Vitamin C (L-ascorbic acid, ascorbate) is an essential nutrient for humans. It is needed for the growth and repair of tissues in all parts of your body .
Vitamin C is found in a wide variety of fruits and vegetables. Good sources include: oranges and orange juice, red and green peppers, strawberries, blackcurrants, broccoli, potatoes .
Adults on average need to supplement with 40 mg of vitamin C per day. Some bodybuilding multivitamins contain up to 1000 mg of vitamin C.
Antioxidant Activity of Vitamin C
Bodybuilders often supplement with Vitamin C because intense muscular work can result in oxidative stress. It has been generally accepted that increasing the concentrations of antioxidants within a muscle cell should provide greater protection against oxidative stress and should reduce fatigue.[3,4] However, Gomez-Cabrera and assistants  concluded in their study that administration of vitamin C significantly (P = 0.014) impaired endurance capacity probably because it prevents some cellular adaptations to exercise. They said: “We were surprised to see that vitamin C prevents these beneficial effects of training.” Reactive oxygen species formed in exercise activate mitochondrial biogenesis and the expression of antioxidant enzymes in skeletal muscle but vitamin C administration prevents the activation.
Graeme L. Close et al.  investigated the effect of ascorbic acid supplementation on muscle soreness. Muscle function was impaired post-exercise in for all subjects from downhill running, although a delayed recovery was noted in group supplemented with ascorbic acid (1 gram).
It is important to consider that free radicals are not always damaging to cells, in many cases they serve as signals in muscle cell metabolism. Antioxidant vitamins may potentially interfere with that. It was even suggested that ascorbic acid in high concentrations may act as a pro-oxidant (not proven in vivo ) as well as an antioxidant. This could be the reason for observed delayed recovery with ascorbic acid supplementation in Graeme L. Close et al. study.
Vitamin C is involved in a number of biochemical pathways that are important for the health of exercising individuals . Cortisol is steroid hormone released in response to physical or mental stress  and is also known as the archenemy of bodybuilders. Its main function is to increase blood sugar (glucogenesis) ; it counteracts insulin. Cortisol also suppresses immune system, decreases bone formation and it aids in fat, protein and carbohydrate metabolism. 
Several studies with runners competing in prolonged running have shown that ingesting vitamin C attenuated post-race serum cortisol concentration [14-16]. However, carbohydrate intake in these subjects was not controlled and they were not randomized to treatment groups. Carbohydrate ingestion during prolonged and intense exercise is associated with higher plasma glucose levels and attenuated cortisol response [17,18].
David C. Nieman and others  wanted to improve previous studies with randomizing subject into treatment groups and by carefully measuring carbohydrate intake. The results of this study considerably different from the previous studies. Plasma ascorbic acid was significantly higher (and rose more during the race) in the vitamin C compared with placebo. Serum cortisol was strongly elevated in both groups but surprisingly significantly greater elevation was measured in the vitamin c group.
Several explanations are possible. In previous studies subjects were not randomized to treatment groups and carbohydrate intake during race were ad libitum and retrospectively estimated.
Basically, the only evidence suggesting that vitamin C is a powerful antioxidant in biological systems is from in vitro studies. Its beneficial antioxidant role in humans has not been supported by currently available clinical studies. Other than preventing scurvy, vitamin C has no proven benefits. 
Effects on Cholesterol and Triglycerides
Meta-analysis  which evaluated thirteen randomized controlled trials published between 1970 and June 2007 reported that supplementation with at least 500 mg/d of vitamin C, for a minimum of 4 weeks, can result in a significant decrease in serum LDL cholesterol and triglyceride concentrations. However, observed effects are modest but when it comes to the incidence of coronary heart disease any change can be beneficial, especially since ascorbic acid is low cost and is non-toxic. Limitation of this review is a high diversity of studies included; e.g. subject age varied between 48 and 82 years (vitamin C concentration in serum decreases with aging, whereas a concomitant increase in total serum concentration occurs).
Vitamin C has also been shown to protect HDL cholesterol from lipid oxidation .
Too little vitamin C can lead to anemia, bleeding gums, decreased ability to fight infection, decreased wound-healing rate, easy bruising, gingivitis, possible weight gain because of slowed metabolism and many more . Clinical expression of vitamin C deficiency, scurvy, is a lethal condition unless appropriately treated .
Side Effects and Dosage
Higher doses of vitamin C (more than 1000 mg) can cause stomach pain, diarrhoea, flatulence. Doses up to 1000 mg are unlikely to cause any harm. These symptoms should disappear once you stop taking vitamin C supplements. However, serious side effects are very rare as body can not store vitamin C .
- “Vitamin C”. Food Standards Agency (UK). Retrieved 1. Mar 2013.
- Gomez-Cabrera, Mari-Carmen, et al. “Oral administration of vita C decreases muscle mitochondrial biogenesis and hampers training-induced adaptations in endurance performance.” The American journal of clinical nutrition 87.1 (2008): 142-149.
Konig, D., et al. “Exercise and oxidative stress: significance of antioxidants with reference to inflammatory, muscular, and systemic stress.” Exercise Immunology Review 7 (2001): 108-133.
- Jackson, M. J. “Muscle damage during exercise: possible role of free radicals and protective effect of vitamin E.” Proceedings of the Nutrition Society 46.01 (1987): 77-80.
Close, Graeme L., et al. “Ascorbic acid supplementation does not attenuate post-exercise muscle soreness following muscle-damaging exercise but may delay the recovery process.” British Journal of Nutrition 95.5 (2006): 976-981.
Carr, Anitra, and Balz Frei. “Does vit C act as a pro-oxidant under physiological conditions?.” The FASEB journal 13.9 (1999): 1007-1024.
Podmore, Ian D., et al. “VitaC exhibits pro-oxidant properties.” Nature 392.6676 (1998): 559-559.
- Peake, Jonathan M. “Vitamin C: effects of exercise and requirements with training.” International journal of sport nutrition and exercise metabolism 13.2 (2003): 125.
- Rosmond, Roland, Mary F. Dallman, and Per Björntorp. “Stress-related cortisol secretion in men: relationships with abdominal obesity and endocrine, metabolic and hemodynamic abnormalities.” Journal of Clinical Endocrinology & Metabolism 83.6 (1998): 1853-1859.
- Marieb, Elaine Nicpon, and Katja Hoehn. Human anatomy & physiology. Pearson Education, 2007.
- National Institutes of Health. Retrieved from http://www.nlm.nih.gov/ at 28. May 2013
- McRae, Marc P. “VitC supplementation lowers serum low-density lipoprotein cholesterol and triglycerides: a meta-analysis of 13 randomized controlled trials.” Journal of chiropractic medicine 7.2 (2008): 48-58.
- Hillstrom, Robert J., Angela K. Yacapin-Ammons, and Sean M. Lynch. “Vitamin C inhibits lipid oxidation in human HDL.” The Journal of nutrition 133.10 (2003): 3047-3051.
- Nieman, David C., et al. “Influence of vitamin C supplementation on cytokine changes following an ultramarathon.” Journal of Interferon & Cytokine Research 20.11 (2000): 1029-1035.
- Peters, E. M., et al. “Vitamin C supplementation attenuates the increases in circulating cortisol, adrenaline and anti-inflammatory polypeptides following ultramarathon running.” International journal of sports medicine 22.7 (2001): 537-543.
Peters, E. M., R. Anderson, and A. J. Theron. “Attenuation of increase in circulating cortisol and enhancement of the acute phase protein response in vitamin C-supplemented ultramarathoners.” International journal of sports medicine 22.02 (2001): 120-126.
Nieman, David C., et al. “Cytokine changes after a marathon race.” Journal of Applied Physiology 91.1 (2001): 109-114.
Nieman, David C., et al. “Influence of mode and carbohydrate on the cytokine response to heavy exertion.” Medicine and science in sports and exercise 30.5 (1998): 671.
Nieman, David C., et al. “Influence of vitamin C supplementation on oxidative and immune changes after an ultramarathon.” Journal of Applied Physiology 92.5 (2002): 1970-1977.
- Padayatty, Sebastian J., et al. “Vitamin C as an antioxidant: evaluation of its role in disease prevention.” Journal of the American college of Nutrition 22.1 (2003): 18-35.