Quercetin and Allergies

Among the flavonoids, quercetin is possibly the most biologically active. Quercetin is the aglycone (noncarbohydrate portion) of rutin, quercetrin and other glycoside flavonoids. It is widely distributed in the plant kingdom including oak trees (Quercus spp.), onions (Allium cepa) and tea (Camellia sinensis). It has effects on many different enzymatic systems in the body, most of them via its interaction with the calcium-regulating enzyme calmodulin. Quercetin’s effect on allergies is unmatched by other natural substances. It inhibits phospholipase A (responsible for converting phospholipids into arachidonic acid), lipoxygenase (responsible for converting arachidonic acid into leukotrienes), platelet aggregation, and mast cell and basophil degranulation. Quercetin has been shown to bind to calcium/calmodulin complexes, preventing the influx of calcium into mast cells and basophils. This inhibition prevents the mast cells from destabilizing and degranulating, keeping histamine and other preformed mediators from being released. In fact, quercetin so consistently blocks calcium induced mast cells destabilization that researchers often use it in experiments as a control substance for such activity. The activity of quercetin has been well known for years, leading to the synthesis of similar compounds by pharmaceutical companies. One such compound, cromyln (the active ingredient in Intal), has been used as a mast cell stabilizer for years. The only problem is that cromyln cannot be absorbed orally and must me delivered as a powder through spinhalers or an aerosol inhaler. Even then, only 8% is absorbed in the respiratory tract leading to the need to take 2 metered dosages four times per day. Like most biologically active flavonoids, quercetin’s pharmacology is quite interesting. The absorption of quercetin is about 20-52% depending on the form. While this may seem quite low, the elimination of quercetin and its derivatives is very low, and high plasma levels are easily maintained with a regular supply of quercetin in the diet. Studies conducted in rats showed that more than 25% of the absorbed quercetin was localized in the lung tissue, an added benefit to combat allergy and associated asthma. While these radioactive studies have not been repeated in man, it is likely that similar results would be found. It has been known for some time that the concomitant administration of bromelain, an enzyme derived from the stem of the pineapple plant, can enhance the absorption of quercetin as well as other flavonoids such as rutin. An added benefit included with bromelain is its ability to block inflammatory pathways (fibrin and kinin) and decrease the viscosity of mucus in the lungs.

Patients should begin to take quercetin upon the first signs of allergen exposure. Since quercetin is prophylactic (stabilizing mast cells rather than blocking histamine) and will stay in the blood stream, initial doses should be 400-600 mg, three times per day, for the first 5-7 days. Symptom relief may begin in the first several hours. Once plasma levels are up, 200-400 mg per day should be sufficient through the rest of the allergy season. Quercetin is extremely safe, and has so many other benefits (antioxidant, anti-inflammatory, capillary stability etc.) it should make it the foundation of any natural approach to allergic rhinitis therapy.

While other botanical products have been used for allergic rhinitis over the years, most of these work as anti-allergic agents due to the high amount of quercetin in them. Among them, garlic, onion, and green tea are the most popular.