What do apples and onions have to do with exercise?  Quercetin.  Quercetin, a polyphenolic flavonoid of which apples and onions serve as good sources, was the topic of a study published online last month in the International Journal of Sport Nutrition and Exercise Metabolism.  The study investigated the possible effects of quercetin on exercise in humans.  

     Results of animal studies indicate that quercetin may improve performance.  These studies have found that it provides a variety of health benefits due to its antioxidant and anti-inflammatory properties.  These studies have also indicated that quercetin increases the number of mitochondria (the "powerhouse of the cell" from which the cell gets most of its energy) in the brain and muscles.  Research regarding these effects in humans is lacking.

     A team of investigators from the University of South Carolina's Arnold School of Public Health, led by Dr. Mark Davis, investigated the effects of quercetin consumption on maximal aerobic capacity (a measure of how physically fit you are) and exercise endurance in twelve healthy and active, but not highly trained, college students.  The study involved two testing trials, each a week long.  For one of the weeks, 6 of the subjects consumed 500 mg of quercetin dissolved in Tang twice a day, while the remaining 6 drank Tang with a placebo twice a day.  At the end of the week the subjects performed an endurance ride at a constant workload to the point of fatigue and a graded exercise test to evaluate aerobic capacity.  For the second trial, the subjects were crossed over to the other supplement and then performed the exercise tests at the end of the week.  Therefore, all subjects were exposed to both the quercetin and placebo conditions.  Neither the subjects nor the researchers knew which drink was being consumed during the trial periods.

     The results of the study revealed that maximal aerobic capacity was positively effected by quercetin supplementation.  Maximal aerobic capacity was greater by about 3.9% with the quercetin dose when compared to the placebo trial.  Endurance capacity was also enhanced by quercetin supplementation, with an increase of about 13.2% being noted.

     The researchers did not specifically investigate the means by which quercetin enhances exercise performance, but they offer the following hypotheses:

• It could increase mitochondrial biogenesis (assumption based on animal research).   An increase in the number of mitochondria is a primary factor in improving exercise endurance.
• Its antioxidant property may play a role in protecting the cell membranes from oxidative damage, subsequently delaying muscular fatigue.
  
• Its "caffeine-like psychostimulant effect" may delay fatigue by blocking adenosine receptors in the brain.

     The investigators indicate that further research is needed in this area to fully understand the role that quercetin plays in improving exercise performance as well as in health promotion and disease prevention overall.  Although eating a well balanced diet that includes a variety of fresh fruits and vegetables is your best bet for optimal health, you can increase the amount of quercetin in your diet by consuming the following foods:

• Apples
• Onions
• Cherries
• Berries
• Buckwheat

Resources:

International Journal of Sport Nutrition and Exercise Metabolism, 2009, 20, 1-13 "The Dietary Flavonoid Quercetin Increases VO2max and Endurance Capacity," Davis, M.J. et al.

The Encyclopedia of Healing Foods, 2005, p. 670, Murray, M.