The effect of 2 weeks vitamin C supplementation on immunoendocrine responses to 2.5 h cycling exercise in man

An increased systemic concentration of stress hormones (of the hypothalamic-pituitary adrenal axis) and some cytokines may contribute to the depression of immune cell function typically observed after prolonged exercise. The aim of the present study was to determine the effect of 2 weeks of supplementation with vitamin C (VC) on cortisol, adrenocorticotrophic hormone, interleukin-6, oxidative stress and neutrophil responses to a single bout of endurance exercise. Nine healthy endurance-trained males exercised for 2.5 h at 60% \(\dot{V}\hbox{O}_{2{\rm max}}\) after 2 weeks of placebo (PLA) or VC (1,000 mg day⁻¹) supplementation. All participants completed both trials utilising a randomised crossover design with a minimum 14 day washout period between trials. There was a significant trial × time interaction effect for plasma cortisol concentration (P = 0.039) which tended to be lower in the VC trial but post hoc analysis found no specific between trial differences. There was a significantly lower post-exercise neutrophilia (P < 0.014) in the VC trial, compared with the PLA trial. There was no trial × time interaction for measures of neutrophil function (bacteria-stimulated elastase release, fMLP or PMA-stimulated oxidative burst). However, there was a trend for higher fMLP-stimulated neutrophil oxidative burst in the VC compared with PLA trial (trial × time interaction, P = 0.075). These results suggest that supplementation with VC for a period of up to 2 weeks provides little to no protection against the depression of neutrophil function which typically occurs after endurance exercise.