Here is a good study to partially answer your question. Just don't take it right before a workout as I have read that vitamin C andcan increase oxidative damage during resistance training.
Vitamin C Supplementation Attenuates the Increases in Circulating Cortisol, and Anti-Inflammatory Polypeptides Following Ultramarathon Running
E. M. Peters1, R. Anderson2, D. C. Nieman3, H. Fickl2, V. Jogessar4
1Department of Physiology, Faculty of Medicine, University of Natal, Durban, South Africa
2Medical Research Council Unit for Inflammation and Immunity, Department of Immunology, Institute for Pathology, University of Pretoria, South Africa
3Department of Health and Exercise Sciences, Appalachian State University, Boone, USA
4Department of Haematology, Faculty of Medicine, University of Natal, Durban, South Africa
The effects of vitamin C supplementation on the alterations in the circulating concentrations of cortisol, , interleukin-10 (IL-10) and interleukin-1 receptor antagonist (IL-1Ra) which accompany ultramarathon running were measured using immuno-chemiluminescence, radioimmunoassay and ELISA procedures. Forty-five participants in the 1999 Comrades 90 km marathon were divided into equal groups (n = 15) receiving 500 mg/day Vit C (VC-500), 1500 mg/day Vit C (VC-1500) or placebo (P) for 7 days before the race, on the day of the race, and for 2 days following completion. Runners recorded dietary intake before, during and after the race and provided 35 ml blood samples 15 - 18 hrs before the race, immediately post-race, 24 hrs post race and 48 hrs post-race. Twenty-nine runners (VC-1500, n = 12; VC-500, n = 10; P, n = 7) complied with all study requirements. All post-race concentrations were adjusted for plasma volume changes. Analyses of dietary intakes and blood glucose and anti-oxidant status on the day preceding the race and the day of the race did not reveal that carbohydrate intake or plasma vitamins E and A were significant confounders in the study. Mean pre-race concentrations of serum vitamin C in VC-500 and VC-1500 groups (128 ± 31 and 153 ± 34 μmol/l) were significantly higher than in the P group (83 ± 39 μmol/l). Immediate post-race serum cortisol was significantly lower in the VC-1500 group (p < 0.05) than in P and VC-500 groups. When the data from VC-500 and P groups was combined (n = 17), immediate post-race plasma adrenaline, IL-10 and IL-1Ra concentrations were also significantly lower (p < 0.05) in the VC-1500 group. The study demonstrates an attenuation, albeit transient, of both the adrenal stress hormone and anti-inflammatory polypeptide response to prolonged exercise in runners who supplemented with 1500 mg vitamin C per day when compared to ≤ 500 mg per day.