Quercetin and Allergies

What is Quercetin?

Quercetin, a flavonoid or bioflavonoid, is a plant phytochemical or pigment.

Quercetin Sources

Quercetin can be obtained through:

• Consuming foods rich in the compound, or from
• Herbs such as Ginkgo biloba and St. John’s wort, or
• By taking a supplement, typically in capsule or powder form.

Levels of quercetin in various foods can be seen below:

 Note: Original data source – USDA 2003. Food types included and figures cited vary between USDA versions released e.g. USDA 2007 and USDA 2011.

Recommended Daily Allowance of Quercetin

Although there is currently no formal recommended daily allowance (RDA) for quercetin, it has been estimated that an average US adult consumes between 25-50 mg daily.

Interestingly, the RDA of quercetin suggested by advocates of its usage (i.e. unofficial) varies considerably. A range anywhere between 200 mg to 800 mg is typical, with some suggesting up to a 1000 mg daily to treat allergies. However, given that high supplement doses of quercetin may have significant side effects, and taking into account the issue of bioavailability, foods rich in quercetin in its natural form may still provide an amount that is beneficial.

Function and Benefits of Quercetin

Quercetin is said to exhibit a number of qualities beneficial to one’s health. It may be associated with helping to prevent damage and promote a healthier brain, heart, immune system, kidney, liver and prostrate, whilst exhibiting anti-allergy, anti-cancer, anti-hypertensive, anti-inflammatory, antioxidant and antiviral qualities.

Evidence Concerning Quercetin Benefits

There has been some research looking at the validity of such claims but the studies have been relatively limited in scope and depth, often in-vitro (conducted outside body or organism) and have produced mixed results. Therefore, at present, the possible benefits of taking quercetin are largely circumstantial and anecdotal rather than confirmed scientifically.

Side Effects of Quercetin

Though quercetin seems to be generally tolerated well at lower, short-term doses, the more common side effects include headaches, tingling feet or hands and an upset stomach. When given intravenously, flushing, sweating and possible nausea and vomiting have been reported. Potentially serious side effects can include an allergic reaction and possible breathing difficulties, as well as kidney damage at higher dosages (greater than 1000 mg or 1 gram daily). Pregnant women and young children should not take quercetin and furthermore, due to possible interactions with other medication, anyone who is on anticoagulants, chemotherapy, cyclosporine, digoxin, fluoroguinolones or steroids should consult a practitioner before taking quercetin.

Quercetin and Allergies

Advocates of the use of quercetin supplements as a viable natural treatment for allergies point out the following properties exhibited by quercetin:

• Anti-histamine. By inhibiting or slowing up the release of histamine release from basophil and mast cells e.g. Middleton et al. 1981, Pearce et al. 1984.
• Anti-inflammatory. By impacting various chemical mediators or signaling molecules implicated in the pathogenesis of allergic diseases. For example, through inhibiting the enzymes lipoxygenase and phospholipase A2 that convert arachidonic acid to leukotrienes. Leukotrienes can be significantly more powerful than histamine (1000-10,000 times) as an allergy stimulator and bronchial constrictor. Furthermore, Rogerio et al. 2007 concluded that “Quercetin and isoquercitrin are effective eosinophilic inflammation suppressors, suggesting a potential for treating allergies.”

Thornhill and Kelly 2000 study concerning natural treatment of perennial allergic rhinitis commented that, “Urtica dioica, bromelain, quercetin, N-acetylcysteine, and vitamin C are safe, natural therapies that may be used as primary therapy or in conjunction with conventional methods.”

Those less convinced note that:

• Quercetin supplements are poorly absorbed and have low bioavailability. However, advocates report intestinal absorption is improved with bromelain (enzymes found in pineapples).
• The majority of research quoted by supporters of quercetin is either in-vitro (out of body e.g. “test tube” experiments) or involves animal and not human studies.
• There exists research that sheds doubt on the advocate’s claims. For example, with reference to allergic rhinitis, Jaber 2002 noted that, “there are no good clinical research data on the use of quercetin”. Also,  Loke et al. 2008,  suggested that, “Metabolic transformation has a profound effect on anti-inflammatory activity of flavonoids such as quercetin” i.e. a  “lack of association between antioxidant and lipoxygenase inhibitory activity.”