N-acetylcysteine Supplementation in Individuals With Low Glutathione Levels: the Effects on Physical Performance and Redox Homeostasis

The main objective of the present study was to investigate whether N-acetylcysteine supplementation in individuals with low glutathione levels would confer ergogenic effects by replenishing glutathione levels and by reducing oxidative stress. Towards this aim, investigators sought to exploit the large inter-individual variability in redox biomarker levels. More specifically, investigators screened 100 male participants for glutathione baseline levels in blood and formed three stratified groups according to this value (i.e., low, moderate and high; 12 individuals per group). After by-passing the regression to the mean artefact by performing a second glutathione measurement in the three aforementioned groups, investigators assessed both aerobic and anaerobic physical performance in order to acquire a more comprehensive view about the ergogenic effectiveness of the antioxidant treatment. This was accomplished by implementing three different whole-body physical performance tests (i.e., VO2max test, time trial and Wingate), as opposed to most in vivo studies that either applied isolated body-part exercise tests (e.g., by isokinetic dynamometry) or performed a single exercise test (e.g., time-to-fatigue test). It was hypothesised, that data of the present investigation will bridge the chasm between the scientific (i.e., chronic antioxidant supplementation blunts exercise performance and adaptations) and the community-based (i.e., free radicals should anyway be counteracted by "protective" exogenous antioxidants) truths about the role of antioxidants as ergogenic aids. It was also hypothesised that the results will show that low glutathione levels are linked to decreased aerobic and anaerobic physical performance accompanied by increased levels of oxidative stress and that N-acetylcysteine supplementation will restore both performance and redox homeostasis. Based on the findings of the present investigation, the widespread routine practice of consuming antioxidants during exercise training could be changed and the consumption of antioxidants would be restricted only for those who are deficient in glutathione.