Handbook of Vitamin C Research

Impact of Vitamin C on Exercise-Induced Oxidative Stress 25(supplied via supplementation) serves to spare the use of the enzymatic components of theantioxidant defense system, in turn increasing their activity in times of oxidative stress.Concentric, Long Duration ProtocolsIn relation to long duration exercise, Sureda et al. [147] recently reported an attenuationin MDA, as well as a post exercise increase in antioxidant enzyme activity (GPx, CAT),following low dose supplementation with vitamin C (152mg) and vitamin E (50mg) for 30days prior to a half-marathon. In support of these findings, a post exercise increase in GPxand SOD, coupled with a reduction in CK has been reported in response to a duathlonperformed following 4 weeks of overtraining during which subjects were supplemented withselenium (150μg), vitamin C (120mg) and vitamin E (20mg) [148]. Davison et al., [149]reported a post exercise (2.5 hour cycle ride at 60% VO 2max ) reduction in TBARS, despite noeffects on F 2 -isoprostanes following supplementation with vitamin C and vitamin E (1000mgvitamin C + 400IU vitamin E/day for 28 days). In opposition to the above investigationsreporting significant treatment effects, two other studies have reported no effects ofsupplementation on lipid peroxidation (MDA, TBARS) [150,151], glutathione oxidation ormuscle injury (CK, MYO) [150,151], despite the use of a comparable exercise stimuli(duathlon and a 21km run).With respect to more strenuous protocols, Rokitzki and colleagues [152] reported anattenuation in CK in response to a marathon race following supplementation with 200mg ofvitamin C and 400IU of vitamin E/day for 32 days prior to the race, despite no effects onLDH or lipid peroxidation (TBARS). In direct opposition, Machefer et al. [153] reported noeffects of supplementation (150mg vitamin C + 24mg vitamin E + 4.8mg beta-carotene/dayfor 21 days) on various markers of muscle damage (CK, LDH), despite a significantreduction in TBARS following a six day ultramarathon race. No effect of a vitamin C andvitamin E mixture (1000mg vitamin C + 300IU vitamin E/day for 6 weeks) on variousmarkers of muscle damage (CK, LDH, muscle function) following an ultramarathon has alsobeen reported [154].Based on the results above, it would appear that chronic supplementation with anantioxidant mixture containing vitamin C has the potential to attenuate markers of muscledamage and oxidative stress, perhaps by way of an up-regulation in antioxidant enzymeactivity. However, as the duration of exercise is increased (above a currently undefinedlevel), RONS production likely becomes so great that the capabilities of the antioxidantdefense system become overwhelmed, effectively masking any potential benefit ofsupplementation. Perhaps more importantly, while some studies have reported an attenuationin oxidative stress/muscle injury with supplementation, the majority of studies have reportedno effects of such attenuation on exercise performance [149,151-158], with one exception[159], thus adding controversy related to the efficacy of vitamin C supplementationpertaining to exercise.