Quercetin Clinical Evidence

Allergology International

Toru H, et al. Preventative effect of a flavonoid, enzymatically modified isoquercitrin on ocular symptoms of Japanese cedar pollinosis. 2009 Sep:58(3):373-82.

Can quercetin help relieve symptoms in subjects allergic to Japanese cedar pollen?

Quercetin is a flavonoid that appears in many foods such as tea, apples and onions. Flavonoids are phytochemicals with anti-allergenic effects.

Study Type:
Human clinical intervention trial

Study Design:
Parallel group, double-blind, placebo-controlled. Subjects took quercetin or placebo for 8 weeks, starting 4 weeks prior to the start of pollen season. Researchers measured the subjects’ symptoms, ADL (Activities of Daily Life) scores, usage of drugs daily and QOL (Quality of Life) every four weeks. Blood tests were performed before and after the study to measure levels of flavonoids and IgE (an antibody associated with allergic hypersensitivity).

24 subjects with Japanese cedar pollen allergies

100 mg/day for 8 weeks

Ocular symptoms were significantly improved for the treatment group; quercetin was significantly better than placebo in reducing both total ocular symptom score and ocular congestion score. Nasal symptoms did not improve significantly versus placebo.

Intake of quercetin glycoside EMIQ proved to be effective for the relief of ocular symptoms caused by Japanese cedar pollinosis.

Quercetin Mechanism of Action:

Quercetin, a bioflavonoid found in red wine, apples and grapefruit, has been found to prevent mast cells from releasing histamine — a substance that triggers allergic responses such as watery secretions, itchiness, and redness. Quercetin also blocks the release of leukotrienes — signaling molecules that cause redness, pain, and swelling. Of various flavonoids studied, quercetin was one of the most active inhibitors of histamine release.