PURPOSE: Quercetin, a flavonoid found in fruits and vegetables, is a strong antioxidant with anti-inflammatory, antimicrobial, and immune-modulating properties. The purpose of this study was to investigate the effects of long-term quercetin supplementation on innate immune function and inflammation in human subjects.
STUDY DESIGN: Female subjects (N=120, ages 30-79 years) were recruited from the community and randomized to one of three groups, with supplements administered using double-blinded procedures: Q-500 (500 mg/day quercetin, N=38), Q-1000 (1000 mg/day quercetin, N=40), or placebo (N=42). Subjects ingested two soft chew supplements twice daily during the twelve-week study period. Fasting blood samples were obtained pre- and post-study and were analyzed for plasma quercetin, interleukin (IL)-6, tumor necrosis factor (TNF)-a, and leukocyte subset cell counts. Natural killer cell activity (NKCA) and lymphocyte subsets were assessed on a subset of seventy-four subjects. Granulocyte oxidative burst activity (GOBA) and phagocytosis were assessed on sixty-four subjects. Eighteen subjects had overlapping data.
RESULTS: Quercetin supplementation at 500 and 1000 mg/day increased plasma quercetin (interaction effect, P<0.001) compared to placebo but had no significant influence on blood leukocyte or lymphocyte subset concentration, plasma IL-6 or TNF-a concentration, NKCA, GOBA, or granulocyte phagocytosis. NKCA was inversely correlated with BMI (r=-0.25, P=0.035) and body fat percentage (r=-0.38, P=0.001), and positively correlated with self-reported physical fitness level (r=0.24, P=0.032).
CONCLUSIONS: Results from this double-blinded, placebo-controlled, randomized trial indicate that quercetin supplementation at 500 and 1000 mg/day for twelve weeks significantly increased plasma quercetin levels but had no influence on measures of innate immune function or inflammation in community-dwelling adult females
