Nettles, Nettle (Urtica dioica L.)

Nettle is a perennial herbaceous species with a rhizomatous growth habit, belonging to the Urticaceae family. It is widespread across much of Europe, temperate Asia and other temperate regions worldwide. It prefers cool, nutrient-rich environments, such as woodland edges, fallows, hedgerows and disturbed or semi-anthropised areas. The plant has an erect, often quadrangular stem, sparsely to moderately branched, and can form dense stands thanks to its creeping rhizomes. The leaves are opposite, ovate to lanceolate, with a serrated margin and a surface covered with numerous stinging hairs, also present on the stem, containing mixtures of irritant substances. Inflorescences are pendulous or erect catkin-like clusters, bearing small greenish flowers, with male and female flowers typically found on separate plants (dioecious species). The fruits are small achenes each containing a single seed.

From an ecological and agronomic perspective, nettle is a hardy and competitive species, indicative of nitrogen-rich soils with a good supply of organic matter. It thrives in moist or fresh sites, on medium to heavy soils, often with a tendency to be clayey, provided they are not subject to prolonged waterlogging. It tolerates partial shade but shows more vigorous growth in semi-shaded to full-sun exposures when water availability is adequate. Its ability to propagate via rhizomes makes nettle potentially invasive under favourable conditions. Biomass production, active constituent content and overall quality are influenced by harvest time, soil fertility, moisture availability and seasonal climatic conditions.

From a compositional standpoint, nettle leaves contain a high proportion of water, a relatively significant protein fraction compared with many other wild herbaceous species, fibre (especially in more mature leaves), chlorophyll and various phenolic compounds and flavonoids. They also include organic acids, small amounts of carotenoids and a noteworthy mineral component, with calcium, magnesium, potassium and iron occurring at appreciable levels, which vary according to developmental stage, plant part and pedoclimatic conditions. The overall composition profile is strongly affected by tissue age, soil characteristics, nutrient availability and drying or processing methods.

From a food and technological perspective, young nettle leaves are used, after appropriate processing (washing and cooking or blanching), as an ingredient in culinary preparations such as soups, fillings, sauces and vegetable-based dishes. Part of the harvested material is destined for the production of herbal teas and infusions obtained from dried plant material, sometimes in combination with other species. Nettle extracts are used in herbal applications and certain technical formulations. Stems, which are rich in bast fibres, have traditionally been used, albeit on a limited scale, to obtain textile fibres or for small-scale technical uses.

The quality assessment of nettle material intended for processing (particularly leaves and dried herb) considers uniform particle size, cleanliness (absence of coarse, woody stems, soil or foreign matter), colour (leaf material as uniformly green as possible), a characteristic, non-off-odour, and the absence of visible signs of mould, fermentation or degradation. Key factors include the harvest stage and method, drying conditions, any subsequent fragmentation and storage practices, all of which are crucial to preserving the main technological and organoleptic properties of the raw material.

Botanical classification (APG IV system)

• Common name: Nettle

• Botanical name: Urtica dioica L.

• Kingdom: Plantae

• Clade: Angiosperms → Eudicots → Rosids

• Order: Rosales

• Family: Urticaceae

• Genus: Urtica

• Species: Urtica dioica L.

Indicative nutritional values per 100 g (fresh edible leaves)

Values refer to fresh leaves. They may vary depending on habitat, season, harvest stage and analytical method.

Fresh nettle stands out for its notable mineral density (especially calcium, potassium, magnesium and phosphorus), meaningful vitamin C content, carotenoids (precursor of vitamin A), and a protein fraction higher than most leafy vegetables.

Mini-glossary of acronyms

• SFA = Saturated fatty acids. When they prevail over unsaturated fats in the diet, they are considered less favourable for cardiovascular balance.

• MUFA = Monounsaturated fatty acids. Generally regarded as more favourable than saturated fats when replacing them.

• PUFA = Polyunsaturated fatty acids. Include omega-6 and omega-3, essential in small amounts and involved in cell membrane structure and inflammatory processes.

Plant Characteristics

• Height: Can grow between 50 cm and 1.5 meters.
• Stem: Erect, quadrangular, and covered with stinging hairs (trichomes).
• Leaves: Opposite, ovate, with serrated edges and trichomes that contain histamine, serotonin, and formic acid.
• Flowers: Small, greenish, grouped in drooping inflorescences. The species is dioecious, meaning there are separate male and female plants.
• Roots: Rhizomatous and creeping, allowing rapid growth and expansion.
• Habitat: Prefers moist, nitrogen-rich soils and grows along forest edges, roadsides, and cultivated fields.

Chemical Composition

Nettle is rich in bioactive compounds that contribute to its numerous health benefits:

• Vitamins: High in vitamin A, vitamin C, B-complex vitamins, and vitamin K.
• Minerals: Contains significant amounts of iron, calcium, magnesium, silica, and potassium.
• Proteins: Contains a high percentage of plant proteins, making it a valuable nutritional source.
• Flavonoids: Such as quercetin and rutin, with antioxidant and anti-inflammatory effects.
• Phenolic Acids: Provide antioxidant and antimicrobial properties.
• Phytosterols: Beneficial for cardiovascular health and hormonal balance.
• Irritant Compounds: Histamine, serotonin, and acetylcholine, responsible for the stinging sensation when touched.

How to Cultivate Urtica dioica

Nettle is a hardy plant that grows easily:

1. Climate: Thrives in temperate climates and adapts to various environmental conditions.
2. Soil: Prefers rich, organic, moist, and well-drained soils.
3. Sunlight: Prefers partial shade but also grows well in full sun.
4. Watering: Requires moderate watering, avoiding waterlogging.
5. Propagation: Propagates via seeds or by dividing rhizomes.
6. Harvesting: Young leaves can be harvested in spring and summer, before flowering, for culinary and medicinal use.

Uses and Benefits

• Culinary Uses:

  • The leaves, once cooked or dried to neutralize their stinging effect, are used in soups, teas, fillings, and casseroles.
  • Traditionally consumed in many European cuisines for its high nutritional value.

• Medicinal Properties:

  • Anti-inflammatory: Used to relieve joint pain, arthritis, and rheumatism.
  • Diuretic and detoxifying: Supports kidney function and helps eliminate toxins.
  • Immune booster: Thanks to its high vitamin and mineral content.
  • Anti-anemic: Its high iron content makes it useful for treating anemia.
  • Metabolic regulation: Supports blood sugar control and digestive health.
  • Hair tonic: Nettle infusions are traditionally used to strengthen hair and prevent hair loss.

• Agricultural and Environmental Uses:

  • Natural fertilizer: Nettle macerate is an excellent plant tonic and natural pest repellent.
  • Biological pest control: Used as an organic insecticide in agriculture.

• Cosmetic Uses:

  • Nettle extract is used in shampoos and scalp treatments.
  • Applied for oily and acne-prone skin due to its astringent properties.

Applications

• Medical:

  • Used in teas, extracts, and supplements to support general health.
  • Ongoing studies explore its potential in treating benign prostatic hyperplasia (BPH) and metabolic disorders.

• Food Industry:

  • Added to natural supplements for overall well-being.
  • Commonly consumed as soup, infusions, and dried powder.

• Agriculture and Gardening:

  • Nettle macerate is a natural remedy for healthier and more resilient plants.

• Textile Industry:

  • Historically, nettle fibers were used to make durable fabrics.

Environmental and Safety Considerations

• Environmental Benefits:

  • Supports biodiversity by providing habitat and food for pollinators like butterflies and bees.
  • Helps improve soil fertility and can be used in land rehabilitation.

• Safety:

  • Contact with fresh leaves can cause a stinging skin reaction, which usually subsides within hours.
  • Excessive consumption may have strong diuretic effects, so moderate intake is recommended.

Studies

Medical

The leaf extract has been reported to prevent some of the effects of prostatic hyperplasia (1) and as an anti-inflammatory for rheumatoid arthritis. It has an anti-diabetic effect and is used for cardiovascular therapy for its bioactive compounds such as polyphenols, tri-terpenes, sterols, flavonoids and lectin that reduce blood glucose levels (2) with their anti-inflammatory, antioxidant, anti-hypertensive properties and can prevent many chronic and degenerative diseases. The efficacy of this edible plant with its stinging hairs has proved useful for its anti-haemorrhagic, analgesic, diuretic, nutritive, anti-asthmatic, astringent and depurative effects.

Phytochemical composition

The fresh leaves are used to treat allergies (3) and contain chlorogenic acid, malic acid, flavonoids such as rutin, quercetin, kaempferol while the root contains lignans, phytosterols, polysaccharides, coumarins.

Cosmetics

Cosmeceutical product for anti-dandruff and anti-hair loss lotions.

Hair conditioning agent. A large number of ingredients with specific purposes can co-exist in a hair shampoo: cleansers, conditioners, thickeners, mattifying agents, sequestering agents, fragrances, preservatives, special additives. However, the indispensable ingredients are the cleansers and conditioners as they are necessary and sufficient for hair cleansing and manageability. The others act as commercial and non-essential auxiliaries such as: appearance, fragrance, colouring, etc. Hair conditioning agents have the task of increasing shine, manageability and volume, and reducing static electricity, especially after treatments such as colouring, ironing, waving, drying and brushing. They are, in practice, dispersing agents that may contain cationic surfactants, thickeners, emollients, polymers. The typology of hair conditioners includes: intensive conditioners, instant conditioners, thickening conditioners, drying conditioners.

Food

The leaves of Urtica dioica are edible and are consumed in foods such as pesto, omelettes, soups, purees, pies, biscuits, jellies, jams, while the whole dried herb is included in teas, infusions and other preparations.

Other uses

Veterinary medical, textile industry

Typical commercial product characteristics Urtica Dioica Leaf Powder

The most relevant studies on the subject have been selected with a summary of their contents:

Urtica dioica studies

References_____________________________________________________________________

(1) Dhouibi R, Affes H, Ben Salem M, Hammami S, Sahnoun Z, Zeghal KM, Ksouda K. Screening of pharmacological uses of Urtica dioica and others benefits. Prog Biophys Mol Biol. 2020 Jan;150:67-77. doi: 10.1016/j.pbiomolbio.2019.05.008. 

Wagner H, Willer F, Samtleben R, Boos G. Search for the antiprostatic principle of stinging nettle (Urtica dioica) roots. Phytomedicine. 1994 Dec;1(3):213-24. doi: 10.1016/S0944-7113(11)80068-1. 

(2) El Haouari M, Rosado JA. Phytochemical, Anti-diabetic and Cardiovascular Properties of Urtica dioica L. (Urticaceae): A Review. Mini Rev Med Chem. 2019;19(1):63-71. doi: 10.2174/1389557518666180924121528. 

Dar SA, Ganai FA, Yousuf AR, Balkhi MU, Bhat TM, Sharma P. Pharmacological and toxicological evaluation of Urtica dioica. Pharm Biol. 2013 Feb;51(2):170-80. doi: 10.3109/13880209.2012.715172.

Abstract. Context: Medicinal plants are a largely unexplored source of drug repository. Urtica dioica L. (Urticaceae) is used in traditional medicine to treat diverse conditions. Objective: The present study describes the antidiabetic, antiinflammatory, antibacterial activity, and toxicological studies of Urtica dioica. Materials and methods: U. dioica leaves were subjected to solvent extraction with hexane, chloroform, ethyl acetate, methanol, and aqueous, respectively, and screened for antidiabetic (300 mg/kg bw by glucose tolerance test; GTT), antiinflammatory (200 mg/kg bw by rat paw edema assay) and antibacterial activities [by disc-diffusion and minimum inhibitory concentration (MIC) assays]. Toxicological studies were carried on Artemia salina and Wistar rats; phytochemical analyses were carried out, using chromatographic and spectroscopic techniques. Results: The aqueous extract of U. dioica (AEUD) significantly (p < 0.001; 67.92%) reduced the blood glucose level during GTT in Wistar rats with an effective dose of 300 mg/kg bw in dose-dependent studies. High-performance liquid chromatography with photodiode-array detection (HPLC-DAD) analysis showed the presence of hydroxycinnamic acid derivatives and flavonoids in AEUD. Hexane Fraction-2 (HF2) exhibited both antiinflammatory activity (48.83% after 3 h), comparable to that of indomethacin (53.48%), and potent antibacterial activity with MIC values ranging from 31.25-250 µg/mL against all the tested strains. Gas chromatography-mass spectrometry (GC-MS) analysis showed fatty acid esters and terpenes as the major constituents of HF2. Toxicity tests showed higher safety margin of all the solvent extracts with LC(50) > 1000 μg/mL each on A. salina. Discussion and conclusion: Our results showed that the U. dioica leaves are an interesting source of bioactive compounds, justifying their use in folk medicine, to treat various diseases.

(3) Upton, R. (2013). Stinging nettles leaf (Urtica dioica L.): Extraordinary vegetable medicine. Journal of herbal medicine, 3(1), 9-38.

Abstract. The efficacy and safety of herbal medicines are dependent upon the standards by which they are made and our knowledge base when prescribing them. Stinging nettles is a staple among Western herbalists and is widely used as a vegetable green, juice, tea, and freeze dried products, predominantly as a blood nourishing tonic and for seasonal rhinitis. The following botanical profile is excerpted from the American Herbal Pharmacopoeia® and Therapeutic Compendium.

Orčić D, Francišković M, Bekvalac K, Svirčev E, Beara I, Lesjak M, Mimica-Dukić N. Quantitative determination of plant phenolics in Urtica dioica extracts by high-performance liquid chromatography coupled with tandem mass spectrometric detection. Food Chem. 2014 Jan 15;143:48-53. doi: 10.1016/j.foodchem.2013.07.097. 

Pinelli P, Ieri F, Vignolini P, Bacci L, Baronti S, Romani A. Extraction and HPLC analysis of phenolic compounds in leaves, stalks, and textile fibers of Urtica dioica L. J Agric Food Chem. 2008 Oct 8;56(19):9127-32. doi: 10.1021/jf801552d.

Abstract. In the present study the phenolic composition of leaves, stalks, and textile fiber extracts from Urtica dioica L. is described. Taking into account the increasing demand for textile products made from natural fibers and the necessity to create sustainable "local" processing chains, an Italian project was funded to evaluate the cultivation of nettle fibers in the region of Tuscany. The leaves of two nettle samples, cultivated and wild (C and W), contain large amounts of chlorogenic and 2- O-caffeoylmalic acid, which represent 71.5 and 76.5% of total phenolics, respectively. Flavonoids are the main class in the stalks: 54.4% of total phenolics in C and 31.2% in W samples. Anthocyanins are second in quantitative importance and are present only in nettle stalks: 28.6% of total phenolics in C and 24.4% in W extracts. Characterization of phenolic compounds in nettle extracts is an important result with regard to the biological properties (antioxidant and antiradical) of these metabolites for their possible applications in various industrial activities, such as food/feed, cosmetics, phytomedicine, and textiles.

Devkota HP, Paudel KR, Khanal S, Baral A, Panth N, Adhikari-Devkota A, Jha NK, Das N, Singh SK, Chellappan DK, Dua K, Hansbro PM. Stinging Nettle (Urtica dioica L.): Nutritional Composition, Bioactive Compounds, and Food Functional Properties. Molecules. 2022 Aug 16;27(16):5219. doi: 10.3390/molecules27165219. 

Abstract. Stinging nettle (Urtica dioica L., Urticaceae) is commonly found in Asia, Africa, and Europe and has a long history of being used as food and traditional medicine. Recently, this plant is gaining attention as a highly nutritious food, where fresh leaves are dried and used as powder or in other forms. Leaves are rich in many bioactive compounds. This review aims to cover the traditional uses in food and medicine, as well as its nutritional composition, including its bioactive chemical constituents and reported food functional activities. Various bioactive chemical constituents have been isolated from stinging nettle to date, such as flavonoids, phenolic acids, amino acid, carotenoids, and fatty acids. Stinging nettle extracts and its compounds, such as rutin, kaempferol, and vitamin A, are also used for their nutritional properties and as anti-inflammatory and antioxidant agents. Future studies should focus on the proper formulation and stability testing of the functional foods containing stinging nettle and their detailed activities in clinical studies.

Đurović S, Micić D, Šorgić S, Popov S, Gašić U, Tosti T, Kostić M, Smyatskaya YA, Blagojević S, Zeković Z. Recovery of Polyphenolic Compounds and Vitamins from the Stinging Nettle Leaves: Thermal and Behavior and Biological Activity of Obtained Extracts. Molecules. 2023 Feb 28;28(5):2278. doi: 10.3390/molecules28052278.

Abstract. Stinging nettle (SN) is an extraordinary plant from the Urticaceae botanical family. It is well-known and widely used in food and folk medicine to treat different disorders and diseases. This article aimed to study the chemical composition of SN leaves extracts, i.e., polyphenolic compounds and vitamins B and C, because many studies ascribed high biological potency to these compounds and their significance in the human diet. Besides the chemical profile, the thermal properties of the extracts were studied. The results confirmed presence of many polyphenolic compounds and vitamins B and C. It also showed that the chemical profile closely correlated with the applied extraction technique. The thermal analysis showed that analyzed samples were thermally stable up to about 160 °C. Thermal degradation of samples UAE, MAE, and MAC took place in four steps, and sample SE in three steps. Altogether, results confirmed the presence of health-beneficial compounds in stinging nettle leaves and indicated the possible application of its extract in pharmaceutical and food industries as both a medicinal and food additive.