Purpose: Prolonged physical exertion and environmental heat stress may elicit postexercise depression of immune cell function, increasing upper respiratory tract infection (URTI) susceptibility. We investigated the effects of acute and short-term vitamin C (VC) compared with placebo (PL) supplementation on URTI susceptibility, salivary immunoglobulin A (s-IgA), and cortisol responses in healthy individuals following prolonged exercise-heat stress.
Methods: Twelve participants were randomized into the VC or PL group in a double-blind design. For 12 days, participants consumed 3x500 mg tablets of VC or PL per day, with testing completed at baseline, then following acute (1 d) and short-term (8 d) supplementation. Participants performed 120.1+/-49.6 min of cycling at 54+/-6% VO2max in a hot (34.8+/-1.0 degrees C and 13+/-3% relative humidity) environment, with saliva samples collected at pre-, post-, and 72 h postexercise. Health logs specifying URTI symptoms were completed for 7 days postexercise.
Results: A 2x3x3 mixed ANOVA with a post hoc Bonferroni correction factor revealed a significant linear trend in postexercise cortisol attenuation in the VC group, 21.7+/-15.1 nmol/L (mean+/-SD) at baseline, to 13.5+/-10.0 at acute, to 7.6+/-4.2 after short term (P=.032). No differences were detected in ratio of s-IgA to protein or URTI symptoms between groups.
Conclusions: These data suggest that vitamin C supplementation can decrease postexercise cortisol in individuals performing exercise similar to that of a half-marathon or marathon in hot conditions. However, no changes in s-IgA and URTI were evident, possibly due to previous moderate training and reduced physical and psychological stress compared with athletes participating in ultramarathons.