The literature reveals a paradoxical response of the immune and host defense systems
to endurance exercise: apparent stimulation following long-term regular training and
suppression in response to acute exposure to exhaustive endurance exercise. Several
epidemiological surveys have confirmed a clinical manifestation of immunosuppression
in the form of increased incidence of upper respiratory tract infection symptoms following
participation in competitive marathon and ultramarathon running events. Prerace training
status and racing intensity have been related to the incidence of this symptomatology
during the post-race fortnight. Nutritional intervention studies have shown the antioxidant
nutrient, vitamin C, to be effective in reducing the incidence of upper respiratory
tract infection symptoms following competitive distance events. Laboratory studies
have revealed this vitamin to be the first line of defense in neutralizing the auto-oxidative
activity of phagocytes. It is hypothesized that exercise-induced neuroendocrine stimulation
of the oxidative burst in neutrophils increases the rate of release of reactive oxygen
species and that these are, in turn, neutralized by high plasma ascorbate levels.
Enhancing intrinsic antioxidant defense by increasing exogenous antioxidant intake
is thus theorized to be of long-term benefit to serious endurance athletes engaged
in heavy training and competition.
Keywords
Upper respiratory tract infections - exercise - neutrophil function - antioxidant
supplementation - vitamin C
