(American Physiological Society) Mice given quercetin, a naturally occurring substance found in fruits and vegetables, were less likely to contract the flu.

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.