The aim of this study was to compare the redox balance in competitive adult swimmers against recreational practitioners, controlling for Mg intake. Fifteen, competitive swimmers and 16 recreational practitioners, all male and aged 18-25years, were recruited into the study. Oxidative and muscle damage markers, and antioxidant enzymes and non-enzymatic antioxidants were evaluated by photometry (except for thiobarbituric reactive substances (TBARS), which was assessed by fluorimetry). Controlling for the level of exercise, inverse correlations were observed for uric acid and glutathione reductase (GR) or susceptibility of red blood cells to peroxidation (RBCPx); plasma adrenaline oxidase activity (AdOx) and carotenoids; TBARS and GR or Vit E; and direct correlations were observed between AdOx and creatine kinase (CK) or TBARS; CK and superoxide dismutase activity; GR and RBCPx. Controlling for Mg intake in addition to exercise level revealed new inverse correlations: between carotenoids and TBARS or lactate, and new direct correlations between lactate and AdOx or TBARS; cortisol and AdOx, CK, lactate dehydrogenase, or methemoglobin reductase. The associations between uric acid and RBCPx; AdOx and CK or TBARS; and GR and RBCPx lost their significance. All others remained significant. These outcomes suggest that the coordination between antioxidant defences may be partially modulated by Mg, which may be the result of its ability to stabilize cell membranes and oxidation targets, such as adrenaline.
Keywords: antioxidants; athletes; magnesium; reactive oxygen species.