Inter‐individual variability in redox and performance responses after antioxidant supplementation: A randomized double blind crossover study

Abstract

AbstractAimWe aimed to investigate the inter‐individual variability in redox and physiological responses of antioxidant‐deficient subjects after antioxidant supplementation.MethodsTwo hundred individuals were sorted by plasma vitamin C levels. A low vitamin C group (n = 22) and a control group (n = 22) were compared in terms of oxidative stress and performance. Subsequently, the low vitamin C group received for 30 days vitamin C (1 g) or placebo, in randomized, double‐blind, crossover fashion, and the effects were examined through a mixed‐effects model, while individual responses were calculated.ResultsThe low vitamin C group exhibited lower vitamin C (−25 μmol/L; 95%CI[−31.7, −18.3];p < 0.001), higher F2‐isoprostanes (+17.1 pg/mL; 95%CI[6.5, 27.7];p = 0.002), impaired VO2max(−8.2 mL/kg/min; 95%CI[−12.8, −3.6];p < 0.001) and lower isometric peak torque (−41.5 Nm; 95%CI[−61.8, −21.2];p < 0.001) compared to the control group. Regarding antioxidant supplementation, a significant treatment effect was found in vitamin C (+11.6 μmol/L; 95%CI[6.8, 17.1],p < 0.001), F2‐isoprostanes (−13.7 pg/mL; 95%CI[−18.9, −8.4],p < 0.001), VO2max(+5.4 mL/kg/min; 95%CI[2.7, 8.2],p = 0.001) and isometric peak torque (+18.7; 95%CI[11.8, 25.7 Nm],p < 0.001). The standard deviation for individual responses (SDir) was greater than the smallest worthwhile change (SWC) for all variables indicating meaningful inter‐individual variability. When a minimal clinically important difference (MCID) was set, inter‐individual variability remained for VO2max, but not for isometric peak torque.ConclusionThe proportion of response was generally high after supplementation (82.9%–95.3%); however, a few participants did not benefit from the treatment. This underlines the potential need for personalized nutritional interventions in an exercise physiology context.