derived by cold pressing. The oil contains saturated fatty acids (7%), mono- (78%) and polyunsaturated fatty acids (10%), and phytosterols (0.1%).Amaral 2006, USDA 2005 Composition of the oil varies with geographic originAmaral 2006; however, roasting the nuts prior to compressing appears to have little or no effect on oil composition.Amaral 2006, Crews 2005
Oleic, linoleic, linolenic, palmitoleic, and steric fatty acids are found in the oil.Alasalvar 2003, Crews 2005, Madhaven 2001 Beta-sitosterol, campesterol, avenasterol, and clerosterol sterols have been identified, and their concentrations are dependent on geographic origin and harvesting period.Alasalvar 2003, Amaral 2006, Crews 2005
Caffeoylquinic acid, caffeoyltartaric acid, coumaroyltartaric acid, myricetin, quercetin, and kaempferol phenols are found in hazel leaves, where Alasalvar 2006, Amaral 2005 tannins also have been identified.Alasalvar 2006
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.(Alasalvar 2003, Alasalvar 2003, Durak 1999)
Cardiovascular risk
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.(Balkan 2003)
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.(Durak 1999) Researchers have demonstrated improved lipid profiles (increased HDL and decreased LDL-C and total-C:HDL-C ratio) with hazelnut supplementation.(Tey 2015, Tey 2011)
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.(Albert 2002)
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).(Martinez-Gonzalez 2014)
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).(ADA 2014)
Cataracts
Animal data
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).(Bayer 2005)
Cognitive effects
Animal data
Oral supplementation of hazelnuts (800 mg/kg/day) for 1 week in an Alzheimer rat model resulted in significant improvements in spatial working memory, memory impairment, and anxiety-like behavior. Increases in neuroinflammatory markers (ie, interleukin [IL}-1beta, cyclooxygenase [COX]-2, tumor necrosis factor [TNF]-alpha) induced in the untreated rat model were found to be reduced by at least 50% in animals supplemented with hazelnuts.(Bahaeddin 2017)
Obesity
In vitro data
Anti-obesity effects of a hazelnut extract (protein isolate) were identified in vitro with further purification of the peptide leading to a synthetic version that demonstrated significant inhibition of lipid accumulation and adipocyte differentiation.(Wang 2020)
Other uses
Antioxidant activity and radical scavenging properties of the kernel and green leaf/flower portions of the hazel tree have been demonstrated.(Alasalvar 2006)
An antiprostaglandin/anti-inflammatory action has been described.(Tunón 1995)
In vitro studies have demonstrated the ability of hazelnut oils to induce skeletal muscle cell differentiation and hypertrophy, which was not observed with olive oil.(Teruzzi 2018)
Dosing
There are inadequate data to support dosing for therapeutic effect. One human trial used hazelnuts 1 g/kg body weight/day.Durak 1999 The recommended daily amount of 15 mg vitamin E would be contained in approximately 100 g of nuts.USDA 2005
A clinical study has demonstrated acceptability of 30g hazelnuts daily, but not 60g daily.Tey 2011, Tey 2013
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%)Enrique 2005; 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.Asero 2004, Sicherer 2000
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.Sicherer 2000 Oral desensitization to hazelnut may offer partial protection.Enrique 2005
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.Scholl 2005
Toxicology
Placental transfer of fatty acids has been documented, but no teratogenicity studies specific to hazelnut have been found.Madhaven 2001
A review by the Cosmetic Ingredient Review Expert Panel concluded there are insufficient data to support safety of hazelnut oil in cosmetic products.Madhaven 2001
Aflatoxins are considered carcinogenic and are possible contaminants of hazelnuts.Madhaven 2001
References
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