Dr. Dwayne Jackson

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Vitamin C

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Vitamin C


Also known as ascorbic acid or ascorbate, vitamin C is a water-soluble vitamin that is not synthesized or stored in the body in high amounts. Its main role is to provide potent antioxidant protection to cells and systems in the body. As such, vitamin C is involved in immune system protection, wound healing, and synthesizing collagen, amino acids, hormones, and neurotransmitters.



It is essential to get adequate amounts of vitamin C in the diet because, unlike many other mammals, humans cannot synthesize this valuable micronutrient. Although vitamin C is found in abundance in most citrus fruits and in many vegetables (like peppers, broccoli, and cabbage), a study published in the International Journal of Sport Nutrition and Exercise Metabolism illustrates that athletes undergoing regular strenuous exercise encounter greater levels of oxidative stress —suggesting a need for supplemental antioxidant support. Furthermore, dieting strength athletes with heavy training schedules (like bodybuilders) who follow low carbohydrate diets (with little variety) tend to have lower vitamin C intake.


Although recent research has shown that long-term “mega-dosing” of vitamin C can negatively impact muscular gains and performance, there is an abundance of data illustrating that modest dosing (500mg to 1g per day) can produce significant ergogenic effects. Below we have summarized the most recent data in support of modest vitamin C supplementation.


Muscle blood flow and exercise enhancer?


It has been known for years that vitamin C’s antioxidant effects protect blood vessels from oxidative stress. During exercise, endothelial cells that line blood vessels produce vasodilators that increase blood flow to working muscle, which serves to deliver oxygen and nutrients and take away metabolic byproducts. One such vasodilator is nitric oxide (NO). Research from human and animal studies suggest that vitamin C supplementation plays a dual role in supporting increased NO-mediated vasodilation during exercise. First, vitamin C helps with NO production by protecting the rate-limiting enzyme that synthesizes NO [endothelial NO synthase (eNOS)] from free radicals that build up during exercise. Second, vitamin C increases NO bioavailability. This is supported by a study from Athens University Medical School in Greece, which showed that vitamin C taken with L-arginine boosts NO levels better than taking arginine alone. The scientists concluded that vitamin C’s antioxidant effects increase NO bioavailability by preventing its breakdown by free radicals. Due to its effects on NO (and muscle blood flow), you will find vitamin C in many of today’s pre-workout formulas.

Beyond helping to increase blood flow, vitamin C supplementation can increase exercise performance by altering feelings of fatigue. In a recent study published in Nutrition it was reported that overweight subjects undergoing a 4 week calorie restricted diet who took 500mg of Vitamin C daily had decreased signs of fatigue, heart rate, and perceived exertion during treadmill exercise.


A fat loss catalyst?


In 2007, a study published in The Journal of Nutrition reported that blood levels of vitamin C were inversely related to body mass index, body fat percentage, and waist circumferences in men and women— suggesting that low vitamin C levels may contribute to body fatness. This may be (at least partly) true because vitamin C is used by the body to synthesize carnitine—a substance required for fat burning.

Support for vitamin C as a fat burning catalyst comes from a study published in Nutrition & Metabolism, which showed that levels of vitamin C in the body correlated fat oxidation during fat burning cardio exercise on a treadmill. In this investigation fat burning was measured in subjects with marginal and adequate vitamin C levels during 60 minutes of low intensity cardio. Subsequently, subjects with marginal Vitamin C levels completed an 8-week double blind, placebo controlled vitamin C depletion-repletion trial with low intensity treadmill exercise testing. In the end, it was found that individuals with marginal vitamin C levels burned 25% less fat during the exercise compared to subjects with adequate vitamin C levels. Furthermore, vitamin C repletion (500 mg/day) in depleted subjects increased fat burning 4-fold compared to depleted control subjects.


A cure for the common cold?


Vitamin C is frequently taken as a home remedy for preventing and treating the common cold. Unfortunately the body of research on vitamin C doesn’t support it as a cure— at least for the general population. A recent Meta analysis published in The Chochrane Database of Systematic Reviews reported that although routine vitamin C dosing does not reduce the incidence of colds in the general population, it might reduce their severity and duration. Most importantly, the authors highlighted that vitamin C supplements seem to be most useful to those who are exposed to regular intense exercise. All in all, the data suggest that regular vitamin C supplementation will keep you out of the doctor’s office and in the gym.


Dosing: Finding the “sweet spot”


We hope that we have convinced you that vitamin C is an essential component of the diet, which can help you achieve your workout goals while keeping you healthy and free from sniffles. However, it must be stressed that recent evidence has shown that reactive oxygen species may mediate beneficial training adaptations and doses of vitamin C above 1g per day have been shown to impair sport/exercise performance.


So where is the “sweet spot” for vitamin C dosing? 


Well, according to the research, the beneficial effects of vitamin C come from doses ranging from 500mg to 1g per day. Based on this, on regular and non-training days, we recommend taking 500mg of vitamin C per day, split into 2 doses and taken with food. During high intensity training periods you can bump your dose up to 1 gram per day, split in 3 doses and taken with food.  This dosing regimen will ensure you have an adequate vitamin C status without the downfalls of mega-dosing.



Teixeira V1, Valente H, Casal S, Marques F, Moreira P. Antioxidant status, oxidative stress, and damage in elite trained kayakers and canoeists and sedentary controls. Int J Sport Nutr Exerc Metab. 2009 Oct;19(5):443-56.

Johnston CS1, Corte C, Swan PD. Marginal vitamin C status is associated with reduced fat oxidation during submaximal exercise in young adults. Nutr Metab (Lond). 2006 Aug 31;3:35.

Johnston CS, Beezhold BL, Mostow B, Swan PD. Plasma vitamin C is inversely related to body mass index and waist circumference but not to plasma adiponectin in nonsmoking adults. J Nutr. 2007 Jul;137(7):1757-62.

Huck CJ1, Johnston CS, Beezhold BL, Swan PD. Vitamin C status and perception of effort during exercise in obese adults adhering to a calorie-reduced diet. Nutrition. 2013 Jan;29(1):42-5. doi: 10.1016/j.nut.2012.01.021. Epub 2012 Jun 5.

Hemilä H1, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2013 Jan 31;1:CD000980. doi: 10.1002/14651858.CD000980.pub4.

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