Antioxidants exercise and immune function
While it remains debatable as to whether athletes should take antioxidant supplements, there is some evidence for beneficial effects of high-dose vitamin C supplements (1000 mg/day) on the immune system during prolonged exercise. Fischer et al. (2004) reported that supplementation of
vitamin C (500 mg/day) and vitamin E (400 i.u./day) for 29 days blunted exercise-induced interleukin-6
(a cytokine involved in stimulating immune response) release from contracting human skeletal muscle. A further study investigated the effects of two-week supplementation with vitamin C (1000 mg/day) or a placebo on cortisol, interleukin-6 and neutrophil responses to 2.5 hours of cycling at 60%
VO2 max in nine endurance trained males. All subjects completed both trials utilising a randomized crossover design. While increases in plasma antioxidant capacity and a reduced cortisol response were reported in the vitamin C trial, measures of neutrophil function were significantly lower, suggesting that vitamin C was not effective in protecting against suppression of some aspects of immune function in trained athletes post-exercise (Davision & Gleeson 2006). Athletes may there-fore consider taking vitamin C supplements as an insurance policy in the short-term to protect against illness when dietary intake and availability of fruits and vegetables rich in vitamin C may be restricted, such as when travelling and during competitions (IOC 2010). In terms of other antioxidant potential, the role of quercetin (a plant-derived antioxidant) on the immune system has not been extensively studied. However, one study by Nieman et al; (2007) reported a lower prevalence of URTI in trained cyclists undertaking a period of intensive training – a time when athletes may be more susceptible to colds and infections. While the researchers reported a reduction in illness, no changes in markers of immune system function were observed.