Nettle – Addressing Allergies Through Inflammation
Nettle (Urtica dioica) is a familiar and loved nourishing herb amongst herbalists and natural practitioners alike. Nettle leaves are specifically admired and utilized for their beneficial effects on symptoms of allergic rhinitis. It was only recently that the specific compounds associated with its anti-allergenic activity were fully identified.
Surprisingly, the ancient use of nettle was mainly for helping arthritic joints. Instead of being dosed orally, the fresh herb was actually flailed against the limbs to increase circulation in a method known as “urtication”. It was documented that Roman soldiers utilized fresh nettles in this way to increase warmth in their extremities while in colder climates.1
For many years, it was hypothesized that the reason nettle was effective for allergies and allergic rhinitis was due to its anti-inflammatory effects. A double-blind, placebo controlled trial conducted in 1990 showed that 300 mg of freeze-dried nettle daily was reported by patients as being more efficacious for resolving allergy symptoms than their traditional medication.2 However, this was a small study and further research is worth conducting.
The in vitro studies that were conducted on nettle extracts recently identified the aspects of nettle which explain its similar effect to conventional allergy medication. The main actions are H1 inhibition, mast cell tryptase inhibition, COX-1/COX-2 inhibition and hematopoietic prostaglandin D2 synthase inhibition (HPGDS).3 The H1-receptor antagonism and negative agonist action prevents histamine from binding to its receptor, blocking a cascade that results in histamine release, and ultimately preventing allergic symptoms.
The H1-receptor antagonism and negative agonist action prevents histamine from binding to its receptor, blocking a cascade that results in histamine release, and ultimately preventing allergic symptoms.
As most of the active constituents identified in nettle do not cross the blood brain barrier and likely act on peripheral receptors. It, therefore, would be unlikely to cause drowsiness. This may make nettle a more attractive option than OTC medications like diphenhydramine (another H1-antagonist), which cross the blood brain barrier and do have sedative effects. Components of nettle were also revealed to effectively inhibit mast cell tryptase, which would block degranulation of mast-cells and stop pro-inflammatory mediators that cause allergy symptoms. Nettle also has COX-1 and COX-2 inhibitory activity as well as HPGDS activity. This activity blocks upstream processes of proinflammatory pathways and formation of prostaglandins involved in causing allergy symptoms.
Another study demonstrated that the following bioactive components—adenine, synephrine, osthole, and nicotinamide—are the ones crucial to the anti-inflammatory and anti-allergenic processes mentioned above. These compounds can be detected in serum and urine after consuming a nettle lozenge (200mg)4, indicating their absorption and excretion. As these compounds are all related to improving inflammatory disorders, their discovery in urine and serum after a dose of nettle supports the use of nettle for relieving allergy symptoms associated with inflammation.
It is a lovely occurrence when traditional wisdom is supported by modern science, especially when it reflects what is seen in clinical practice: a wonderful plant that can safely help relieve hay fever symptoms.
- Upton R. Stinging Nettles leaf (Urtica dioica L.): Extraordinary vegetable medicine. Journal of Herbal Medicine. 2013;3(1):9-38. doi:10.1016/j.hermed.2012.11.001.
- Mittman P. Randomized, Double-Blind Study of Freeze-Dried Urtica dioica in the Treatment of Allergic Rhinitis. Planta Medica. 1990;56(01):44-47. doi:10.1055/s-2006-960881.
- Roschek B, Fink R, McMichael M, Alberte R. Nettle extract (Urtica dioica) affects key receptors and enzymes associated with allergic rhinitis. Phytotherapy Research. 2009;23(7):920-926. doi:10.1002/ptr.2763.
- Ayers S, Roschek Jr B, Williams J, Alberte R. Pharmacokinetic analysis of anti-allergy and anti-inflammatory bioactives in a nettle (Urtica dioica) extract. Online Journal of Pharmacology and Pharmacokinetics. 2008;5:6-21.