Apples and onion may protect athletes from flu
Quercetin, the compound most commonly associated with onions, may boost the immune system and protect against flu, according to results of a study with mice.
Researchers from the University of South Carolina and Clemson University also report that stressful exercise increased the mice’s susceptibility to flu, but quercetin was found to negate these effects.
The findings are published in the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, and build on results from last year which reported the flavonoid found could help reduce illnesses in people who have carried out extensive exercise.
If the results can be reproduced in humans it could see the flavonoid positioned for sports nutrition for helping endurance athletes, soldiers and others undergoing difficult training regimens, as well as people under psychological stress, said lead researcher Mark Davis.
"Quercetin was used because of its documented widespread health benefits, which include antiviral activity, abundance in the diet and reported lack of side effects when used as a dietary supplement or food additive," said Davis.
Companies have already started to take advantage of the flavonoid. Energy drink FRS Plus containing quercitin, and aimed at reducing fatigue and boost overall performance by fighting free radicals in the body, was launched in 2002 .
The researchers started with the premise that strenuous exercise increases the risk for upper respiratory tract infections.
Four groups of mice were used in the study - two groups performed three consecutive days of running to fatigue on a treadmill: One group of runners received quercetin (12.5 mg/kg), the other did not.
The remaining two groups did not exercise, but one received quercetin, while the other did not. All four groups were then exposed to the common flu virus H1N1.
The researchers found that the running mice not fed the quercetin were at an increased susceptibility to infection (91 per cent), while quercetin was found to offset infection risk (63 per cent).
Moreover, mice that exercised developed the flu much sooner than those that did not (6.9 days versus 12.4 days).
The same rate of illness in the mice that exercised and took quercetin was approximately same as those that did not exercise, added the researchers. This suggested that quercetin supplementation cancelled out the negative effects of the stressful exercise.
“These data suggest that short-term quercetin feedings may prove to be an effective strategy to lessen the impact of stressful exercise on susceptibility to respiratory infection,” wrote the researchers.
"This is the first controlled experimental study to show a benefit of short-term quercetin feedings on susceptibility to respiratory infection following exercise stress," said Davis. "Quercetin feeding was an effective preventive strategy to offset the increase in susceptibility to infection that was associated with stressful exercise."
The potential health benefits of quercetin have included reduction of blood pressure in people with hypertension. Researchers from the University of Utah reported results of a randomised, double-blind, placebo-controlled, crossover study last year that found a daily 730 milligram supplement of quercetin led to significant reductions in blood pressure.
The study, said to be the first to report the blood pressure-lowering activity of this flavonol, was published in the Journal of Nutrition (Nov. 2007, Vol. 137, pp. 2405-2411).
Source: American Journal of Physiology-Regulatory, Integrative and Comparative Physiology Volume 295, Pages R505-R509"Quercetin reduces susceptibility to influenza infection following stressful exercise"Authors: J.M. Davis, E.A. Murphy, J.L. McClellan, M.D. Carmichael, J.D. Gangemi