Quercetin supplementation and upper respiratory tract infection: A randomized community clinical trial
Abstract
Quercetin in culture with pathogens exerts anti‐pathogenic activities, but little is known regarding quercetin's effects on upper respiratory tract infection rates (URTI). The purpose of this randomized, double‐blinded, placebo‐controlled trial was to measure the influence of two quercetin doses (500 and 1000 mg/day) compared to placebo on URTI rates in a community group (N=1002, ages 18 to 85 years). Subjects ingested supplements for 12 weeks and logged URTI symptoms on a daily basis using the Wisconsin Upper Respiratory Symptom Survey. No significant group differences were measured for URTI outcomes, or when analyzing separately by gender, BMI, and age categories. Regression analysis revealed that the strongest interaction effect with group status was self‐reported fitness level. A separate analysis of subjects ≥ 40 years of age rating themselves in the top half of the entire group for fitness level (N=325) showed lower URTI severity (36% reduction, P=0.020) and URTI total sick days (31% reduction, P=0.048) for the Q‐1000 group compared to placebo In summary, quercetin supplementation over 12 weeks had no significant influence on URTI rates or symptomatology compared to placebo for all subjects combined. A reduction in URTI was experienced in subjects ≥ 40 years of age ingesting 1000 mg quercetin/day and rating themselves as physically fit.
How strong is the evidence?
Evidence Hub reads this as a randomized trial, done in people. Its evidence level is 2 of 5 (High · randomized trial). Randomized trials of a reasonable size are the strongest single-study design. Reported size: 1,002 participants or records.
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