Vitamin C supplementation and Endurance Performance

A couple of weeks ago, I posted an article on my Twitter account regarding Vitamin C supplementation and its effect on athletic performance. An interesting question was posed on whether the supplement, if spaced out further away from the workout, would have the same effect or whether that negative effect on performance is only caused when taken prior to a workout? I thought I’d explain the mechanism discussed in the research article (can be read here) and discuss the role of Vitamin C, as well as other antioxidants, to determine if supplementation of these are even necessary. Before discussing the article, we have to give a background as to why antioxidants are important during exercise. When running (or doing any endurance exercise for that matter), fatigue will set in because of mitochondrial dysfunction and oxidative stress that occurs as our body tries to adapt to the training stimulus. Our bodies produce ROS (reactive oxidative species or free radicals) in response to exercise. ROS serves as an indicator for our body to produce more mitochondria because this is where oxidative phosphorylation (the process by which your body breaks down consumed oxygen to drive the formation of ATP) occurs. Almost 98% of the oxygen you consume goes through this process, the other 2% gets reduced into a free radical. It is estimated that for every 25 molecules of oxygen the get broken down by normal respiration, 1 free radical gets made. So as oxygen demands increase, the more free radical production is going to increase in a linear fashion creating a balance that the mitochondria can efficiently manage. The body can protect and dispose of free radicals as they are produced using specific endogenous antioxidants such as: mitochondrial superoxide dismutase, glutathione peroxidase, and glutamylcysteine synthetase. This linear balance continues until oxygen consumption exceeds 60% of its max. After this point, ROS production surpasses endogenous antioxidant defense, which can lead to cellular damage in skeletal muscle tissue as free radicals tend to target and react with proteins, nucleic acids, and lipids. This is bad right? Well, that depends. In excess, yes, free radicals are bad as they can lead to serious tissue damage and even cell death. But, free radicals have important training implications as well. When produced during exhaustive exercise, ROS acts as a signal for the body to produce more of the endogenous antioxidants above the level that is normally needed. For example, a 2006 study by Cabrera et al. showed that as the body produced levels of ROS-induced xanthanine oxidase (which can lead to tissue damage), a nuclear protein NF-kappaB was activated. This nuclear protein is one of the main constituents in the pathway the produces more mitochondria. Thus, the ROS production was signaling the body that a greater mitochondria content was needed. This signal allows the body, therefore, to adapt to an intensive training session by stimulating it to increase its amount of cellular mitochondria to handle the stress of future exercise demands. So to get back to the original question of Vitamin C supplementation, why is it bad? If antioxidants help manage the production of free radicals and signal the body that more mitochondria is needed, then supplementation must be good right? Wrong, antioxidant supplementation, specifically vitamin C in this study, do effectively block the production of free radicals. But that doesn’t mean it’s a good thing. By blocking this response, the indicator that the body is getting fatigued either doesn’t happen or becomes delayed. So endogenous antioxidants take longer to respond, meaning less mitochondria production as a result of the training stimulus. This can reduce the effect of a given workout, as the training adaptation will now take longer. So is antioxidant or vitamin C supplementation completely wrong? Not necessarily, I am obviously not suggesting that someone with low levels of endogenous antioxidants would not benefit from supplementation. But for an athlete, who consumes a normal well-balanced diet, exogenous antioxidant supplementation may not be necessary, regardless of when they are taken. Especially when you consider that the daily requirements of vitamin C are around 90 mg in the normal population and 300mg in athletes, where most supplements contain 500-1000mg and can oversaturate the blood. These daily needs are easily achieved eating normal fruits and vegetables (such as peaches, oranges, mangos, strawberries, brocoli, cauliflower, tomatoes, and lettuce).


Gomez-Cabrera MC, Domenech E, Romagnoli M, et al. (2008). Oral administration of vitamin C decreases muscle mitochondrial biogenesis and hampers training-induced adaptations in endurance performance. American Journal of Clinical Nutrition 87, 142-149.

Gomez-Cabrera MC, Domenech E, Viña J. Moderate exercise is an antioxidant: upregulation of antioxidant genes by training. Free Radic Biol Med. 2008;44:126–131.

Ristow M, Zarse K, Oberbach A, Kloting N, Birringer M, Kiehntopf M, Stumvoll M, Kahn CR, Bluher M (2009). Antioxidants prevent health-promoting effects of physical exercise in humans. Proceedings of the National Academy of Sciences of the United States of America 106, 8665-8670.

3 thoughts on “Vitamin C supplementation and Endurance Performance

  1. Thanks for answering my question regarding the timeliness of Vit C supplementation. This really makes you rethink what many have been preaching for years. As Steve Magness said in his twitter, sometimes damage is a good thing.

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