According to research results recently published in the Sept. 2007 issue of Medicine & Science in Sports & Exercise, quercetin—a flavonoid with antioxidant properties that’s found in several different types of fruit, including apples—helps reduce the incidence of upper respiratory tract infections (URTI).
The researchers investigated the effects of quercetin supplementation on incidence of URTI and exercise-induced changes in immune function by randomly supplementing the diets of 40 trained male cyclists with the flavonoid. The level of supplementation was equivalent to the level of quercetin found in 100 apples. Half of the group received a placebo to serve as a control. Quercetin was supplemented during the three weeks before and during a three-day period where the cyclists exercised for three hours a day. Supplementation was also continued for three days after the period of exercise.
Blood and saliva samples were collected before and after each of the three exercise sessions and analyzed. Although several aspects of immune function remained unaffected by supplementation, results showed that URTI incidence during the two-week postexercise period differed significantly between the quercetin-supplemented and placebo groups. This led the researchers to conclude that “quercetin versus placebo ingestion did not alter exercise-induced changes in several measures of immune function, but it significantly reduced URTI incidence in cyclists during the two-week period after intensified exercise.”