Wise Mind Herbs

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Stinging nettle - Urtica dioica

Nettle, primarily Urtica dioica (common/stinging nettle), has been used medicinally for centuries. This review examines contemporary scientific evidence regarding its therapeutic properties, active constituents, and clinical applications.

Botanical Information and Common Names

The Urtica genus primarily includes Urtica dioica (common stinging nettle), which is most frequently studied and used medicinally. Other species include Urtica urens (dwarf nettle), Urtica pilulifera (Roman nettle), and Urtica angustifolia (narrow-leaved nettle). These species are collectively known as nettles, stinging nettles, or common nettles. They belong to the Urticaceae family and are characterized by fine hairs (trichomes) containing irritating chemicals that cause a stinging sensation upon contact.

Plants sometimes confused with nettle include white dead-nettle (Lamium album), which despite its name, belongs to the mint family (Lamiaceae) and lacks stinging properties, and wood nettle (Laportea canadensis), which is related but belongs to a different genus.

Nettle Leaf: Therapeutic Properties and Applications

Nettle leaves are rich in flavonoids, carotenoids, vitamins (particularly A, C, K, and B complex), minerals (iron, calcium, magnesium, and potassium), amino acids, chlorophyll, and polyphenols. The leaves also contain bioactive compounds such as histamine, serotonin, acetylcholine, and formic acid in the stinging hairs.

Scientific evidence supports several therapeutic applications of nettle leaf:

• Allergic Rhinitis: Multiple randomized controlled trials have demonstrated that nettle leaf extract can reduce symptoms of seasonal allergies. There is moderate evidence for efficacy comparable to low-dose antihistamines, with fewer side effects.
• Anti-inflammatory Properties: In vitro and animal studies show that nettle leaf inhibits several inflammatory pathways, including NF-κB activation and prostaglandin synthesis. This may explain its effectiveness in treating osteoarthritis and rheumatoid arthritis symptoms.
• Antioxidant Activity: High polyphenol content contributes to significant free radical scavenging activity, potentially protecting against oxidative stress-related conditions.
• Blood Glucose Regulation: Several studies indicate that nettle leaf may help lower blood glucose levels, possibly through multiple mechanisms including inhibition of intestinal α-glucosidase and pancreatic α-amylase.
• Cardiovascular Benefits: Research suggests nettle leaf may help reduce blood pressure and improve lipid profiles, though the evidence is preliminary.
• Antimicrobial Effects: In vitro studies demonstrate activity against various bacteria and fungi, though clinical applications remain underexplored.

Nettle Root: Therapeutic Properties and Applications

Nettle root contains different bioactive compounds than the leaves, including β-sitosterol, scopoletin, sterols, lignans (particularly (-)-3,4-divanillyltetrahydrofuran), and polysaccharides. These compounds contribute to its distinct therapeutic profile:

• Benign Prostatic Hyperplasia (BPH): The strongest evidence for nettle root use is in treating BPH symptoms. Multiple clinical trials demonstrate improvements in urinary flow rate, post-void residual volume, and quality of life scores. Randomized controlled trials have found the use of nettle root can significantly improve International Prostate Symptom Scores compared to placebo.
• Prostate Cancer: Preliminary in vitro and animal studies suggest potential antiproliferative and pro-apoptotic effects against prostate cancer cells, though human clinical evidence is lacking.
• Immunomodulatory Effects: Some research indicates nettle root may influence T-cell activity and cytokine production, potentially benefiting autoimmune conditions.
• Anti-inflammatory Properties: Through different mechanisms than leaf extracts, nettle root demonstrates anti-inflammatory activity, particularly in prostate tissue.

Recommended Dosages and Standardization

Dosage recommendations from clinical studies vary by preparation method and intended therapeutic use:

• Nettle Leaf:
  • Allergic Rhinitis: 300-600 mg of freeze-dried extract daily, typically standardized to contain 1-2% plant silica.
  • Arthritis: 1200-1800 mg of dried leaf daily, often standardized to flavonoid or caffeoylmalic acid content (2-3%).
  • General Use: 4-6 g of dried leaf daily as tea (usually 2-3 cups).
• Nettle Root:
  • BPH: 120-600 mg of root extract daily, standardized to contain 0.7-1.0% β-sitosterol or 1% scopoletin.
  • Most commercial products use a 10:1 or 5:1 extract, corresponding to 1.2-6 g of dried root.

Most clinical studies utilize standardized extracts rather than whole plant material, which allows for more consistent dosing and more reliable results. However, standardization parameters vary across studies and commercial products, complicating direct comparisons.

Safety Profile: Side Effects and Contraindications

Nettle is generally recognized as safe when used at recommended dosages, though several side effects and contraindications should be noted:

• Common Side Effects: Mild gastrointestinal disturbances, allergic reactions (rare), and contact urticaria from handling fresh plant material.
• Drug Interactions: Potential interactions with diuretics, antihypertensives, hypoglycemic agents, and anticoagulants/antiplatelets due to possible additive effects.
• Contraindications: Pregnancy (due to potential uterine-stimulating effects), kidney disorders (due to diuretic action), and individuals with known allergy to plants in the Urticaceae family.
• Theoretical concerns exist regarding hormonal effects, particularly with nettle root, though clinical evidence of significant endocrine disruption is lacking.

High-Dose Studies and Knowledge Gaps

Few studies have examined doses substantially exceeding the therapeutic ranges mentioned above. Limited toxicological investigations in animal models suggest nettle has a high safety margin, with no observed adverse effects at doses several times higher than typically recommended for humans when adjusted for body weight.

A notable knowledge gap exists regarding the long-term effects of high-dose supplementation. Most clinical trials have been of relatively short duration (2-16 weeks), leaving questions about safety and efficacy of extended use. Additionally, dose-response relationships have not been comprehensively characterized for most indications, and optimal standardization parameters remain undetermined.

Research examining potential benefits of higher doses is particularly lacking for nettle leaf preparations, while nettle root extracts have been studied at various concentrations for BPH, with diminishing returns observed above 600 mg of standardized extract daily.

Conclusion

Scientific evidence most strongly supports the use of nettle root for BPH and nettle leaf for allergic rhinitis and inflammatory conditions. While traditional uses encompass a much broader range of applications, many of these remain inadequately investigated by modern clinical research methodologies. The generally favorable safety profile and preliminary evidence for multiple therapeutic actions warrant further investigation, particularly regarding optimal dosing regimens, standardization approaches, and long-term safety.

References

Ahangarpour, A., Mohammadian, M., & Dianat, M. (2012). Antidiabetic effect of hydroalcholic Urtica dioica leaf extract in male rats with fructose-induced insulin resistance. Iranian journal of medical sciences, 37(3), 181.

Domola, M. S., Vu, V., Robson‐Doucette, C. A., Sweeney, G., & Wheeler, M. B. (2010). Insulin mimetics in Urtica dioica: structural and computational analyses of Urtica dioica extracts. Phytotherapy research, 24(S2), S175-S182.

Đurović, S., Kojić, I., Radić, D., Smyatskaya, Y. A., Bazarnova, J. G., Filip, S., & Tosti, T. (2024). Chemical constituents of stinging nettle (Urtica dioica L.): A comprehensive review on phenolic and polyphenolic compounds and their bioactivity. International Journal of Molecular Sciences, 25(6), 3430.

Goswami, N. G., Koli, M., Singh, A., & Giri, D. (2022). Urtica dioica: An undervalued herb a comprehensive review. Journal of Pharmacognosy and Phytochemistry, 11(3), 169-173.

Lopatkin, N., Sivkov, A., Schläfke, S., Funk, P., Medvedev, A., & Engelmann, U. (2007). Efficacy and safety of a combination of Sabal and Urtica extract in lower urinary tract symptoms—long-term follow-up of a placebo-controlled, double-blind, multicenter trial. International Urology and Nephrology, 39, 1137-1146.

Mahboubi, M. (2020). Urtica dioica in the management of benign prostate hyperplasia (BPH). The Natural Products Journal, 10(5), 535-542.

Nahata, A., & Dixit, V. K. (2012). Ameliorative effects of stinging nettle (Urtica dioica) on testosterone‐induced prostatic hyperplasia in rats. Andrologia, 44, 396-409.

Roschek Jr, B., Fink, R.C., McMichael, M. and Alberte, R.S., 2009. Nettle extract (Urtica dioica) affects key receptors and enzymes associated with allergic rhinitis. Phytotherapy Research: An International Journal Devoted to Pharmacological and Toxicological Evaluation of Natural Product Derivatives, 23(7), pp.920-926.

Riehemann, K., Behnke, B., & Schulze-Osthoff, K. (1999). Plant extracts from stinging nettle (Urtica dioica), an antirheumatic remedy, inhibit the proinflammatory transcription factor NF-κB. FEBS letters, 442(1), 89-94.

Semalty, M., Adhikari, L., Semwal, D., Chauhan, A., Mishra, A., Kotiyal, R., & Semalty, A. (2017). A comprehensive review on phytochemistry and pharmacological effects of stinging nettle (Urtica dioica). Current Traditional Medicine, 3(3), 156-167.