Modern Indications of an Ancient Herb –

An article on Stinging Nettle (Urtica dioica) use in Complementary and Alternative Medicine by Carla Gemeinhardt 

INTRODUCTION

People have gathered wild plants in the temperate ecosystems of the Pacific West Coast of Canada for thousands of years, preparing and celebrating their diversity and use for food and medicine. Every spring, as with the Nuxalk First Nations before me (1), my family and I gathered stinging nettle for food.

Like coastal British Columbia, Ireland enjoys a temperate climate where annual rainfall is high and wild nettle is abundant and simple to gather. It is also simple to prepare and versatile in its use. This year, as I have done every year since moving to Dublin, I have welcomed the green of an Irish spring by harvesting nettles. This year however, as I searched for an Irish nettle soup recipe, I recognized a growing number of publications on the therapeutic effects of nettle from regions across Europe and North America.

A review of literature is presented here, in part to spur renewed interest in this historically significant herb and in part to elucidate its benefits and potential application to disease treatment and prevention. In keeping with many traditional claims, stinging nettle has been found to produce diuretic effects, alleviate inflammation associated with arthritis, reduce lower urinary tract symptoms (LUTS) associated with benign prostatic hyperplasia (BPH), and improve symptoms of allergic rhinitis. Complimentary and alternative health care, including use of herbal remedies, is an exciting opportunity for practitioners to share in the holistic care of their patients. Moreover, perhaps patient engagement and participation in preventative healthcare can be improved upon through education and interest in local, nutrient rich, and delicious foods such as the wild stinging nettle.

COMPLEMENTARY AND ALTERNATIVE MEDICINE

Complementary and alternative medicine (CAM) includes natural products, mind-body medicine, and manipulative and body-based practices. Today, many people in the US use CAM in pursuit of health and well-being. The 2007 US National Health Interview Survey revealed that approximately 38% of US adults use CAM (2) and in Australia and Europe this proportion reaches 50% (3). Approximately 30-50% of Europeans use CAM as self-support and 10-20% have seen a CAM physician/practitioner within the previous year (4).

Many countries throughout the world are creating regulatory bodies aimed at research and education for patients and practitioners. The American National Center for Complementary and Alternative Medicine (NCCAM) for example is the federal government agency whose role is to explore CAM using scientific methods and to build an evidence base regarding their safety and efficacy. In Canada this role is carried out by the Natural Health Products Directorate of Health Canada. Many organizations exist in Europe, including the European Committee for Homeopathy (ECH) and the European Council of Doctors for Plurality in Medicine (ECPM).

“Complementary medicine” refers to use of CAM together with conventional “allopathic” medicine. Most use of CAM by Americans for example is complementary. “Alternative medicine” refers to use of CAM in place of conventional medicine. “Integrative medicine” combines both conventional and CAM treatments for which there is established safety and efficacy (2). “Natural products” include use of herbal medicines (botanicals), vitamins, minerals, and probiotics, many of which are sold as dietary supplements (2).

Treatments based on herbs cannot all be considered alternative or unconventional though, as the larger percentage of allopathic medications is derived from plants and herbs. In contrast, many herbal constituents function synergistically and these processes are not yet identified.

HARVESTING AND PREPARING WILD NETTLE

Look for a perennial plant growing around 1-4 feet tall in areas such as creek sides and along fields. The leaves are heart-shaped and finely toothed (figure 1). When collecting stinging nettle, remember that fine hairs on the leaves and stems will irritate the skin. While wearing gloves, harvest carefully by clipping the young tips and leaves (not the larger, older leaves, which can be tough and bitter) (figure 2). Once back in the kitchen, rinse leaves in cool water to remove any dirt and bugs. From here, one can steam them (about 2 minutes, rendering the hairs inactive) and prepare them as you like: as a side dish with a little salt, pureed in a green smoothie, or blended into a delicious pesto. You can also bake them into bread, steep the fresh leaves for tea, or brew them into beer or cordial. Personally, I like to steam them and then freeze them, condensed, for use in soups or sauces throughout the summer. Also, the water remaining after steaming can be enjoyed as a tea or used as a broth.

Nettle leaves have a delicious flavour comparable to spinach when cooked. It is a rich source of vitamins and antioxidants, including vitamins A, C and E. It is also a great source of vitamins D and K and minerals such as iron, calcium, magnesium, potassium, phosphorous, chlorine, sulphur, and copper (5,6). The root reportedly contains several compounds including scopoletin, sitosterol, oleanolic acid, isolectins, polysaccharrides, and various lignans. The actual active principle is still unknown (3).

BACKGROUND

Stinging nettle herb has been used since ancient times. Greek physicians reported nettle leaf to have diuretic and laxative effects and cited it as useful in asthma, pleurisy, and for the treatment of spleen-related illness.

In traditional African medicine the herb is used for nosebleeds, excessive menstruation, and to treat internal bleeding. In India, the Ayurvedic Pharmacopoeia lists stinging nettle herb for uterine hemorrhage, cutaneous eruptions, eczema, and nosebleed.

In Germany, the leaves and seeds are extensively researched for this application, as are the roots for the relief of LUTS secondary to BPH. Stinging nettle is used in German homeopathy for treatment of urticaria, herpes, eczema, hypersensitivity reactions in the skin and joints, and burns.

In North American aboriginal bands nettle is used it as an antirheumatic drug. It is also used as a gynecological aid and taken as an aqueous infusion during childbirth to relax the muscles. The plant juice is also taken by pregnant women who are past their due dates and the tips of the plant are chewed by women during labour.

Today in the United States, stinging nettle herb is used as a component in a wide range of dietary supplements and formulas used to treat hay-fever and other allergies (7,8).

STINGING NETTLE IN MEDICINE

Scientific and common names: Urtica dioica, Urtica urens, Urticae radix, common nettle, nettle weed, stinging nettle, small nettle (8,9).

Nettle can be taken orally in the form of capsules, tablets, tinctures, juice, or tea. Various formulas are described in the literature depending on the indications. Nettle also comes in the form of an ointment or cream for topical application. As mentioned, nettle is well described in homeopathy (3,10) however for the purposes of this article I will focus only on nettle as an herbal preparation.

POTENTIAL INTERACTIONS AND ADVERSE EFFECTS

Though the internal use of nettles is not associated with any documented adverse effects (3), it is worth mentioning potential drug interactions.

Firstly, stinging nettle may affect coagulation, and interfere with antiplatelet and anticoagulant medication, including Warfarin, Clopidogrel, and Aspirin. It may also lower blood pressure and affect outcome of medications such as ACE inhibitors, beta blockers, and calcium channel blockers (8). Secondly, because nettle acts as a diuretic, it can increase the effects of other diuretics, such as Furoseminde and Hydrochlorothiazides, raising the risk of dehydration. Thirdly, medication in the management of diabetes may also pose risks for interaction, as nettle may lower blood sugar (11).

Symptoms of acute overdose have not been reported. Of note, because nettle can alter the menstrual cycle and may contribute to miscarriage, pregnant women should not use it (3,11).

CURRENT LITERATURE ON EFFICACY OF STINGING NETTLE

In vitro studies have demonstrated anti-inflammatory effects, immune-modulatory activity, and inhibition of platelet aggregation. Further, influence on insulin secretion and inhibition of protease activity have been found. Describing the many in-vitro studies carried out thus far is beyond the scope of this review. The European Medicines Agency Assessment Report on Nettle however lists these concisely and provides an overall assessment of study outcomes if the reader wishes to review these in more detail (7,12).

Osteoarthritis  

Five open, multicentric studies have been carried out on patients with arthritic or rheumatic complaints using a preparation containing a dry hydro-alcoholic extract of nettle leaf, given twice per day 670 mg (9.648 g dried leaf per day.) In one of these studies, Ramm and Hansen (13) investigated the above preparation (Rhema-Hek) over 3-weeks in 152 patients. Patients were treated with either Rhema-Hek alone or in combination with Diclofenac. Pain symptoms improved in 70% of patients with combination therapy by at least one third. In patients receiving only nettle leaf extract, pain decreased by 43%. The authors suggested mono-therapy with Rheuma Hek was a suitable treatment only for weaker rheumatic complaints. 78% of physicians rated the combination therapy good or very good. The tolerability of combined therapy was qualified good or very good by 95% of physicians and patients. Ramm and Hansen (14) also carried out a 3 week post-marketing surveillance study in 1528 patients showing Rheuma-Hek to be very well tolerated and effective in alleviating rheumatic complaints. The dose of current NSAIDs used in parallel with the nettle could be reduced in 42.8% of the patients and could be stopped in 19.75% of patient (7).

Diuretic Effects

Liquid extracts sold with this claim have been on the German market since at least 1976. As mentioned it has been researched, results have been positive and subjects have experienced few side effects (7).

In an open study, the expressed juice of stinging nettle (Urtica dioica, U. urens) was found to prevent recurrence of renal stones and to provide supportive treatment of rheumatic complaints. It was administered for 12 weeks to 114 patients with excellent tolerability (15). Further, medium potency diuresis was confirmed by a preliminary uncontrolled clinical trial suggesting nettle can relieve oedema caused by congestive heart failure (16).

A publication in the World Journal of Urology (17) concludes that further research is required before any definitive recommendations can be made about the use of nettle in urological treatments. Initial information, however, was found to support the idea that botanicals do act as diuretics and further research is warranted.

Relief of lower urinary tract symptoms due to benign prostatic hyperplasia

BPH is a common complaint in aging men with the most common symptoms being LUTS. Treatment of this disorder has typically been aimed at relieving obstructive symptoms and several botanical therapies have been well documented for this. Unfortunately, no trials have yet been published assessing the impact of these therapies on long-term risk of obstruction or incidence of surgical treatment (18). Auffenberg et al. (19) also note that little regulation exists over the consistency of herbal compounds prepared for use in BPH, meaning products from different manufacturers may not contain the same ‘‘active ingredient’’ and are not subject to strict monitoring for strength, purity, or safety.

Yarenell (17) does however summarize in vitro studies aimed at illuminating the exact constituents of nettle and their effects. The root contains lignans, reputed to directly or indirectly prevent testosterone binding to sex hormone-binding globulin (SHBG). Aqueous root extracts were found to inhibit binding of SHBG to its receptor on prostate cells. Root extracts may weakly inhibit 5-alpha-reductase and inhibit aromatase. As mentioned, polysaccharides and lectins have been implicated as important constituents in the root, mediating inflammation and growth factor activities within the prostate.

Chrubasika et al. (20) state summarize that a total of approximately 40,000 men suffering from BPH have been treated with various nettle root preparations in 34 clinical studies (most open and uncontrolled) of which 25 found improvement. Others either found no improvement or no difference from placebo. Further, laboratory studies have shown stinging nettle to be comparable to finasteride in slowing the growth of certain prostate cells. Unlike finasteride however the herb does not decrease prostate size (21).

In clinical research, a 6-month, double-blind, placebo-controlled, randomized, partial crossover, comparative trial of Urtica dioica against placebo in 620 patients concluded Urtica dioica to have beneficial effects in treatment of symptomatic BPH. No appreciable change was seen in the placebo group and serum prostate specific antigen and testosterone levels were unchanged in both groups. A modest decrease in prostate size as measured by transrectal ultrasonography in Urtica dioica group though there was no change in the prostate volume at the end of study with placebo. No side effects were identified (22). Another double-blind trial found the combination of nettle and saw palmetto herb equally effective at reducing symptoms and increasing uroflow scores with fewer adverse effects than finasteride over one year (23).

It is proposed that one of the primary mechanisms of why herbal agents are effective in BHP is the anti-inflammatory effect (24,25). In an open-label extension of a randomized, double-blind clinical trial, the long-term efficacy and tolerability of a fixed combination of Sabal fruit extract and Urtica root extract per capsule were investigated in elderly men with moderate or severe LUTS caused by BPH. Efficacy measures included the assessment of LUTS [International Prostate Symptom Score ((I-PSS) self-rating questionnaire] and uroflow and sonographic parameters. Between baseline and end of observation the I-PSS total score was reduced by 53%, peak and average urinary flow increased by 19%, and residual urine volume decreased by 44%. Treatment was concluded to be clinically beneficial (26). In contrast, another study found no beneficial outcome when nettle was combined with Pygium africanum (27).

In summary, though more rigorous trials are needed, existing data do suggest that stinging nettle can reduce LUTS in men with BPH. Its efficacy compared to alpha-adrenergic antagonists, finasteride, saw palmetto, and placebo should certainly be more deeply investigated (17)

Allergic Rhinitis

Allergists are often confronted with patients using CAM treatments for their chronic conditions making it imperative that they become familiar with the scientific literature, as an understanding of CAM therapies is needed to establish appropriate guidelines for their use (28,29).

Medicinal extracts of Urtica dioica contain polysaccharides and caffeic malic acid, which are found in all parts of the plant and are stated to relieve rhinoconjunctivitis symptoms in-vivo as well as provide anti-inflammatory effects in-vitro (3). Further, an extract of Urtica dioica showed in vitro inhibition of several key inflammatory events that cause the symptoms of seasonal allergies. These include antagonist and negative agonist activity against Histamine-1 receptor and inhibition of mast cell tryptase, preventing degranulation and release of a host of pro-inflammatory mediators. The nettle extract also inhibits prostaglandin formation through inhibition of Cyclooxygenase-1 (COX-1), Cyclooxygenase-2 (COX-2), and Hematopoietic Prostaglandin D2 synthase (HPGDS), central enzymes in pro-inflammatory pathways (30).

In a double-blind randomized clinical trial comparing the effects of a freeze-dried preparation of Urtica dioica with placebo in allergic rhinitis, Urtica doica was rated higher than placebo in global assessments though was rated only slightly higher when comparing subject diary data (31).

Hay fever

One preliminary human study suggests that nettle capsules helped reduce sneezing and itching in people with hay fever. Researchers consider this may be due to reduction of histamine production in response to an allergen. The authors again call for further research to confirm the antihistamine properties of nettle (11).

CONCLUSION

The therapeutic claims of nettle as an herbal product are abundant, yet as medical practitioners, allopathic or naturopathic, it is vital that these claims are clearly understood and best treatment methods practiced. Ideally, efficacy of CAM modalities should be established with randomized, double-blind, placebo-controlled trials, including monitoring of adverse-effects and interactions with allopathic, prescribed medication. Based on the increasing integration of CAM by patients our future roles as health care providers and advocates should include greater awareness and understanding of these medical modalities. The increasing use of CAM necessitates standardization and education. I would argue for the incorporation of alternative and complementary medical practices into medical school curricula and residency programs, particularly here in Ireland. A greater dispersion of knowledge about and interest in research on botanical medicine can improve on these relatively inexpensive, effective, and safe therapies.

REFERENCES

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2. National Center for Complimentary and Alternative Medicine. [Internet] [updated 2008 Nov; cited 2011 Apr 18]. Available from: http://nccam.nih.gov/health/whatiscam/

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4. The regulatory status of Complementary and Alternative Medicine for medical doctors in Europe. CAMDOC Alliance. [Internet] 2009 [cited 2011 Apr 17]  Available from: http://www.epha.org/IMG/pdf/CAMDOCRegulatoryStatus.pdf

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7. Natural Health Products Ingredients Database. Monograph: Stinging Nettle. Assessment report on Urtica dioica L., Urtica urens L., folium. European Medicines Agency; 2010 Jan. Report No.:EMA/HMPC/508013/2007

8. The Natural Health Products Directorate of Health Canada. Monograph. Stinging Nettle. [Internet] 2008 [updated 2008 Jan30; cited 2011 Apr 17]. Available from: http://webprod.hc-sc.gc.ca/nhpid-bdipsn/monoReq.do?id=166&lang=eng

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21. Konrad L, Hans- MüllerH, LenzC, LaubingerH, AumuellerG,  Lichius JJ. Antiproliferative Effect on Human Prostate Cancer Cells by a Stinging Nettle Root (Urtica dioica) Extract. Planta Med. 2000; 66(1): 44-47. doi: 10.1055/s-2000-11117

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31 Mittman P. Randomized, double-blind study of freeze-dried Urtica dioica in the treatment of allergic rhinitis. Planta Med. 1990 Feb;56(1):44-7.