Antioxidant use has long been incorporated into the regular routines of numerous athletes. Historically, this has been especially true for endurance athletes. Antioxidants such as vitamins A, C, and E as well as Beta Carotene have long been suggested to protect active people from oxidative tissue damage. Although most evidence suggests non-athletes consuming a balanced diet do not benefit from additional antioxidant supplementation, numerous authors have encouraged endurance athletes to take supplemental antioxidants due to the increased oxidative damage which occurs as result of sustained physical activity. However, recent evidence suggests that antioxidant supplementation during endurance activity may actually hinder athletic performance.
Let’s take a few steps back. Antioxidants are nutrients that act to prevent oxidative damage resulting from free radical formation. A free radical is a molecule that has an unpaired electron in its outer orbit making it highly reactive. They often react with a stable compound in order to pair its unpaired electron. Free radicals are believed to be produced in numerous ways. The most commonly cited mechanism of exercise related production is mitochondrial leak due to the increased oxygen flux to the mitochondria during exercise. Jenkins and Goldfarb (1993) estimated that 4-5% of the oxygen consumed in mitochondrial oxidation would eventually form oxygen species with unpaired electrons. More recent evidence suggests that other mechanisms may contribute more free radicals than mitochondrial leak including the inflammatory response, auto-oxidation of heme proteins, and ischemia-reperfusion. Regardless of how they are created, when free radicals are produced in excess, cellular damage can occur. Antioxidants can scavenge free radicals, bind metal ions to prevent them from reacting with reactive species, and even repair damage resulting from oxidation.
As previously suggested, antioxidant supplementation has become a commonplace with endurance athletes. Knez and Peake (2010) assessed the nutrition records of 37 ultraendurance triathletes for one week and found that all included subjects met or exceeded dietary reference intakes for all vitamins with the exception of Vitamin D. Over 60% of the athletes included in the study took vitamin supplements although only one athlete was recommended to do so based on formal medical advice. The most common supplements were Vitamin C (96%) and Vitamin E (80%), both antioxidants. The inherent dangers of this practice are relatively slim as most common antioxidant supplements are not toxic even at relatively high levels of supplementation. However, the overall benefits may not be all they have been purported to be and indeed may even hinder performance if taken at the wrong time.
The benefits of an antioxidant rich diet on enhancing the immune system have been well supported in literature. However, the benefits of antioxidant supplementation on performance are poorly understood. Numerous supplement companies suggest that antioxidant supplementation may possibly delay fatigue and improve endurance performance, however the scientific documentation supporting these claims have been lacking. In fact, recent evidence suggests it may be counterproductive to take antioxidants during endurance activities. Braakhuis and colleagues (2013) found that an antioxidant rich diet had no effect on performance in competitive rowers which was also the finding in Keith (2006). No evidence has been found supporting the use of vitamin E as an ergogenic aid either. According to Rokitzki et al. (1994) and Tidus et al. (1995), vitamin E supplementation had no performance effect in swimming, submaximal cycling, cycling to exhaustion, hockey, and marathon running. Furthermore, in a separate 2013 study, the Braakhuis et al. found that consuming a beverage containing vitamin C during performance actually hinders performance in female distance runners. This supported the findings by Ristow et al. (2009) who suggested high levels of vitamins E and C led to a retard of training adaptations during exercise and was further supported by Gomez-Cabrera et al. (2008) who found high levels of vitamin C decreased endurance capacity.
The fact that evidence now suggests the use of vitamin C during physical actually hindering performance may require a bit more explanation. There is a growing body of literature which supports the NEED for free radicals during exercise in order to enjoy the benefits of training adaptations. Reactive oxygen species have been shown to serve as a signal to promote the expression of skeletal muscle proteins, mitochondrial proteins, and heat shock proteins. Oral supplementation of Vitamin C has been shown to blunt the body’s natural ability to fight inflammation thus further limiting overall training adaptations. Furthermore, evidence suggests that endurance training promotes increased endogenous antioxidants in muscle fibers increasing the natural level of protection against exercise-mediated oxidative damage. Finally, it has been reported that vitamin C prevented expression of transcription factors which are involved in biogenesis which is consistent with the previous suggestions that vitamin C supplementation reduced training-induced adaptations. According to Braakhuis et al. (2013) training status appeared to have a greater impact on antioxidant mobilization after exercise than diet in elite athletes.
It is without a doubt that more research will be performed over this area in the future. Braakhuis et al. (2013) claimed to be the first to investigate the relationships between diet, exercise training, performance, and antioxidant status in elite athletes. Surely many more studies will follow. Based on the available evidence, it seems that a few conclusions can be made. First, most endurance athletes are already getting sufficient levels of most vitamins, including vitamins C and E. Endurance athletes with diets containing antioxidant levels which exceed the dietary reference intakes will not likely improve performance. However, there may be an associated reduced risk for upper respiratory tract infections as well an increased ability to sustain iron status and heme proteins through the processes noted above. A final conclusion is that consuming antioxidants during endurance exercise may have a negative effect on performance. Athletes should focus first on gaining antioxidants through a balanced diet. However the addition of low level supplemental antioxidants may still provide health benefits.
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