Hazelnut

Other Names

Abellana nuxAlmindelig hasselAlunaAsian HazelAvellaAvellanaAvellana nux sylvestrisAvellanoAvellano De LambertAvellineBarcelona NutsBundukCobnutCollenCommon FilbertCommon HazelCorkscrew HazelCorylus americanaCorylus avellanaCorylus avellana L.Corylus avellana subsp. sylvestrisCorylus avellana var. sylvestrisCorylus heterophyllaCorylus imereticaCorylus laciniataCorylus maximaCorylus ponticaCorylus sylvestrisCorylus tubulosaCoudrierEuropäische HaselEuropean FilbertEuropean HazelEuropean HazelnutFandoqFilbernutFilbertFındıkFondukFoûntouciGiant FilbertHarry Lauder's Walking StickHaselnussHazelKalinKarua PontikaLeptokarionLombardy NutNocciolaNoisetteNux AvellanaNux PonticaPontic NutPontikón káryonPontus WalnutSiberian HazelnutSpanish Nut

Synopsis

Hazelnut (Corylus avellana L.): A Comprehensive Reference

1. Identity, Taxonomy, and Nomenclature

Corylus avellana is the most widely grown species of hazelnut, native to Europe, and is characterized by its matured ovary wall forming the shell and the edible nut meat representing the matured embryo. The hazel tree belongs to the birch family Betulaceae, Coryloideae subfamily, Corylus genus; so far 11–15 botanical species have been described, with Corylus avellana (European hazel) the species most extensively grown worldwide. The epithet avellana originates from Avella, an ancient town in Southern Italy traditionally known for the production of excellent hazels. The genus name Corylus comes from the Greek word korys, meaning helmet or hood.

Corylus avellana, commonly known as the European Hazelnut or Common Hazel, is a multi-stemmed deciduous shrub native to Europe and parts of western Asia, and is the main source of commercially grown hazelnuts. Other notable hazelnut species include the American hazelnut (Corylus americana), the beaked hazelnut (Corylus cornuta), and the California hazelnut (Corylus cornuta californica).

Corylus avellana occurs from Ireland and the British Isles south to Iberia, Italy, Greece, Turkey, and Cyprus, north to central Scandinavia, and east to the central Ural Mountains, the Caucasus, and northwestern Iran. Up to 400 cultivars of C. avellana have been named, including Barcelona, Butler, Ennis, Tonda di Giffoni, Tonda Gentile, and Tonda Romana, among others.

Common Names and Synonyms

The kernel of the hazel tree is known also as hazelnut, cobnut, or filbernut, and is edible raw or roasted.
Corylus maxima Mill. is recognized as a closely related large-fruited filbert species.
The American hazelnut is known as Corylus americana, or Corylus cornuta if beaked.

Common Forms and Preparations

The main products of C. avellana are kernels, a nutritious food with a high content of healthy lipids, used by the confectionery industry and consumed raw (with skin) or preferably roasted (without skin). Hazelnuts are used widely in the food industry, either as an ingredient in confectionery (chocolate, nougat, cookies, pralines, chopped nuts, nut spreads, and breakfast cereals) or in processed formulations such as praline paste and hazelnut oil. Hazelnut skin, hazelnut hard shell, and hazelnut green leafy cover, as well as hazelnut tree leaf, are byproducts of roasting, cracking, shelling/hulling, and harvesting processes, respectively. In commerce, hazelnuts are sold whole (raw or roasted, shelled or unshelled), as hazelnut oil, hazelnut paste/butter, hazelnut flour, and as standardized skin extracts.

2. Traditional and Historical Use

Prehistoric and Archaeological Evidence

Charred shells found in ancient middens from Scotland to the Pacific Northwest, dated at 9,000 years old, share a story of collective ancestors cultivating and consuming hazelnuts since the Stone Age. The European hazelnut was an important food source in the prehistoric diet during the Mesolithic period, which lasted from about 8,000 BC to 4,000 BC in northwestern Europe. Hazelnut remains were found all over Ireland in archaeological sites dating back approximately 10,000 years. In China, hazelnut shells dating back more than 5,000 years have been discovered, indicating their long history in Chinese culture.

Ancient Mediterranean Cultures

The ancient Greeks and Romans were known to have a fondness for hazelnuts and used them in a variety of dishes and desserts. They were also believed to have medicinal properties and were used to treat a variety of ailments. The Romans incorporated hazelnuts in their cuisine, particularly in desserts, and also used them to produce oil for cosmetic purposes. The ancient Greeks used hazelnuts in religious ceremonies and believed they possessed mystical properties.

Islamic and Medieval Scholarship

The great Turkish scholar Ibn-i Sina (Avicenna; 930–1037) mentions hazelnut as a medicine used in various diseases in his work al-Qanun fi'l-Tibb (The Canon of Medicine). The Middle Ages saw the cultivation of hazelnuts spread across Europe, with monasteries playing a pivotal role in their propagation; monks recognized the nut's health benefits and incorporated them into their daily diets and medicinal preparations.

Celtic and European Folklore

In Celtic traditions, the hazel tree was revered as a symbol of wisdom and knowledge, with its nuts believed to impart these qualities upon consumption. In folklore, hazelnuts were associated with wisdom, intelligence, and protection; they were believed to possess magical powers and were often used in rituals or charms to ward off evil spirits, and were also considered a symbol of fertility and abundance.

Native American Traditions

In pre-European North America, Native American tribal groups utilized native hazelnuts growing in the eastern woodlands, California, and Oregon. California indigenous groups used Corylus cornuta as roasted nuts for oils, in cakes, and for eating raw; nut milk was used medicinally for coughs and colds. Tribes such as the Cherokee and Dakota would roast, grind, and boil the nuts for various purposes. They used them in stews, soups, and bread. In addition to culinary uses, hazelnuts were used in traditional Native American medicine to treat colds, coughs, and gastrointestinal problems.

Traditional Chinese Medicine

In China, hazelnuts were utilized for medicinal purposes due to their believed ability to improve digestion and promote overall health. In traditional Chinese medicine, hazelnuts were often prescribed to nourish and balance the body's vital energies.

Traditional Preparations

Traditional preparations include pounding and soaking the hazelnuts to treat an upset stomach, and mixing powdered hazelnuts in honey to soothe a cough and other cold symptoms. In European herbal traditions, the bark was considered astringent and the leaves were used for their antioxidant, anti-inflammatory, and antimicrobial properties.

3. Key Constituents and Active Compounds

Macronutrient Composition

The main constituent of hazelnut fruits is fat, ranging from 56% to 61%, with a nutritional value of around 650 kcal per 100 g. Per 100 grams, hazelnuts contain approximately 628 kcal, approximately 15 g of protein, and a glycemic index of 15, according to USDA data. Hazelnuts are rich in protein and unsaturated fat, and also contain significant amounts of manganese, copper, vitamin E, thiamine, and magnesium.

Fatty Acids

The main fatty acids in hazelnut varieties are oleic acid (79.4%), linoleic acid (13.0%), and palmitic acid (5.4%). Hazelnuts may be associated with CVD prevention because of their fatty acid composition, mostly based on monounsaturated fatty acids (MUFA), which protect low-density lipoproteins (LDL) against oxidation. The high oleic acid content makes hazelnut oil one of the richest nut oil sources of monounsaturated fatty acids, comparable to olive oil.

Vitamin E (Tocopherols)

Turkish hazelnut is rich in the vitamin E active form (α-tocopherols), at 27.9 ± 11.3 mg/100 g. Among 11 types of nuts, hazelnut contains the highest concentration of vitamin E, folate, and biotin; 40 g of hazelnuts per day provides 100% of the daily requirement of vitamin E. In a study of 19 cultivars over three consecutive years, seven tocopherol and tocotrienol compounds were identified and quantified; all samples presented α-, β-, γ-, and δ-tocopherols and β-tocotrienol, with α-tocopherol as the major compound ranging from 105.9 to 226.8 mg/kg of hazelnut.

Phenolic Compounds

The prevalent phenolics accumulating in Corylus avellana kernels and their byproducts are catechin, gallic acid, sinapic acid, caffeic acid, p-coumaric acid, ferulic acid, their esters, and flavonoids. Hazelnuts contain 291–875 mg/100 g polyphenols. Among polyphenols present in hazelnuts there are phenolic acids, flavanols, flavon-3-ols, condensed tannins (procyanidins), and hydrolysable tannins; to a lesser extent there are also dihydrochalcones and flavonols. The total antioxidant capacity of hazelnut skin is a hundred times higher than that of the hazelnut kernel itself.

Minerals and Additional Micronutrients

Cobnuts (hazelnuts) are rich sources of minerals including manganese, potassium, calcium, copper, iron, magnesium, zinc, and selenium. Copper and manganese are essential co-factors for the antioxidant enzyme superoxide dismutase. Iron helps prevent microcytic anemia. Magnesium and phosphorus are vital components of bone metabolism. 100 g fresh nuts carry 113 µg of folate, about 28% of the recommended daily intake; folate is an essential B-complex vitamin that helps prevent megaloblastic anemia and neural tube defects in the newborn.

Phytosterols and L-Arginine

Hazelnuts contain oleic acid, polyunsaturated fatty acids, tocopherols, phytosterols, polyphenols, and L-arginine, all of which are known to exert antioxidant, anti-inflammatory, and cholesterol-lowering effects. Arginine, present at approximately 2.2 g per 100 g, promotes the synthesis of nitric oxide, which lowers blood pressure and relaxes blood vessels. 100 g of hazelnuts contains about 122 mg of phytosterols (plant sterols).

Hazelnut Skin: A Concentrated Bioactive Byproduct

Hazelnut skins — a major byproduct of roasting — contain even higher levels of polyphenols than the kernels themselves and are being explored for their nutraceutical potential. Concentration of total phenolic compounds in skins ranged between 51.9 and 203.1 mg gallic acid equivalent per gram of skin among varieties; total flavonoid content was almost 60% of the total phenolic compounds.

4. Mechanisms of Action

Antioxidant Defense

Vitamin E (α-tocopherol) is a lipid-soluble phenolic antioxidant; through its phenolic component, which donates a hydrogen atom to free radicals, it exerts antioxidant action, with roles in preventing atherosclerosis and diabetes. Polyphenols or secondary plant metabolites can act synergistically with phytochemicals, thus reducing oxidative stress and the risk of inflammatory diseases. In a human pilot trial, hazelnut consumption was associated with upregulation of antioxidant enzymes: after hazelnut consumption there was an upregulation of SOD1 (2−ΔΔCt = 2.42) and CAT (2−ΔΔCt = 2.41), two of the most important genes in the antioxidant pathway, due to their ability to catalyze the conversion of superoxide to oxygen and water.

LDL Protection and Anti-Atherogenic Actions

Hazelnuts may be associated with CVD prevention because of their MUFA-rich fatty acid composition, which protects LDL against oxidation. Moreover, hazelnuts are rich in various bioactive substances such as tocopherols, phytosterols, L-arginine, selenium, caffeic acid, dietary fibers, gallic acid, p-hydroxy benzoic acid, epicatechin, sinapic acid, and quercetin that could have anti-atherogenic effects by means of biological mechanisms acting on vascular function.

Anti-Inflammatory Gene Expression

Significant upregulation was detected for SOD1, CAT, MIF, PPARγ, VDR, MTHFR, and ACE after hazelnut consumption in a pilot human trial. According to emerging evidence, hazelnut consumption does not lead to weight gain, probably due to improvement of the body's antioxidant capacity by the upregulation of genes implied in oxidant reactions and inflammation.

Antiglycation Activity

Data suggest that phenolic compounds in hazelnut skin have an inhibitory effect on the BSA–advanced glycation end-product (AGE) model in vitro, and this effect is concentration-dependent. The putative role of hazelnut skin antioxidative properties in hindering AGE formation is also of interest. Enhanced production of AGEs plays an important role in the pathogenesis of diabetic complications, as well as in natural aging, renal failure, oxidative stress, and chronic inflammation.

Apoptotic and Anticancer Pathway Modulation

Hazelnut-derived compounds include modulation of mitochondrial apoptotic regulators (e.g., BAX/BCL-2), caspase activation, enhancement of antioxidant enzymes (e.g., SOD2, GSTP1), and rebalancing of gut–liver axis biomarkers such as bile acids. These mechanisms have been identified in in vitro and animal models; their clinical significance in humans is not yet established.

Hazel Leaf Phenolics

In cellular studies, hazel leaf phenolic fractions effectively inhibited the production of reactive oxygen species and malondialdehyde in TBHP-stimulated human umbilical vein endothelial cells by enhancing endogenous superoxide dismutase, and accordingly alleviated inflammatory cytokines (NO, IL-1β, TNF-α, and IL-6) in LPS-stimulated RAW264.7 cells, showing obvious antioxidant and anti-inflammatory capacity. These results are from in vitro studies only.

5. Scientific Evidence by Area of Use

5.1 Cardiovascular Health and Lipid Profile

Hazelnuts are rich in monounsaturated fatty acids and antioxidant bioactive substances; their consumption has been associated with a decreased risk of cardiovascular disease events. A systematic review and meta-analysis was performed to combine the results from several trials to estimate the pooled effect of hazelnuts on blood lipids and body weight outcomes. Nine studies representing 425 participants were included; the intervention diet lasted 28–84 days with a dosage of hazelnuts ranging from 29 to 69 g/day.

In a clinical study of 21 hypercholesterolemic volunteers in a double-control sandwich model intervention, participants underwent control diet I (4 weeks), a hazelnut-enriched diet (4 weeks; hazelnut contributing 18%–20% of the total daily energy intake), and control diet period II (4 weeks). This study demonstrated that substitution of hazelnuts for 18%–20% of the total daily energy intake showed multiple, potent antiatherogenic effects.

In a randomized controlled trial in a pediatric population, the effect of a dietary intervention with hazelnuts (15–30 g/day depending on patient weight) on serum lipid profile, anthropometric parameters, and fatty acid composition of erythrocyte phospholipids was investigated in an eight-week randomized, single-blind, controlled, three-arm, parallel-group study, enrolling 66 subjects with primary hyperlipidemia randomized to hazelnuts with skin, hazelnuts without skin, or dietary advice only. For the first time, a positive effect of hazelnut consumption on lipid profile and fatty acid composition of erythrocyte phospholipids in children with primary hyperlipidemia was documented.

Evidence strength: The cardiovascular lipid evidence is supported by a systematic review/meta-analysis and several clinical trials in both adults and children, and is considered moderate to good in quality for lipid-lowering effects. Study sizes are modest, and blinding of participants is inherently limited in dietary interventions.

5.2 Antioxidant and Oxidative Stress Biomarkers

A prospective pilot clinical trial on 24 healthy volunteers who consumed 40 g of hazelnuts daily as a snack for six weeks assessed anthropometric measurements, body composition analysis, and nutrigenomic analysis on 12 anti-inflammatory and antioxidant genes at baseline and after intervention. No significant changes were detected in body composition after hazelnut consumption. Significant upregulation of antioxidant enzymes SOD1 and CAT was confirmed after hazelnut consumption.

A separate study on short-term hazelnut consumption documented reduced DNA damage and oxidized LDL in children and adolescents with primary hyperlipidemia (published in Journal of Nutritional Biochemistry, 2018; PMID 29753234), representing a small but controlled clinical outcome. Hazelnut and its derivatives have demonstrated the ability to influence molecular targets relevant to cancer pathogenesis, including apoptosis regulation, oxidative stress mitigation, bile acid metabolism, and inflammatory signaling, as observed in vitro and in vivo.

Evidence strength: Human evidence for antioxidant gene modulation is currently limited to small pilot studies. In vitro and animal data are more extensive, but direct translation to clinical benefit in humans requires larger confirmatory trials.

5.3 Colorectal Cancer Prevention

A systematic review included a total of 11 studies after screening: 8 in vitro investigations, 2 in vivo animal experiments, and 1 epidemiological study. In vitro studies showed that hazelnut derivatives — including fermented hazelnuts and oil-based extracts — exert antiproliferative effects via BAX/BCL-2 modulation, increased caspase-3 activity, and oxidative stress reduction. In vivo studies confirmed improved lipid metabolism, modulation of bile acid composition (notably reduced lithocholic/deoxycholic acid ratio), and enhanced antioxidant defenses. FIBEROX®, a hazelnut skin extract enriched in dietary fiber, demonstrated promising effects on gut microbiota and bile acid detoxification.

Evidence strength: Currently preliminary. Evidence is almost entirely from in vitro and animal models. Only one epidemiological study was identified. No randomized controlled trials in human colorectal cancer prevention with hazelnut as the primary intervention were found in this review.

5.4 Antiglycation and Metabolic Effects

Data suggest that phenolic compounds in hazelnut skin have an inhibitory effect on the BSA–AGE model in vitro, and this effect is concentration-dependent. Because of the contribution of AGEs to the pathogenesis of several chronic diseases, foods enriched or supplements containing natural bioactive molecules able to inhibit their production could be a strategy for supporting therapeutic approaches with a positive effect on human health. No adequately powered human clinical trials specifically evaluating hazelnut supplementation on glycation outcomes were identified.

5.5 Body Weight

No significant changes were detected in body composition analysis after hazelnut consumption in one pilot study. According to emerging evidence, hazelnut consumption does not lead to weight gain, probably due to improvement of the body's antioxidant capacity. This is consistent with a broader nut literature showing that, despite high energy density, regular nut consumption is not strongly associated with weight gain, possibly due to satiety effects and incomplete fat absorption. The Bayesian meta-analysis of hazelnut trials also found no significant weight change across studies.

5.6 Antimicrobial Activity

Aqueous hazelnut extract presented antioxidant activity in a concentration-dependent manner. Hazelnut extracts revealed a high antimicrobial activity against Gram-positive bacteria, with a minimum inhibitory concentration (MIC) of 0.1 mg/mL, showing good bioactivity. Extracts of hazelnuts, due to their high content of polyphenols, have potent antioxidant properties and also antimicrobial activities. These findings are from in vitro studies; clinical antimicrobial applications have not been evaluated in controlled human trials.

5.7 Hazelnut Leaf and Bark: Traditional and Emerging Science

In hazel leaf, 35 phenolic substances of free, conjugated, and bound forms were identified including phenolic acids, flavonoids, and catechins; most were in free form. All fractions effectively inhibited reactive oxygen species and malondialdehyde production in TBHP-stimulated human umbilical vein endothelial cells and alleviated inflammatory cytokines in LPS-stimulated macrophages. These results are in vitro only and clinical evidence for leaf/bark preparations as therapeutic interventions is absent.

6. Body Systems Associated with Hazelnut

Cardiovascular system: Hazelnuts are rich in monounsaturated fatty acids and antioxidant bioactive substances; their consumption has been associated with a decreased risk of cardiovascular disease events.
Metabolic/endocrine system: Phytosterols contribute to cholesterol modulation; antiglycation compounds in the skin may be relevant to diabetic complications pathology, though human evidence is preliminary.
Gastrointestinal tract: FIBEROX®, a hazelnut skin extract enriched in dietary fiber, has demonstrated promising effects on gut microbiota and bile acid detoxification. Hazelnut skin's prebiotic potential is supported by early evidence of stimulation of beneficial Lactobacillus species.
Immune and oxidative stress: Combined with network pharmacology, the potential therapeutic effects and functional pathways of hazel leaf phenolics have been predicted, providing a value basis for exploring their treatment of diseases and developing health products.
Skin and topical use: Hazelnut oil has a nutty aroma, excellent astringent properties, and helps keep skin well protected from dryness. The oil has also been used in cooking and as a carrier or base oil in traditional medicines, massage therapy, aromatherapy, and in the pharmaceutical and cosmetic industry.
Reproductive/developmental health (folate): About 100 g of hazelnuts per day provides 60% of the folate (200 µg total daily folate) recommended for adults.

7. Dosage Forms and Dosages Reported in Studies

The following dosages are those reported in clinical studies only; they are not recommendations:

In the systematic review/meta-analysis of nine studies (425 participants), the intervention diet lasted 28–84 days with a dosage of hazelnuts ranging from 29 to 69 g/day.
A dietary intervention in children with primary hyperlipidemia used 15–30 g/day depending on patient weight, over eight weeks.
A study in hypercholesterolemic adults used a hazelnut-enriched diet contributing 18%–20% of total daily energy intake for four weeks.
A pilot clinical trial on 24 healthy volunteers used 40 g of hazelnuts daily as a snack for six weeks.
40 g of hazelnuts per day has been reported to provide 100% of the daily requirement of vitamin E.
Whole nuts (raw or roasted): The most common dietary form studied. Refining of hazelnut oil causes a significant decrease in bioactivity, measured as a decrease in tocopherols, phenolic compounds, and loss of carotenoids (lutein and zeaxanthin).

8. Safety Considerations and Allergenicity

Hazelnut Allergy: Allergen Proteins

For hazelnut, ten allergenic molecules have been identified and characterized: Cor a 1, Cor a 2, Cor a 8, Cor a 9, Cor a 10, Cor a 11, Cor a 12, Cor a 13, Cor a 14, and Cor a thaumatin-like protein (TLP). The readily available hazelnut component tests include cross-reactive protein Cor a 1 (PR-10) and Cor a 8 (lipid transfer protein, LTP), and the seed storage proteins Cor a 9 (11S globulin–legumin) and Cor a 14 (2S albumin).

Primary Hazelnut Allergy vs. Pollen-Food Syndrome

The clinical presentation varies from mild symptoms limited to the oropharynx (oral allergy syndrome, OAS) due to cross-reaction with homologues in pollen allergens, to more severe events caused by primary sensitization to highly stable molecules contained in hazelnuts.

Preschool and young school-age children generally present more severe systemic manifestations upon hazelnut ingestion, mainly due to sensitization to Cor a 9 (hazelnut legumin-like allergen) and unrelated to birch-related allergy. In contrast, adults living in birch-endemic areas generally report OAS on hazelnut intake resulting from the cross-reactivity between hazelnut allergen Cor a 1.04 and birch pollen allergen Bet v 1.

Birch Pollen Cross-Reactivity

There is over 97% cross-reactivity between birch pollen Bet v 1 and Cor a 1. In Central and Northern Europe, Cor a 1 IgE are detected in 60–90% of individuals with hazelnut sensitization. Among 161 hazelnut-sensitized patients from the Netherlands, 86% were sensitized to Cor a 1 and 87% were sensitized to Bet v 1. Patients mono-sensitized to Cor a 1 often tolerate roasted or heated hazelnuts, since Cor a 1 is a heat-labile protein.

Severe Reactions and Storage Proteins

Patients with specific IgE to seed storage proteins (Cor a 9 and Cor a 14) and LTP Cor a 8 are at higher risk of systemic reactions, while patients with specific IgE to the cross-reactive Cor a 1 usually only show local reactions. Diagnosis of hazelnut allergy is based on collection of clinical history, interpretation of sensitization test results (in vitro and in vivo), and execution of open or blinded oral food challenge (OFC).

Hazelnut Oil Safety

Refining of hazelnut oil causes a significant decrease in the bioactivity of the oil. Cold-pressed virgin hazelnut oil retains more bioactive compounds. No specific hepatotoxic, nephrotoxic, or serious adverse effects attributable to hazelnut kernel consumption at dietary quantities have been documented in the peer-reviewed literature reviewed here.

Caloric Density

Hazelnuts provide 622–628 kcal per 100 grams, making them a high-energy food. In the clinical trials reviewed, no significant weight gain was associated with consuming 29–69 g/day over periods up to 84 days, but the high caloric density warrants attention in overall energy-controlled dietary patterns.

Potential for Drug–Nutrient Interactions

Arginine in hazelnuts (approximately 2.2 g per 100 g) promotes synthesis of nitric oxide, which lowers blood pressure and relaxes blood vessels. Patients taking antihypertensive or nitrate medications may warrant consideration of substantial hazelnut consumption in the overall dietary context. No specific pharmacokinetic drug interaction studies specific to hazelnut supplementation were identified in the sources reviewed.

References

Health Conditions

Health conditions that Hazelnut may help support.

No conditions available.

Body Systems

Body systems that Hazelnut may help support.

No body systems available.