BioZine: Substance Found in Fruits and Vegetables May Reduce Chance of Flu

September 3, 2008

Weekly News UpdateSubstance Found in Fruits and Vegetables May Reduce Chance of Flu

In a recent study published by The American Physiological Society, researchers found that mice given quercetin had a smaller chance of catching the flu. The researchers also found that stressful exercise increased the likelihood of contracting flu in the mice. When the mice that had exercised were given quercetin, however, the researchers found that the mice were less susceptible to the flu—quercetin effectively canceled out the negative effects of stressful exercise.

What is quercetin?

Quercetin is a substance that is naturally found in fruits and vegetables. It is an example of a flavonol, a type of flavonoid. Flavonoids are substances found within plants that produce pigments in some flowers and protect the plant from attack by insects or microbes.

Foods rich in quercetin include red grapes, red onions, tea, and berries such as blueberries. Previous studies have indicated that quercetin is an effective anti-inflammatory agent and helps to prevent the processes that cause inflammation. Studies have also shown that quercetin, when combined with ultrasound therapy, works to inhibit the growth of cancerous tumors.

Blueberries are an example of a fruit rich in quercetin. (Photo Credit: USDA)

Quercetin and the Flu

In this most recent study, researchers based at the University of South Carolina and Clemson University studied the relationship between stressful exercise and susceptibility to flu in mice. In the experiment, the researchers studied four groups of mice. Two groups exercised to fatigue on a treadmill for three days in a row to imitate a short episode of stressful exercise. One group of exercising mice was given quercetin; the other was not. The two remaining groups of mice did not exercise. One of the non-exercising groups of mice was given quercetin; the other was not. Next, all four groups of mice were exposed to the common flu virus.

The results of the experiment were five-fold. First, mice that experienced stressful exercise were more likely to catch the flu. Second, the mice that exercised caught the flu sooner than the mice that had not exercised. Third, mice that exercised and were given quercetin had nearly the same rate of illness as the mice that did not exercise. Fourth, those mice that did not exercise, or that did exercise but took quercetin, experienced the same severity of flu symptoms. And fifth, the mice that did not exercise but were given quercetin experienced protective effects from the supplement.

How these results in mice relate to humans is less understood. In one study involving humans, it was shown that, following three consecutive days of stressful exercise, those who had taken quercetin were less likely to suffer from illnesses than those who did not take the supplement. However, further research is needed to fully understand how quercetin affects humans and whether or not its affects are the same for humans as they are for mice.