Check out this answer from Consensus:

While vitamin C supplementation can reduce oxidative stress and muscle damage markers, it does not appear to enhance athletic performance or muscle recovery significantly. High doses may even impair beneficial training adaptations. Athletes are better advised to obtain vitamin C through a nutrient-rich diet rather than relying on supplements.

Vitamin C supplementation is commonly used by athletes with the belief that it can enhance athletic performance by reducing oxidative stress and muscle damage. However, the scientific evidence on its effectiveness is mixed, with studies showing varying results.

Key Insights

• Reduction in Muscle Damage and Oxidative Stress:

  • Some studies indicate that vitamin C supplementation can reduce markers of muscle damage and oxidative stress after intense exercise, such as lipid peroxidation and interleukin-6 levels1 2 6 7 8.

• No Improvement in Performance:

  • Despite reductions in oxidative stress and muscle damage, most studies found no significant improvement in physical performance, muscle strength, or perceived muscle soreness with vitamin C supplementation1 2 4 6 7 9.

• Potential Negative Effects on Training Adaptations:

  • High doses of vitamin C (>1 g/day) may impair training adaptations by reducing mitochondrial biogenesis and the expression of key transcription factors involved in endurance capacity4 5 10.

• Suboptimal Vitamin C Status:

  • Athletes with a suboptimal vitamin C status may experience impaired working capacity, which can be normalized by restoring vitamin C levels through diet rather than supplements3.

• Combined Supplementation with Vitamin E:

  • Combined supplementation of vitamins C and E can attenuate oxidative stress and inflammation but does not enhance performance or muscle recovery significantly2 6 7 9.