A 12-week supplementation with quercetin does not affect natural killer cell activity, granulocyte oxidative burst activity or granulocyte phagocytosis in female human subjects

Br J Nutr. 2010 Sep;104(6):849-57. doi: 10.1017/S000711451000156X. Epub 2010 May 26.


Quercetin, a flavonoid found in fruits and vegetables, is a strong antioxidant with anti-inflammatory, antimicrobial and immune-modulating properties. The purpose of the present study was to investigate the effects of long-term quercetin supplementation on innate immune function and inflammation in human subjects. Female subjects (n 120; aged 30-79 years) were recruited from the community and randomised to one of three groups, with supplements administered using double-blinded procedures: 500 mg quercetin/d (n 38), 1000 mg quercetin/d (n 40) or placebo (n 42). Subjects ingested two soft chew supplements twice daily during the 12-week study period. Fasting blood samples were obtained pre- and post-study and were analysed for plasma quercetin, IL-6, TNF-alpha and leucocyte subset cell counts. Natural killer cell activity (NKCA) and lymphocyte subsets were assessed in a subset of seventy-four subjects. Granulocyte oxidative burst activity (GOBA) and phagocytosis were assessed in sixty-four subjects. Eighteen subjects had overlapping data. Quercetin supplementation at two doses compared with placebo increased plasma quercetin (interaction effect; P < 0.001) but had no significant influence on blood leucocyte subsets, plasma IL-6 or TNF-alpha concentration, NKCA, GOBA or 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). In summary, results from the present double-blinded, placebo-controlled, randomised trial indicated that quercetin supplementation at 500 and 1000 mg/d for 12 weeks significantly increased plasma quercetin levels but had no influence on measures of innate immune function or inflammation in community-dwelling adult females.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Antioxidants / pharmacology*
  • Body Composition / immunology
  • Body Mass Index
  • Dietary Supplements*
  • Double-Blind Method
  • Female
  • Granulocytes / drug effects*
  • Granulocytes / metabolism
  • Humans
  • Killer Cells, Natural / drug effects*
  • Killer Cells, Natural / metabolism
  • Middle Aged
  • Phagocytosis / drug effects*
  • Physical Fitness / physiology
  • Plant Extracts / pharmacology
  • Quercetin / blood
  • Quercetin / pharmacology*
  • Respiratory Burst / drug effects*


  • Antioxidants
  • Plant Extracts
  • Quercetin