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

Aim

We aimed to investigate the inter-individual variability in redox and physiological responses of antioxidant-deficient subjects after antioxidant supplementation.

Methods

Two 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.

Results

The 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%CI6.5, 27.7]; p = 0.002), impaired VO_2max (?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%CI6.8, 17.1], p < 0.001), F₂-isoprostanes (?13.7 pg/mL; 95%CI?18.9, ?8.4], p < 0.001), VO_2max (+5.4 mL/kg/min; 95%CI2.7, 8.2], p = 0.001) and isometric peak torque (+18.7; 95%CI11.8, 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 VO_2max, but not for isometric peak torque.

Conclusion

The 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.