Quercetin may not be a household word -- yet.
But a study by researchers at the University of South Carolina’s Arnold School of Public Health shows that the powerful antioxidant/anti-inflammatory compound found in fruits and vegetables significantly boosts endurance capacity and maximal oxygen capacity (VO2max) in healthy, active but untrained men and women.
The findings of the study – one of the first in humans to examine the energy-boosting effects of quercetin – are reported in the International Journal of Sports Nutrition and Exercise Metabolism, published online Wednesday (June 24).
Dr. Mark Davis, the study’s lead author and a professor of exercise science, said the fatigue-fighting and health properties of quercetin – found in the skins of red apples, red onions, berries and grapes – have implications not only for athletes and soldiers whose energy and performance are tested to the extreme, but also for average adults who battle fatigue and stress daily.
“The natural, biological properties of quercetin that include powerful antioxidant and anti-imflammatory activity, as well as the ability to boost the immune system and increase mitochondria (the powerhouse of the cell) in muscle and brain is great news for those who often think that they’re too tired to exercise,” Davis said.
“While there’s no magic pill to make people get up and move, or to take the place of regular exercise, quercetin may be important in relieving the fatigue that keeps them sedentary and in providing some of the benefits of exercise,” he said. “We believe that this could be a major breakthrough in nutrition.”
For the study, funded in part by the U.S. Department of Defense, 12 participants were randomly assigned to one of two treatments. Half were given 500 milligrams of quercetin twice a day in Tang for seven days. The other subjects drank Tang with placebos. After the seven days of treatment, during which the subjects were told not to alter their physical activity, the participants rode stationary bicycles to the point of fatigue.
Researchers also tested their additional VO2max, one of the most important measures of fitness. Then the participants received the opposite treatment for another seven days before riding the bicycle to the point of fatigue and VO2max tests. Neither the participants nor the research staff knew who received the quercetin Tang or the placebo Tang, and all subjects took part in the quercetin and placebo treatments.
“The participants were healthy, relatively active, college-age students, but they were not physically trained athletes, and they were not taking part in a regular exercise training program,” he said.
The results: After taking quercetin for only seven days, the participants had a 13.2 percent increase in endurance and a 3.9 percent increase in VO2max.
“These were statistically significant effects that indicate an important improvement in endurance capacity in a very short time,” Davis said. “Quercetin supplementation was able to mimic some of the effects of exercise training.
Although the study did not examine why the results were so dramatic, Davis said pre-clinical data suggest that quercetin may increase the mitochondria in brain and muscle cells. He likened the mitochondria to the “powerhouse of the cell,” producing most of its energy. Mitochondria in brain and muscle also are believed to be fundamentally important in battling age-related dementia, obesity, diabetes and cardiovascular dysfunction.
“One of the most important biological mechanisms for increasing endurance is increasing the mitochondria,” said Davis. “More mitochondria in the brain and muscle would enhance both mental and physical energy, as well as provide a better ability to fight other diseases in which mitochondrial dysfunction are hallmarks.”
Quercetin also appears to have valuable properties to fight inflammation, which has been linked to health problems such as colon cancer and heart disease. Davis’ research group has recently received a National Institutes of Health grant to study quercetin’s effects on colon cancer and others are pending that involve breast cancer.
“If the findings of this study and others on the biological mechanisms of quercetin are confirmed in future clinical studies, the implications go beyond improvements in endurance,” he said. “We may find that quercetin may work in conjunction with regular physical activity as an ally in preventing and treating diabetes, obesity and cardiovascular diseases and the degenerative diseases of aging.”