Substance found in fruits and vegetables reduces likelihood of the flu

Mice given quercetin, a naturally occurring substance found in fruits and vegetables, were less likely to contract the flu, according to a study published by The American Physiological Society. The study also found that stressful exercise increased the susceptibility of mice to the flu, but quercetin canceled out that negative effect.

Quercetin, a close chemical relative of resveratrol, is present in a variety of fruits and vegetables, including red onions, grapes, blueberries, tea, broccoli and red wine. It has been shown to have anti-viral properties in cell culture experiments and some animal studies, but none of these studies has looked specifically at the flu.

The study, "Quercetin reduces susceptibility to influenza infection following stressful exercise," was carried out by J. Mark Davis, E.A. Murphy, J.L. McClellan, and M.D. Carmichael, of the University of South Carolina and J.D. Gangemi of Clemson University. The study appears in the current issue of the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology.

The study was conducted using mice, but if quercetin provides a similar benefit for humans, it could help endurance athletes, soldiers and others undergoing difficult training regimens, as well as people under psychological stress, according to Davis.

Study builds on previous research

"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," Davis said.

Earlier mouse studies have found that stressful exercise can increase susceptibility to upper respiratory infections, although it is not yet clear if the same is true for humans. There was also preliminary information that mice may be more susceptible to the flu when they exercise to fatigue. The researchers in the current study hypothesized that exercise would increase the chance of the mice getting the flu but that quercetin would counteract the increased risk.

Davis and his colleagues examined four groups of mice. Two groups performed three consecutive days of running to fatigue on a treadmill to mimic a short period of stressful exercise. One group of runners received quercetin, the other did not.

The remaining two groups did not exercise. One non-exercise group received quercetin while the other did not. All four groups were then exposed to a common flu virus, H1N1.

The researchers found that:

-- Stressful exercise increased susceptibility to the flu. The mice that exercised to fatigue for three days were more likely to develop the flu than the mice that did not exercise (91% versus 63%).
-- The mice that exercised developed the flu much sooner than those that did not (6.9 days versus 12.4 days).
-- Mice that exercised and took quercetin had nearly the same rate of illness as those that did not exercise. In other words, quercetin canceled out the negative effect of stressful exercise.
-- The severity of the symptoms among those mice that either did not exercise or those that exercised but took the quercetin was about the same.
-- Quercetin had protective effects for the mice that did not exercise.

Although this study was done with mice, a recent human study found that people who took quercetin suffered fewer illnesses following three days of exhaustive exercise compared to those who did not. Unlike the mouse study, the humans were not inoculated with a virus.

"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."

Source: American Physiological Society

Related stories:

In space, a cluster of health dangers
Space shuttle commander Christopher Ferguson and his crew took a small but crucial step for space travel in the past two weeks, enlarging the International Space Station so it can house six astronauts instead of three.
Team identifies 13 new tumor-suppressor genes in liver cancer
Over the years, hunting for cancer-related genes and understanding how they work has been an important, although time-consuming, exercise. At Cold Spring Harbor Laboratory (CSHL), five different research groups have now combined their expertise to speed up the rate of discovering cancer-related genes and validating their function in living animals.
Calorie restriction and exercise show breast cancer prevention differences in postmenopausal women
Scientists at the University of Texas at Austin have identified pathways by which a reduced-calorie diet and exercise can modify a postmenopausal woman's risk of breast cancer.
Exercise increases brain growth factor and receptors, prevents stem cell drop in middle age
A new study confirms that exercise can reverse the age-related decline in the production of neural stem cells in the hippocampus of the mouse brain, and suggests that this happens because exercise restores a brain chemical which promotes the production and maturation of new stem cells.
Researchers present new theory that may lead to effective heart failure treatments
Do the biological underpinnings of heart failure share more in common with cancerous tumors than other cardiovascular diseases? Research presented at American Heart Association meeting may show why heart failure treatments fail.
Scientists develop a new strategy to fight obesity
The antibody works against the gastric hormone ghrelin (pronounced "grell-in"), which has been linked to weight gain and fat storage through its metabolic actions. These findings point towards a potentially novel treatment for obesity that would interfere directly with the some of the biological mechanisms determining weight.
Study may explain exercise-induced fatigue in muscular dystrophies
A University of Iowa study suggests that the prolonged fatigue after mild exercise that occurs in people with many forms of muscular dystrophy is distinct from the inherent muscle weakness caused by the disease.
Genes that control cell death fingered in age-related hearing loss
Several genes that play a role in how our body's cells normally auto-destruct may play a role in age-related hearing loss, according to research published online in the journal Apoptosis – a journal devoted to the topic of cell suicide, or programmed cell death.

News discussion:

Medicine & Health news