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You are here: Home Physical Fitness Training & Exercise Performance Degraders Does quercetin improve endurance performance?

Does quercetin improve endurance performance?

Can quercetin—one of the most abundant flavonoids—affect endurance?

From the Field

What are quercetin's effects on endurance?

Overview

Quercetin and performance

B.L.U.F.*

Current available evidence does not support claims that quercetin can improve endurance performance.

Background

Quercetin is a naturally occurring flavonoid present in a variety of fruits, vegetables, nuts, and spices. It seems to benefit human health through its antioxidant, anticarcinogenic, anti-inflammatory, and cardioprotective properties.

Myths and Claims

Many believe that quercetin confers performance benefits for endurance activities, in addition to the established health benefits.

Facts

It is still possible that quercetin may influence endurance performance. However, the available scientific literature is inconsistent. For instance, although some studies found improvements in endurance performance, others did not. Of the few studies reporting an increase in endurance performance, an associated improvement in aerobic fitness was not seen. In addition, interpretation of results must be made with caution because of various confounders. For instance, in one study, results showed a very slight improvement in performance with quercetin supplementation, but no change in aerobic fitness, and the initial training status of the subjects and intensity of the performance tests were probably too high to elicit observable changes in the latter. Another study had subjects consume quercetin bars for a period of five days. This duration may have been too short to elicit any performance improvements. From the available evidence, it is difficult to determine conclusively if quercetin improves endurance performance. More research studies are required.

Cautions

No serious adverse effects have been reported in the scientific literature from using quercetin supplements at recommended doses (£ 1,000 mg daily). However, many quercetin supplements contain other ingredients that could produce unwanted results.

Summary for Military Relevance

Endurance capacity is a major component of total physical fitness, and enhanced capacities contribute to mission effectiveness, reduced injuries, and more rapid recovery. Thus, enhancing endurance performance is of great importance to the military. Although quercetin may offer one such avenue, its effectiveness on endurance performance cannot be supported at this time. Nonetheless, quercetin taken at recommended dose is safe, has other health benefits, and has no adverse effects of direct military concern.



* Bottom Line Up Front

Research Summary

Quercetin and performance

Key Points

  • Quercetin is one of the most abundant flavonoids and occurs in a variety of fruits, vegetables, nuts, and spices.
  • Quercetin has antioxidant, anticarcinogenic, anti-inflammatory, and cardioprotective properties.
  • Daily dietary intakes of quercetin range from as low as five to as much as 500 milligrams depending on whether the peel portion of the food is consumed.
  • The typical dosage of supplemental quercetin reported in literature is 1,000 milligrams (or less) daily.
  • No serious adverse effects have been reported in the scientific literature from using quercetin supplements at the recommended doses.
  • Current evidence suggests that quercetin may not improve endurance performance.

Background

Quercetin, one of the most abundant natural flavonoids, is present in a variety of fruits, vegetables, nuts, and spices; it is also the most frequently studied flavonoid [1,2]. It has attracted much attention for its potential antioxidant, anticarcinogenic, anti-inflammatory, and cardioprotective properties. Due to its possibly favorable effects, quercetin intake has been suggested to benefit human health. In addition to the health benefits conferred by ingestion of quercetin, it has been proposed that quercetin improves endurance performance, but examination of the scientific literature indicates that quercetin may not do so. This research brief provides an overview of the scientific literature on quercetin and its effects on endurance performance, as well as claims, facts, and how this information may be translated into the military community.

Synthesis and mechanism of action. Quercetin is ingested primarily through dietary sources such as berries, apples, onions, broccoli, kale, red wine, and tea [2,3]. The amount of quercetin from habitual food intake ranges from five to 40 milligrams per day [3] but can be as much as 200-500 milligrams per day when consumption of fruits and vegetables is high, especially if the peel of the fruit is eaten [3]. Quercetin is also available as a dietary supplement.

Evidence suggests that quercetin from foods and supplements is absorbed into the bloodstream through the intestines and excreted in the urine. However, the mechanisms of absorption are not fully understood [4]. What is known is that dietary quercetin is mainly present as glycosides and its phenolic hydroxyl groups, which act as electron donors and are responsible for its free radical–scavenging activity [4].

With respect to endurance performance, quercetin may exert its effects through an increase in mitochondrial biogenesis, antioxidant activity, antagonizing adenosine receptors, and possible psychostimulant properties [4-6]. Animal studies suggest that quercetin stimulates mitochondrion biogenesis via intracellular pathways [6]. An increase in muscle mitochondrion content is one of the physiological adaptations to endurance exercise training and serves an important role in the observed increase in maximal oxygen uptake (VO2max), oxidation of fat relative to carbohydrate, lactate threshold, and resistance to fatigue [6].

Benefits. As a rule, flavonoids are antioxidants. Hence, quercetin has free radical–scavenging properties. In addition, quercetin has anticarcinogenic and anti-inflammatory properties [6], with the potential benefits of reducing the occurrence of cardiovascular disease and cancers [7].

Myths and/or Claims

Many believe that quercetin confers performance benefits for endurance activities, in addition to the established health benefits.

Facts and Evidence

It is possible that quercetin may influence endurance performance via mechanisms mentioned previously. In support of this claim, Davis et al. [6] observed a modest increase in VO2max after seven days of quercetin feeding to healthy untrained college students. This study also reported a substantial increase in the time to reach fatigue during prolonged cycling. However, examination of current scientific evidence suggests that quercetin may not improve endurance performance. Recent studies by Ganio et al. [8], Cureton et al. [9], and Bigelman et al. [10] found no significant changes in VO2max and other related variables after several days of quercetin supplementation. Ganio and his colleagues found no significant differences in maximal aerobic fitness in 11 untrained, sedentary men and women who consumed quercetin-supplemented food bars (1000 milligrams per day) for six days. Cureton et al. used supplementation over a period of seven to 16 days in 30 recreationally active men and found no significant improvement in prolonged exercise and cycling performance. Likewise Bigelman et al. investigated the effects of six weeks of quercetin supplementation on physical performance in 58 healthy, moderately trained men and women from the Army and Air Force Reserve Officers’ Training Corps (ROTC) programs and found no improvement in aerobic fitness or other physical performance tests. Another study that investigated the effect of acute quercetin ingestion on endurance exercise performance in the heat found no performance improvements [5].

A few studies have reported improvements in performance, but without a concomitant increase in VO2max, the gold standard for assessing endurance or aerobic fitness in humans. Nieman et al. [11] examined the influence of a two-week quercetin supplementation period in untrained young adults. In this randomized, double-blind, placebo-controlled, counter-balanced, crossover trial, subjects performed a 12-minute treadmill time trial after 60 minutes of exercise at moderate intensity. The results showed a modest increase in the time trial performance: distance covered in 12 minutes increased by approximately three percent. However, no significant improvements in VO2max were noted [11]. In another study, MacRae and Mefferd [12] investigated the effects of six weeks of antioxidant supplementation plus quercetin versus antioxidant supplementation minus quercetin on 30 km (18.6 mi) time-trial-cycling performance in 11 highly trained male cyclists. The results of this double-blind, randomized, crossover study showed that the supplement containing quercetin improved the time-trial performance by approximately three percent [12]. However, there was no significant improvement in VO2max, possibly due to the training status of the subjects and intensity of the time trials. The elite cyclists could have reached a ceiling in modifiable physiological factors, such as mitochondrion size, antioxidant capacity, and aerobic capacity [6]. Furthermore, the time trials were performed at such high intensities that multiple systems could have contributed to energy production. However, other studies [8-10] without these confounders still did not observe improvements in VO2max. Taken together, it seems that quercetin supplementation may not have the endurance-enhancing effects previously attributed to it.

Cautions

No serious adverse effects have been reported in the scientific literature from using quercetin supplements at recommended doses (£1,000 mg daily) [1]. However, there is no long-term human data available on the potential toxicity of quercetin [1]. Although there are no clear interactions of quercetin with other dietary supplements or medications [1], the Natural Medicines Comprehensive Database reports that quercetin may interact moderately with cyclosporine, several cytochrome P450 substrates, P-glycoprotein substrates, quinolone antibiotics, and warfarin [13]. Nonetheless, consumers should note that many quercetin dietary supplements currently on the market may contain more than just quercetin; supplements may also contain mixtures of compounds and hidden ingredients. Using supplements tested by a third party such as United States Pharmacopeia (USP) or NSF International for quality will help ensure product grade.

Military Relevance

Optimizing the performance of Warfighters is essential to ensure combat readiness. Endurance capacity is a major component of total physical fitness; enhanced capacities contribute to mission effectiveness, reduced injuries, and rapid recovery. Thus, enhancing endurance performance is of great importance to the military. It has been suggested that quercetin might offer one such avenue, but it now appears that its effectiveness on endurance performance may be minimal or non-existent. Nevertheless, available studies maintain that quercetin, if taken at recommended doses, is safe for general health benefits and has no adverse effects of direct military concern.

Summary

Current evidence suggests that quercetin may not provide any endurance performance benefits. However, available evidence suggests that taking quercetin at recommended doses is safe and has many other health benefits. Consumers who choose to use quercetin supplements should use those tested for quality by a third-party verification program to ensure product grade.

References

Quercetin and performance

References

  1. Greenwood M, Oria M. Use of Dietary Supplements by Military Personnel: Natl Academy Pr; 2008.
  2. Quercetin. Alt Med Rev. 1998;3(2):140-3.
  3. Harwood M, Danielewska-Nikiel B, Borzelleca JF, Flamm GW, et al. A critical review of the data related to the safety of quercetin and lack of evidence of in vivo toxicity, including lack of genotoxic/carcinogenic properties. Food Chem Toxicol. 2007;45(11):2179-205.
  4. Murota K, Terao J. Antioxidative flavonoid quercetin: implication of its intestinal absorption and metabolism. Arch Biochem Biophys. 2003;417(1):12-7.
  5. Cheuvront SN, Ely BR, Kenefick RW, Michniak-Kohn BB, et al. No effect of nutritional adenosine receptor antagonists on exercise performance in the heat. Am J Physiol Regul Integr Comp Physiol. 2009;296(2):R394-401.
  6. Davis JM, Carlstedt CJ, Chen S, Carmichael MD, et al. The dietary flavonoid quercetin increases VO(2max) and endurance capacity. Int J Sport Nutr Exerc Metab. 2010;20(1):56-62.
  7. Ross JA, Kasum CM. Dietary flavonoids: bioavailability, metabolic effects, and safety. Annu Rev Nutr. 2002;22:19-34.
  8. Ganio MS, Armstrong LE, Johnson EC, Klau JF, et al. Effect of quercetin supplementation on maximal oxygen uptake in men and women. J Sports Sci. 2010;28(2):201-8.
  9. Cureton KJ, Tomporowski PD, Singhal A, Pasley JD, et al. Dietary quercetin supplementation is not ergogenic in untrained men. J Appl Physiol. 2009;107(4):1095-104.
  10. Bigelman KA, Fan, E.H., Chapman, D.P., Freese, E. C., Trilk, J.L., Cureton, K.J. Effects of Six Weeks of Quercetin Supplementation on Physical Performance in ROTC Cadets. Mil Med. 2010;175(10):791-8.
  11. Nieman DC, Williams AS, Shanely RA, Jin F, et al. Quercetin's influence on exercise performance and muscle mitochondrial biogenesis. Med Sci Sports Exerc. 2010;42(2):338-45.
  12. MacRae HS, Mefferd KM. Dietary antioxidant supplementation combined with quercetin improves cycling time trial performance. Int J Sport Nutr Exerc Metab. 2006;16(4):405-19.
  13. Quercetin. Therapeutic Research Faculty; 2010. http://naturaldatabase.therapeuticresearch.com/home.aspx?cs=dod&s=ND. Accessed 1 September 2010.