Monday, November 28, 2011

Quercetin supplementation: does it enhance performance?

Quercetin is classified as a flavonoid, a substance found in considerable amounts in fruits and vegetables. Basic research has showed that quercetin may act as antioxidant and anti-inflammatory. Recently, two more roles of quercetin ingestion on human body have been investigated: 1) its biological role in alleviating the negative effects of intense training on immune system, 2) its effect in enhancing sports performance.

Does quercetin supplementation enhance performance?
Claims on the beneficial effect of quercetin supplementation in performance are based on the fact that quercetin has been shown to enhance the number of mitochondria in animal studies. Let me remind you that mitochondria are the main sites for aerobic energy production. What is the truth? Although studies showed elevated mitochondrial biogenesis with quercetin supplementation in animals, no such strong evidence exists in humans.

Besides mitochondrial biogenesis, quercetin may also act with a mechanism similar to caffeine. Again, no such strong evidence exists in humans. Some studies have showed performance improvements after 1-3 weeks of quercetin supplementation in untrained subjects. However, most studies with elite and trained subjects failed to show improved performance with quercetin supplementation. One explanation might be that trained subjects have already maximized their mitochondrial aerobic capacity with training.

 In the December 2011 issue of the Medicine & Science in Sports & Exercise, Kressler and colleagues published a meta-analysis on the effect of quercetin ingestion on endurance capacity. Their conclusion was that “On average, quercetin provides a statistically significant benefit in human endurance capacity (VO2max and endurance exercise performance), but the effect is between trivial and small.

To summarize, there is no strong evidence that quercetin supplementation enhances endurance performance in well-trained athletes.

Can it be used as a means to prevent illness after intense training?
Although evidence is limited in humans, it seems that quercetin supplementation can strengthen some aspects of the immune system and thus protect athletes from some illnesses during periods of intense training.

Current use
Quercetin is available as a sports supplement claimed to enhance performance. Most studies involve supplementation with 1,000 mg daily, distributed in 2 doses. Typical supplementation period is 1-3 weeks but it may extend up to 6 weeks.

For more reading
  • ·     Kressler et al. Quercetin and endurance exercise capacity: a systematic review and meta-analysis. Med Sci Sports Exerc. 43:2396-2404, 2011.
  • ·     Nieman et al. Quercetin reduces illness but not immune perturbations after intensive exercise. Med Sci Sports Exerc. 39:1561-9, 2007.
  • ·     Nieman et al. Quercetin's influence on exercise performance and muscle mitochondrial biogenesis. Med Sci Sports Exerc. 42:338-45, 2010.
  • ·     Rodriguez et al. American Dietetic Association; Dietitians of Canada; American College of Sports Medicine. Position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and athletic performance. J Am Diet Assoc. 109:509-27, 2009.

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