Overview

• Free radicals are unstable, potentially harmful chemical substances which form during normal metabolism and via exposure to external factors such as pollution. Free radicals have been linked to cell membrane damage and deterioration of immune function.
• Sudden increases in training stress lead to temporary increases in production of free oxygen radicals.
• Supplementation with antioxidant vitamins may help to reduce oxidative damage until the body’s own antioxidant system can adapt to the new challenge.
• There is no consistent evidence of performance enhancement following antioxidant supplementation. Thus benefits, if any, may be subtle and short-lived.
• Regular training promotes an increase in the body’s own antioxidant defence system against free-radical damage.

Supplement Products and Protocols

• Typical anti-oxidant protocol = daily dose of 500 mg vitamin C and 500 IU vitamin E.
• Other commercial anti-oxidant supplements may also include coenzyme Q10 (ubiquinone), carotenoids (mainly B-carotene or vitamin A), and polyphenols (e.g. flavonoids).
• Antioxidants are often added to many commercial foods to extend their shelf life. Antioxidants may be added to sports supplements such as sports bars and gels to create a marketing edge as well as extend shelf life.
• Antioxidants are mainly found in plant-based foods including dark coloured vegetables, citrus fruit, legumes, nuts, grains, seeds and oils. Tea (black and green) is a rich source of flavonoids.

Situations for Use in Sport

• Athletes beginning a new period of high volume and/or high intensity training
• Athletes moving to hot environments or undertaking heat acclimatisation
• Athletes moving to altitude or undertaking altitude training

Note: While studies do not provide evidence of substantial benefits or performance enhancements following antioxidant supplementation, there is logic to support a phase of supplementation at the commencement of a period of increased training stress. Supplementation of 1-2 weeks can be justified. However, long-term/continued supplementation protocols are not warranted, nor are doses higher than those currently recommended. As such, priority must be given to a meal plan that emphasises the intake of foods naturally rich in antioxidants such as fruit, vegetables and wholegrains. This recognizes that food contains a wider spectrum of antioxidant nutrients than any commercially available supplement, and that these are likely to act in synergy with other antioxidants and nutrients.   

Concerns Associated with Supplement Use

• Antioxidant systems are complex. There is potential for antioxidant supplements to behave as pro-oxidants, if taken in excess or in ways that unbalance the anti-oxidant network.  For example, chronic supplementation with vitamin E (800 IU per day for 2 months) in combination Ironman training was shown to increase oxidative stress/damage and the inflammatory response to prolonged exercise (Nieman et al. 2004).
• If adaptations to a training stimulus or other desirable physiological processes are achieved through pathways involving oxidative processes (i.e. free radical production), antioxidant supplementation may reduce the effectiveness of the response. There is preliminary evidence of this: previously untrained subjects who supplemented with vitamin C (1000 mg per day) while completing an 8 week training program showed a reduced improvement in aerobic capacity compared with a control group.  This was attributed to a blunting of the cellular signalling pathways stimulated by training to increase oxidative capacity (Gomez-Cabrera et al. 2008).
• There is a potential for vitamin C to interact with iron. This may lead to increased absorption of iron in those susceptible to iron overload (e.g. haemochomatosis)
• High doses of vitamin C can also reduce the effectiveness of the contraceptive pill.

Further Reading

Gomez-Cabrera MC, Domenech E, Romagnoli M, Arduini A, Borras C, Pallardo FV, Sastre J, Vina J. Oral administration of vitamin C decreases muscle mitochondrial biogenesis and hampers training-induced adaptations in endurance performance. Am J Clin Nutr 2008; 87: 142-149.

Nieman DC, Henson DA, McAnulty SR, McAnulty LS, Morrow JD, Ahmed A, Heward CB. Vitamin E and immunity after the Kona Triathlon World Championship. Med Sci Sports Exerc 2004; 36: 1328-1335.

Please refer to summary table on research conducted on antioxidants.

Last updated August 2009.

This fact sheet was prepared by AIS Sports Nutrition as part of the AIS Sports Supplement Program.  The AIS Sports Supplement Program has been designed for the specific needs of AIS athletes and all attempts are made to stay abreast of scientific knowledge and of WADA issues related to anti-doping.  It is recommended that other athletes and groups should seek independent advice before using any supplement, and that all athletes consult the WADA List of Prohibited Substances and Methods before making decisions about the use of supplement products. © Australian Sports Commission 2009