European hazel

Other Names

AbeleiraAlunAvelãAveleiraAvellana nux sylvestrisAvellaneiroAvellanerAvellanoAvellano De LambertBarcelona NutsCobnutCollCollenCommon HazelCorylus avellanaCorylus avellana f. aureaCorylus avellana f. avellanaCorylus avellana f. contortaCorylus avellana f. fuscorubraCorylus avellana f. heterophyllaCorylus avellana f. pendulaCorylus avellana L.Corylus avellana subsp. sylvestrisCorylus avellana var. ponticaCorylus avellana var. sylvestrisCorylus imereticaCorylus ponticaCorylus sylvestrisCorylus tubulosaCoudrierEuropean FilbertEuropean HazelnutFilbertGemeine HaselGewöhnliche HaselGewone HazelaarGiant FilbertHarilik sarapuuHarry Lauder's Walking StickHaselaarHaselbuschHaselnussHaselstrauchHasselHazelHazelnutHurritzLazdaLeszczyna pospolitaLijeskaLíska obecnáNoccioloNocciolo comuneNoisetierNoisetier communNux AvellanaPaprastasis lazdynas

Synopsis

European Hazel (Corylus avellana L.): A Comprehensive Reference

1. Identity, Taxonomy, and Natural Source

Botanical Classification

Corylus avellana, the common hazel, is a species of flowering plant in the birch family Betulaceae. The hazel belongs to the birch family Betulaceae, Coryloideae subfamily, and the Corylus genus. So far 11–15 botanical species have been described; Corylus avellana — the European hazel — is the species most extensively grown worldwide. The epithet avellana originates from Avella, an ancient town in southern Italy traditionally known for its production of excellent hazels.

Common Names

The plant is commonly known under many names, including European hazel, European filbert, cobnut, hazelnut, and filbert. The ornamental contorted cultivar is additionally sometimes called Harry Lauder's Walking Stick or Corkscrew Hazel.

Geographic Origin and Distribution

Common hazel is native to Europe and western Asia, occurring 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. It is a wind-pollinated, deciduous, usually multi-stemmed, small tree often found in the understory of mixed deciduous forests.

Plant Morphology

European hazel is a deciduous, multi-stemmed shrub, though it can be pruned into a small tree; it forms a thicket of arching stems from the base, making it ideal for natural screens and edible hedges. It typically reaches a height of 10–20 feet (3–6 metres), but can occasionally grow up to 40–50 feet (12–15 metres) if left unpruned. Known for its distinctive, serrated leaves and catkin flowers, common hazel has been cultivated worldwide for both its edible nuts and wood.

Plant Parts Used

Most people encounter the plant through hazelnuts, but it has a much wider traditional footprint. The nuts are eaten raw, roasted, ground into spreads, or pressed into oil. The leaves have been used in folk herbalism, often as infusions, and the bark has appeared in traditional preparations for pain and vascular complaints. Industrial byproducts — including the shells (hard outer husk), the skin (pellicle surrounding the kernel), and the green leafy involucre (the husk surrounding immature nuts) — are increasingly studied for their phytochemical content.

Common Forms and Preparations

Whole kernel: consumed raw or roasted as a food or dietary supplement in nut form
Hazelnut oil: cold-pressed or expeller-pressed oil from the kernel, used in cosmetics, culinary, and traditional medicine applications
Leaf infusions and extracts: aqueous, hydroalcoholic, or standardized ethanolic extracts of dried leaves
Bark decoctions: traditional preparations involving boiling of bark in water
Standardized dietary supplement capsules: containing kernel or leaf extracts
Byproduct extracts: from shells, skins, and involucres — increasingly investigated as nutraceutical ingredients

2. Traditional and Historical Use

Prehistoric and Ancient Use

Hazelnuts have been an essential part of human diets since the Stone Age. Human beings have made use of the species since the Mesolithic and Neolithic eras: evidence has been unearthed at archaeological sites in Sweden, Denmark, and Germany. Chinese manuscripts mentioned hazelnuts 5,000 years ago when they were used both as food and for their therapeutic properties.

Classical Antiquity

Historical records from ancient Greece and Rome indicate that hazelnuts were used not only as food but also for their purported health benefits, including support for cardiovascular health and as a general tonic. The ancient Roman author and naturalist Pliny the Elder refers to a nux Pontica whose origins were supposed to have been in Turkey, south of the Black Sea.

European Folk and Herbal Medicine

In traditional European and regional folk practice, hazel leaves and bark were used as mild astringent and vascular-support herbs, while the nuts were valued as an energy-rich food that also supplied healthy fats, vitamin E, folate, and protective plant compounds. For centuries, the leaves, bark, and nuts of the hazel tree were valued in folk remedies. Ancient herbalists often prepared infusions or decoctions from the leaves and bark to support circulatory health, reduce inflammation, and address venous insufficiency.

Seventeenth-century herbalist William Coles used many parts of the hazel, including the husks, shells, and skins of the nuts — each taken in red wine for their astringent properties — while hazel catkins and the inner rind of small branches were administered to treat strangury, a term referring to the inability to produce urine. In traditional Swedish medicine, the leaf and bark were used to treat pain.

Traditional medicine uses the leaves in the form of aqueous or hydroalcoholic extract for treating small lesions, and the bark in cases of intermittent nonspecific fever. In European folk medicine, hazelnut oil was a well-known emollient for babies' cradle caps or to soften chapped hands in winter. The oil-pressed nuts also appeared in salves for rheumatic joints, often mixed with camphor and rosemary.

Galenic preparations of hazel leaves have also been used to relieve ulcers and oropharyngeal infections, with reported mild anti-dysentery, anti-fungal, and scarring properties.

Hazel has been an important component of the hedgerows used as traditional field boundaries in lowland England, and the wood was traditionally grown as coppice, with poles used for wattle-and-daub building.

Judging by the absence of hazel from most herbals after the mid-18th century, hazel seems to have lost popularity in medicine, with attention turning more to the American witch hazel.

3. Key Constituents and Active Compounds

Lipid Fraction (Kernel)

The lipid portion is the main component of the hazelnut kernel and may constitute more than 60% of the hazelnuts' dry weight; the monounsaturated fatty acids (mainly oleic acid, 18:1n-9) make up the largest portion (mean value 80.85%), followed by polyunsaturated fatty acids (10.70%). The main fatty acids in hazelnut varieties are oleic (79.4%), linoleic (13.0%), and palmitic acid (5.4%). Saturated fatty acids are the minor components and account for only approximately 8.43% of total fatty acids.

Hazelnuts are also rich in protein and unsaturated fat; they also contain significant amounts of manganese, copper, vitamin E, thiamine, and magnesium. The average niacin, vitamin B1, vitamin B2, vitamin B6, ascorbic acid, folic acid, retinol, and total tocopherol contents of hazelnut kernels were 1.45 mg/100 g, 0.28 mg/100 g, 0.05 mg/100 g, 0.5 mg/100 g, 2.45 mg/100 g, 0.043 mg/100 g, 3.25 mg/100 g, and 26.9 mg/100 g, respectively.

Protein and Amino Acids

The protein content of the hazelnut kernel ranges between 10% and 24%. Essential amino acids, primarily arginine (2,003 mg/100 g) and leucine (1,150 mg/100 g), and non-essential amino acids, primarily glutamic acid (2,714 mg/100 g) and aspartic acid (1,493 mg/100 g), have been determined in hazelnut varieties.

Phenolic Compounds and Antioxidants

European hazelnut contains many important phytochemicals, including phenolic acids, flavonoids, tannins, proanthocyanidins, diarylheptanoids, lignans, taxanes, and volatile compounds. Leaves specifically contain myricetin, caffeic acid, chlorogenic acid, quercetin, betulin, volatile oil, sugars, and minerals. A total of 18 phenolic compounds have been quantitatively determined across 57 hazelnut cultivars.

A byproduct of industrial hazelnut processing — roasted hazelnut husk — is rich in phenolic compounds, especially proanthocyanidins A and B. Condensed tannins or proanthocyanidins have been associated with positive effects on neurogenesis, cognitive improvement, and prevention of neuron death in neurodegenerative diseases such as Alzheimer's disease in preclinical models.

Hazelnut also contains antioxidant phenolics such as caffeic acid, along with minerals including manganese, copper, chromium, iron, phosphorus, calcium, and zinc, and other compounds including choline, betaine, and dietary fibre.

Diarylheptanoids

Polar extracts of the shells, leaves, and green leafy covers of C. avellana contain numerous metabolites belonging to the diarylheptanoid class, along with flavonoids, neolignans, and phenylpropanoids, which have been investigated for cytotoxic activities against different human cancer cell lines.

Taxanes

Hazel (Corylus avellana), already cultivated for its nutritional value, has attracted extensive attention due to the discovery of taxol and related taxanes within the plant species, prompting considerable interest to explore biotechnological production of these compounds using in vitro cultures. Among the identified compounds are paclitaxel, 10-deacetylbaccatin III, baccatin III, paclitaxel C, and 7-epipaclitaxel. Paclitaxel (Taxol™) is known for its antimitotic effect in the G2-M phase of the cell cycle, leading to important antitumor activity. A review of the literature suggests that C. avellana may act as a commercial and alternative source for taxol production.

Phytosterols

Hazelnut kernels and byproducts contain phytosterols, including β-sitosterol. Qualitative and quantitative analyses using LC-MS and LC-MS/MS in hazelnut involucre extracts have revealed important amounts of individual polyphenols and phytosterols — molecules with antioxidant potential.

Compounds from Kernel with Novel Bioactivities

Compounds isolated from hazelnut kernels — including newly characterized hazelnutins A–F — inhibited COX-2 expression with inhibition rates ranging from 36.10 to 64.08%; some compounds inhibited the proliferation of Candida albicans; and compound 11 exhibited potent antioxidant activity against ABTS and DPPH with IC50 values of 11.22 and 13.21 μmol/L, respectively.

4. Mechanisms of Action

Cardiovascular: Lipid Modulation

Hazelnuts may be associated with cardiovascular disease 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 is thought to substitute dietary saturated fat and thereby improve the LDL-to-HDL ratio.

Anti-inflammatory and Antioxidant Mechanisms

Hazelnuts are considered an excellent anti-inflammatory and hypolipidemic food, being the second richest source of monounsaturated fatty acids among nuts and because they are rich in vitamins, minerals, and phenolic compounds. The flavonoids and polyphenols in hazel — including quercetin, myricetin, chlorogenic acid, and caffeic acid — are understood to act as free radical scavengers. Compounds isolated from hazelnut kernels inhibit COX-2 expression, which is a key pro-inflammatory enzyme.

Antimitotic (Taxane) Mechanism

Among hazelnut taxanes, paclitaxel is known for its antimitotic effect in the G2-M phase of the cell cycle, leading to important antitumor activity. Such chemotherapeutic agents have demonstrated the ability to inhibit metaphase-anaphase transition in a human lung cancer cell line (SK-Mes-1). It must be noted that concentrations of taxanes in hazel plant material are very low, and no clinical applications of hazel as a taxane source in humans have been established.

Immunomodulatory Mechanism

A study employing healthy human donors' monocyte-derived macrophages (MDMs) in primary culture treated with a whole extract of Corylus avellana 'Tonda Gentile Romana' (kernel and skin) assessed whether it could strengthen the innate immune response against an intracellular bacterial infection with Staphylococcus aureus. The study aimed to clarify whether the extract could enhance the bactericidal response of human macrophages, suggesting a possible immunomodulatory function.

5. Scientific Evidence by Area of Use

5.1 Cardiovascular Health and Lipid Profile

This is the best-studied area for Corylus avellana as a dietary supplement, with multiple human intervention trials and a systematic review and meta-analysis.

Systematic review and meta-analysis: A systematic review and Bayesian meta-analysis combined results from multiple trials to estimate the pooled effect of hazelnuts on blood lipids and body weight outcomes. Nine studies representing 425 participants were included; intervention diets lasted 28–84 days with hazelnut doses ranging from 29 to 69 g/day. Out of nine studies, three randomized studies were meta-analyzed, showing a significant reduction in LDL cholesterol (pooled MDΔ = −0.150 mmol/L; 95% highest posterior density interval = −0.308 to −0.003) in favor of hazelnut consumption. A hazelnut-enriched diet decreased LDL cholesterol significantly and showed a trend toward reduction of total cholesterol, without decreasing HDL cholesterol, while triglycerides and BMI remained substantially unchanged.

Hypercholesterolemic adults (crossover study): Fifteen hypercholesterolemic men aged 48 ± 8 years were recruited in a well-controlled two-period study design totalling 8 weeks. In the first period, subjects consumed a control diet (low-fat, low-cholesterol, high-carbohydrate); in the second period, the control diet was supplemented with MUFA-rich hazelnut (40 g/day), providing 11.6% of total energy content.

Hazelnut-enriched diet and endothelial function: Consumption of a hazelnut-enriched diet significantly improved flow-mediated dilation (FMD) by 56.6%, total cholesterol (−7.8%), triacylglycerol (−7.3%), LDL-cholesterol (−6.17%), and HDL-cholesterol (+6.07%) compared with a control diet. Additionally, oxidized-LDL, high-sensitivity C-reactive protein (hs-CRP), and soluble vascular cell adhesion molecule-1 (sVCAM-1) levels were significantly lower in the hazelnut-enriched diet group compared with control diets. Hazelnut-enriched diets may exert an antiatherogenic effect by improving endothelial function, preventing LDL oxidation, and reducing inflammatory markers, in addition to lipid-lowering effects; however, these beneficial effects appeared to be reversible after 4 weeks on a hazelnut-free diet.

Children with hyperlipidemia (RCT): A dietary intervention with roasted Italian hazelnuts (Corylus avellana L.) consumed daily for 8 weeks investigated effects on serum lipid profiles and fatty acid composition of red blood cell phospholipids in children and adolescents with primary hyperlipidemia. Two intervention arms were considered — hazelnut with skin and hazelnut without skin — with a third group receiving only dietary advice as control. A total of 66 children and adolescents with primary hyperlipidemia (mean age 11.6 ± 2.6 years) were enrolled.

Evidence strength: These data show a potentially favorable effect on cardiovascular disease prevention and suggest the need for further research with long-term intervention studies and large study groups in order to confirm and subsequently promote the consumption of hazelnuts to benefit physiological cholesterol serum patterns. The overall cardiovascular evidence is moderate in strength for LDL reduction; most studies are short-term (4–12 weeks) and conducted in specific populations. Long-term cardiovascular event data are not yet available for hazelnut specifically.

5.2 Oxidative Stress and Inflammation

Prospective pilot trial: A prospective pilot clinical trial on 24 healthy volunteers who consumed daily, as a snack, 40 g of hazelnuts (261.99 kcal/1,096.17 kJ) for six weeks evaluated anthropometric measurements, body composition, and nutrigenomic analysis on 12 anti-inflammatory and antioxidant genes at baseline and after the intervention. The study assessed gene expression changes rather than clinical endpoints. Inflammation is associated with obesity and plays a pivotal role in the onset and progression of chronic diseases; hazelnuts are considered an excellent anti-inflammatory and hypolipidemic food, being the second richest source of MUFAs among nuts, and because they are rich in vitamins, minerals, and phenolic compounds.

Evidence strength: Evidence for anti-inflammatory effects from whole hazelnut consumption in humans is preliminary. The available human data consists of a small pilot trial; results from larger controlled trials are needed. In vitro evidence for anti-inflammatory activity of hazel leaf and shell extracts is more extensive but not yet translated into clinical trials.

5.3 Antioxidant Activity

An overview of biological activity across hazelnut kernel and byproducts covers mainly antioxidant, antiproliferative, and antimicrobial effects, along with less common biological effects, contributing to highlighting C. avellana as a source of bioactive phytochemicals with potential to exert beneficial effects on human health. Aqueous hazelnut extract has demonstrated antioxidant activity in a concentration-dependent manner; hazelnut extracts have also revealed high antimicrobial activity against Gram-positive bacteria (MIC 0.1 mg/mL).

Evidence strength: Antioxidant activity evidence is strong in vitro but lacks robust human clinical data. Plasma antioxidant capacity improvements have been reported in some nut consumption studies, but hazel-specific human data remain limited.

5.4 Anticancer / Antiproliferative Activity (Taxane-Related)

The discovery of taxol and related taxanes in C. avellana prompted extensive interest in exploring biotechnological production of these compounds using in vitro cultures. Cell culture extracts of hazelnut were reported to be more effective than pure Taxol against certain human cancer cell lines. Polar extracts of shells, leaves, and green leafy covers of the Italian C. avellana cultivar 'Tonda di Giffoni' — yielding numerous metabolites including diarylheptanoids, flavonoids, neolignans, and phenylpropanoids — were investigated for cytotoxic activities against human lung adenocarcinoma (A549), human epithelioid cervix carcinoma (HeLa), human skin fibroblasts (HaCaT), human B lymphoma (DeFew), and human osteosarcomas (U2Os and SAOs) cell lines. Neither single phenolics (in concentrations between 10 and 100 μM) nor methanol extracts (at 500 μg/mL and 250 μg/mL) of hazelnut byproducts caused a significant cytotoxic effect in those assays.

Evidence strength: Evidence is entirely preclinical (in vitro and cell-line studies). There are no human clinical trials using hazel-derived taxanes or other hazel extracts as cancer therapeutics. The amounts of taxanes found in hazel plant material are extremely small, and the research interest is primarily in biotechnological production of paclitaxel rather than direct consumption of the plant for anticancer effects.

5.5 Antimicrobial Activity

Antioxidant potential of hazelnut cultivars has been assessed using the reducing power assay, DPPH radical scavenging, and beta-carotene linoleate model system; antimicrobial capacity has also been tested against Gram-positive bacteria (Bacillus cereus, B. subtilis, Staphylococcus aureus), Gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae), and fungi (Candida albicans, Cryptococcus neoformans). Hazelnut extracts revealed high antimicrobial activity against Gram-positive bacteria (MIC 0.1 mg/mL).

Evidence strength: All antimicrobial data are in vitro. No clinical trials have evaluated hazel preparations for treatment of infectious conditions in humans. This area remains preclinical.

5.6 Neurological Health

Databases including PubMed and ScienceDirect have been searched for research on hazelnut (Corylus avellana) and its major chemical contents (lipids, proteins, vitamins) related to Alzheimer's disease and possible mechanisms of action, including keywords such as dementia, memory, cognition, neurogenesis, and nootropic. In animal model studies, hazelnut varieties were protective against β-amyloid-induced neurochemical changes and high-fat diet-induced alteration of metabolic indices. Condensed tannins or proanthocyanidins in hazelnut have been associated in preclinical research with positive effects on neurogenesis, cognitive improvement, and prevention of neuron death in neurodegenerative diseases such as Alzheimer's disease.

Evidence strength: Evidence is preclinical (in vitro and animal models). No human clinical trials have evaluated hazel-specific preparations for neurological or cognitive outcomes. This is an area of early investigational interest only.

6. Body Systems and Health Areas of Association

Cardiovascular system: LDL cholesterol reduction, improvement of endothelial function (FMD), reduction of oxidized-LDL and inflammatory markers (hs-CRP, sVCAM-1) — supported by multiple clinical trials.
Antioxidant defense: free radical scavenging via phenolics, tocopherols, and monounsaturated fat protection of LDL; supported by in vitro studies and some clinical markers.
Inflammatory regulation: COX-2 inhibition in vitro; gene expression modulation in a pilot human study; primarily preclinical evidence.
Integumentary system (skin): traditional use of hazelnut oil as an emollient; in vitro evidence for moisturizing and barrier-protective properties from oleic acid content.
Immune system: preclinical evidence that hazelnut kernel extracts may enhance macrophage bactericidal function.
Nervous system / cognition: preclinical animal and in vitro data linking proanthocyanidins and other phenolics to neuroprotection; no human trial data.
Antimicrobial defense: in vitro data only; no clinical application established.
Oncological: presence of taxanes in plant material is scientifically notable; preclinical cell-line data only; no clinical applications established using hazel as a source.

7. Dosage Forms and Dosages Reported in Studies

The following dosages are reported from human studies and should not be extrapolated as recommendations:

Intervention diets in the systematic meta-analysis lasted 28–84 days, with a dosage of hazelnuts ranging from 29 to 69 g/day.
In one crossover study in hypercholesterolemic men, the control diet was supplemented with 40 g/day of MUFA-rich hazelnut, which provided 11.6% of total energy content.
In the pilot clinical trial on healthy volunteers, 40 g of hazelnuts (261.99 kcal/1,096.17 kJ) were consumed daily as a snack for six weeks.
In the pediatric RCT, roasted Italian hazelnuts were consumed daily for 8 weeks; specific per-day quantities were not disclosed in the available excerpt.

Hazel leaf tea and extracts have traditional uses, but they do not yet have a well-standardized medicinal dose. No standardized clinical dosing regimens for leaf, bark, or non-kernel extracts of Corylus avellana have been established in peer-reviewed human studies.

8. Safety, Adverse Effects, and Interactions

Allergy: A Major Safety Consideration

Hazelnuts (Corylus avellana) are among the common tree nuts that lead to allergic reactions. Hazelnut allergy varies from rather mild oral allergy symptoms to potentially life-threatening anaphylaxis, and exhibits geographic and age-related variations. It is the most common tree nut allergy in Europe.

Upon ingestion, hazelnut may induce allergic reactions in two ways: as primary immunoglobulin E (IgE)-mediated food allergy, or as oral allergy syndrome (OAS) associated with pollen allergy.

In children, sensitization predominantly occurs to hazelnut storage proteins Cor a 9 and Cor a 11, unrelated to birch pollen allergy, and is generally associated with a more severe clinical outcome on consumption of raw and processed hazelnut. In contrast, adults predominantly present with an oral allergy syndrome due to extensive cross-reactivity between the labile Cor a 1.04 and Bet v 1, the major allergen from birch (Betula verrucosa) pollen.

The major hazelnut allergen was found to have a molecular mass of about 17–18 kDa and to share IgE epitopes with Bet v 1, the major birch pollen allergen; this allergen was recognized by IgE in 93% of hazelnut-allergic patients studied.

Hazelnut allergy is common, often persistent, and associated with the risk of severe systemic reactions and anaphylaxis. Distinguishing between primary hazelnut allergy and cross-reactions with pollens, especially birch, is crucial for accurate diagnosis and effective treatment.

Hazelnut allergy is considered birch pollen-related in north-western Europe, while in southern Europe it is considered a pollen-unrelated allergy. Hazelnut allergy may also occur in association with other tree nut allergies, including peanut, walnut, pecan, almond, cashew, pistachio, macadamia, and Brazil nut.

In the absence of a cure, avoidance remains the key measure of effective management, particularly in patients presenting with a severe form of hazelnut allergy.

Mycotoxin Contamination

Carcinogenic aflatoxins are possible contaminants of hazelnuts. Aflatoxin contamination is a recognized food safety issue for tree nuts, including hazelnut, that can occur under conditions of improper storage.

Adulteration

Hazelnut paste may be adulterated with vegetable oils. This is a commercially documented concern particularly affecting processed hazelnut products.

Caloric Density

The main constituent of hazelnut fruits is fat, ranging from 56% to 61%, with a nutritional value of approximately 650 kcal per 100 g of fruits. Despite hazelnut supplementation not significantly increasing BMI in short intervention studies, the high caloric density of hazelnuts is a practical consideration when they are used as a supplement in substantial quantities.

Leaf and Bark Safety

The hazelnut kernel has stronger human evidence, especially for cardiometabolic support within a balanced diet, while the leaf shows promising antioxidant and anti-inflammatory activity in laboratory research but still lacks strong clinical confirmation. Safety data for extended use of leaf and bark preparations in humans are not well established in the peer-reviewed literature, and standardized preparation or dosing protocols for these forms are not available from clinical trials.

References

Health Conditions

Health conditions that European hazel may help support.

No conditions available.

Body Systems

Body systems that European hazel may help support.

No body systems available.