Effects of repeated oral intake of a quercetin-containing supplement on allergic reaction: a randomized, placebo-controlled, double-blind parallel-group study.

OBJECTIVE: The present study aimed to investigate the effects of a 4-week repeated oral intake of a quercetin-containing supplement on allergen-induced reactions and relative subjective symptoms in Japanese adults who complained of discomfort in the eyes and nose. SUBJECTS AND METHODS: A randomized, placebo-controlled, double-blind parallel-group study was conducted on 66 subjects (22-78 years old) with allergic symptoms of pollinosis. The subjects were given the test product (200 mg quercetin) or the control product (vehicle) daily for 4 weeks. The Japanese Rhino-conjunctivitis Quality of Life Questionnaire (JRQLQ) scores and other tests were examined in each subject before and after starting the product intake. A new food-grade bioavailable formulation of quercetin, Quercetin phytosome®, was used. RESULTS: At 1:4 weeks after the start of the supplement intake, several scores of JRQLQ, including allergic symptoms, such as eye itching, sneezing, nasal discharge, and sleep disorder, were significantly improved in the quercetin-containing supplement group compared with the placebo group. Furthermore, the quality of life of these subjects significantly improved based on the original questionnaire and visual analog scale. Minor notable adverse effects were noted throughout the study. CONCLUSIONS: The results indicated that oral intake of quercetin-containing supplements might effectively reduce some allergy symptoms derived from pollinosis.