Across 3 studies, 2 reported beneficial effects (moderate to large effect sizes) on reducing oxidative stress, and 1 reported neutral findings. The median study duration was 84 days (12 weeks). The most studied dose was 1000 mg/day, and populations were primarily clinical (patients with coronary artery disease and older women with sarcopenia).
Caveats: Evidence base is small (only 3 studies) — conclusions should be considered preliminary. One beneficial study is a systematic review that included various antioxidants (primarily L-carnitine and melatonin), not exclusively vitamin C, so its contribution is indirect. The RCT combined vitamin C with vitamin E and resistance training, so effects may not be solely from vitamin C. Generalization to healthy individuals is uncertain.
While additional verification of the safety and efficacy of these supplements is still necessary, current evidence suggests that these supplements have potential applications for health promotion and disease prevention among athletes and more diverse populations.
from: Recent Progress in Applicability of Exercise Immunology and Inflammation Research to Sportnine reported on supplemental antioxidants (i.e., L-carnitine and melatonin) ... that were effective at lowering OS (P < 0.05)
the AS group had increased GSH (P < .001, d = 1.52) and GSH/GSSG ratio (P < .001, d = 1.52), and reduced GSSG (P < .001, d = 0.96) and malondialdehyde (P < .001, d = 1.65) compared to the PLA group
antioxidant defense modulators (vitamin C, sulforaphane, taheebo)