Dietary quercetin supplementation is not ergogenic in untrained men

Abstract

Quercetin supplementation increases muscle oxidative capacity and endurance in mice, but its ergogenic effect in humans has not been established. Our study investigates the effects of short-duration chronic quercetin supplementation on muscle oxidative capacity; metabolic, perceptual, and neuromuscular determinants of performance in prolonged exercise; and cycling performance in untrained men. Using a double-blind, pretest-posttest control group design, 30 recreationally active, but not endurance-trained, young men were randomly assigned to quercetin and placebo groups. A noninvasive measure of muscle oxidative capacity (phosphocreatine recovery rate using magnetic resonance spectroscopy), peak oxygen uptake (Vo(2peak)), metabolic and perceptual responses to submaximal exercise, work performed on a 10-min maximal-effort cycling test following the submaximal cycling, and voluntary and electrically evoked strength loss following cycling were measured before and after 7-16 days of supplementation with 1 g/day of quercetin in a sports hydration beverage or a placebo beverage. Pretreatment-to-posttreatment changes in phosphocreatine recovery time constant, Vo(2peak,) substrate utilization, and perception of effort during submaximal exercise, total work done during the 10-min maximal effort cycling trial, and voluntary and electrically evoked strength loss were not significantly different (P > 0.05) in the quercetin and placebo groups. Short duration, chronic dietary quercetin supplementation in untrained men does not improve muscle oxidative capacity; metabolic, neuromuscular and perceptual determinants of performance in prolonged exercise; or cycling performance. The null findings indicate that metabolic and physical performance consequences of quercetin supplementation observed in mice should not be generalized to humans.

Quercetin and Endurance Exercise Capacity

“…Nine studies were published in peerreviewed joumals. Four studies reported being fianded by a commercial interest (13,32,40,41), and two were funded by a federal agency (Table 1). Seven studies used a withinsubjects crossover experimental research design, with the other four using a randomized controlled trial with two independent groups.…”

“…In studies (21,47) that measured V02max or performance in the same subjects across multiple time points during the treatment (quercetin administration), standardized mean differences and variances were averaged across these time points. In studies that evaluated more than one experimental factor level, e.g., quercetin dosages of 1000 and 1400 mgd~' for independent subject groups compared with a single placebo group (40) or if the two outcomes of endurance exercise performance and V02max were measured in the same subjects (13,14,47), the ES was calculated for each comparison or outcome, respectively, and the mean was used as the study's ES. Meta-analyses were performed using a random-effects model that accounts for true interstudy variation in effects as well as for random error within each study (4).…”

“…Some studies report increased endurance exercise capacity in humans after ingestion of quercetin (14,33,41), whereas most others fail to find statistically significant benefits in endurance exercise capacity (i.e., endurance exercise performance or aerobic capacity) (2,9,13,21,22,40,47,49). Possible reasons for the inconsistent findings among these studies may include the range of subject fitness levels (i.e., potentially eliciting greater quercetin benefits for lower fit subjects), differences in plasma quercetin concentration obtained via the various supplementation protocol/supplement types, differences in research design, and/or inadequate statistical power.…”

Polyphenol Supplementation: Benefits for Exercise Performance or Oxidative Stress?

“…The relatively recent advent of polyphenol supplementation for exercise studies has necessarily resulted in a fairly narrow range of doses. Nonetheless, a variety of polyphenol sources has been tested (see Table 4) [37–51]. On the one hand this is interesting, but on the other does not allow for much comparison as only quercetin testing has resulted in several studies.…”

“…Of these, three peer-reviewed studies measured changes in V O 2max , and although mean changes indicated improvements ranging from 2.3 to 7.5 %, the changes were not all statistically significantly different from placebo. The duration of supplementation did not separate the statistical differences between studies and, although the doses differed, this also did not seem to affect the outcome: after 5 days of supplementation with 1,000 mg/day, V O 2max increased by 7.5 % [37], and after a similar duration of supplementation (7 days) resulted in a lower percentage improvement of 3.9 %, which was statistically significant [38]. The main difference between the two studies was a possible dose–response effect because the second study using half the dose (500 mg/day) of the first also revealed approximately half the percentage increase in V O 2max of that of the first study mentioned.…”