Handbook of Vitamin C Research

Impact of Vitamin C on Exercise-Induced Oxidative Stress 27reporting null findings, supplementation has typically not resulted in detrimental outcomes,with the exception of a few studies reporting an exacerbation in oxidative stress and tissueinjury following antioxidant treatment. These results are likely due to variability in terms ofcirculating transition metals (especially following muscle damaging exercise) and vitamin Cpresent within the subject population.Recall from above that the combination of excessive levels of catalytic metals (secondaryto muscle damaging exercise) coupled with low dose vitamin C would be expected to resultin the greatest chance of observing a prooxidant effect of supplementation. Althoughattenuation in oxidative stress has commonly been observed, whether or not this isrepresentative of a beneficial outcome remains a topic of debate for several reasons. To thisour knowledge, only one study exists reporting an ergogenic benefit of vitamin Csupplementation [159]. In fact, a decrease in performance as been reported by someinvestigators following supplementation [165,166]. Moreover, exercise-induced RONS havebeen suggested to serve as the necessary ―signal‖ responsible for driving several beneficialadaptations to exercise, thus attenuation of this signal may actually blunt this response. Atransient elevation in various biomarkers of oxidative stress may simply be a secondaryconsequence to the activation of this signal and thus may not hold any clinical relevance.This issue is discussed in greater detail in a later section. Clearly more research is neededwithin the area prior to the establishment of firm guidelines related to when supplementationis or is not warranted in relation to exercise. The next section will address the effects ofvitamin C on anaerobic exercise-induced stress.Anaerobic Exercise: Human StudiesIn opposition to aerobic exercise-induced RONS production, which is chiefly derivedfrom accelerated mitochondrial superoxide production secondary to increased oxygenconsumption, RONS produced during anaerobic work bouts are primarily produced byvarious radical generating enzymes (e.g., XO, NADPH oxidase) in response to conditions ofischemia followed by reperfusion. Recall from above that these RONS have been suggestedto interfere with force production capabilities during the bout itself, as well as exacerbatedmuscle damage following exercise, in turn potentially serving to impair performance and/orprolong the recovery process. Thus, the use of vitamin C (either alone or in combination) hasbeen utilized by several investigators in an effort to blunt both the primary production ofRONS via XO and NADPH oxidase, as well as the secondary formation of RONS viarespiratory burst and subsequent muscle injury. These studies are discussed below, separatedby those that administered vitamin C ether independently or in conjunction with otherantioxidant agents.Vitamin C AloneThe first study to investigate the effects of independent administration of vitamin C inrelation to anaerobic exercise-induced muscle damage was conducted by Kaminski et al.,