title: Quercetin and endurance exercise capacity: a systematic review and meta-analysis.
abstract: Quercetin is a dietary flavonoid purported to improve human endurance exercise capacity. However, published findings are mixed.
  
  
  OBJECTIVE
  The study's purpose was to perform a systematic review of the literature and meta-analysis to examine whether quercetin ingestion increases endurance exercise capacity.
  
  
  METHODS
  A search of the literature was conducted using the key words quercetin, performance, exercise, endurance, and aerobic capacity. Eleven studies were identified as meeting the inclusion criteria providing data on 254 human subjects. Across all studies, subject presupplementation VO(2max) ranged from 41 to 64 mL·kg(-1)·min(-1) (median = 46), and median treatment duration was 11 d with a median dosage of 1000 mg·d(-1). Effect sizes (ES) were calculated as the standardized mean difference, and meta-analyses were completed using a random-effects model.
  
  
  RESULTS
  The ES calculated for all studies combining VO(2max) and endurance performance measures indicates a significant effect favoring quercetin over placebo (ES = 0.15, P = 0.021, 95% confidence interval = 0.02-0.27), but the magnitude of effect is considered between trivial and small, equating to a ∼2% [corrected] improvement of quercetin over placebo. Using a subgroup meta-analysis comparing quercetin's effect on endurance exercise performance versus VO(2max), no significant difference was found (P = 0.69). Meta-regression of study ES relative to subjects' fitness level or plasma quercetin concentration achieved by supplementation was also not significant.
  
  
  CONCLUSIONS
  On average, quercetin provides a statistically significant benefit in human endurance exercise capacity (VO(2max) and endurance exercise performance), but the effect is between trivial and small. Experimental factors that explain the between-study variation remain to be elucidated.
authors: School of Applied Physiology, Georgia Institute of Technology, Atlanta, GA 30332-0356, USA.
authors: Jochen
authors: J
authors: Kressler
authors: Melinda
authors: M
authors: Millard-Stafford
authors: Gordon L
authors: GL
authors: Warren