Vitamin C, neutrophil function, and upper respiratory tract infection risk in distance runners: the missing link

Moderate submaximal exercise results in neutrophilia and enhanced phagocytic and oxidative capacity of neutrophils. It has been hypothesized, however, that during intensive exercise and periods of intensive training this pro-oxidative effect becomes suppressive. Vitamin C is widely recognized for its antioxidant function in extracellular fluid, and it has been shown to neutralize O2-, HOCl, and .OH and to attenuate the suppression of phagocytic function. Clinical manifestation of reduced neutrophil function following participation in ultramarathon races has, however, not been observed. Although neutrophils constitute 50-60% of leukocytes and although they are the first line of defense to bacteriological invasion, postrace episodes of upper respiratory tract infection (URTI) are not correlated with a decrement in the function of this individual parameter of immune function. The efficacy of Vitamin C supplements in reducing the incidence of postrace URTI symptoms, therefore, cannot be fully explained at this stage.