Effect of vitamin C supplementation on post-exercise recovery: A systematic review and meta-analysis of randomized double-blind placebo trials.

INTRODUCTION

Exercise-induced oxidative stress and inflammation may impair recovery and performance. Vitamin C, a potent antioxidant, has been proposed to attenuate exercise-induced muscle damage and modulate inflammatory and oxidative biomarkers during recovery.

METHODS

A systematic review and meta-analysis were conducted in accordance with PRISMA guidelines and registered in PROSPERO (CRD42024594742). Twelve randomized controlled trials involving adult participants exposed to different exercise protocols were included. Vitamin C supplementation, administered in various forms, was compared with placebo. Primary outcomes were inflammatory (CRP, IL-6) and oxidative stress (MDA) biomarkers. Risk of bias was assessed using the RoB 2.0 tool, and certainty of evidence was evaluated using the GRADE framework.

RESULTS

Pooled analyses showed no significant effects of vitamin C supplementation on IL-6 (MD = 0.00; 95 % CI: -0.25 to 0.25; p = 1.00; 2 trials, n = 31) or MDA (MD = -0.59; 95 % CI: -1.99 to 0.81; p = 0.41; 3 trials, n = 41). A significant reduction was observed for CRP (MD = -0.44; 95 % CI: -0.66 to -0.22; p = 0.0001; 2 trials, n = 52). Heterogeneity was substantial for MDA (I2 = 80 %) but negligible for IL-6 and CRP (I2 = 0 %). Risk of bias was predominantly rated as "some concerns" or "high." According to GRADE, the certainty of evidence was low for IL-6 and CRP and very low for MDA due to risk of bias and imprecision.

CONCLUSION

Based on a very limited number of small randomized trials, vitamin C supplementation does not appear to consistently modify post-exercise inflammatory or oxidative stress biomarkers. However, the available evidence is characterized by low to very low certainty, substantial methodological limitations, and imprecision. Therefore, these findings should be interpreted with caution and considered hypothesis-generating, underscoring the need for larger, high-quality, well-controlled trials.