Effects of nutritional supplements on the immune function of athletes

Prolonged exercise has been associated with depressed immune function, and hence an increased risk of infection. However, several nutritional supplements may reduce or overcome this problem. Thus, the aims of this thesis were to investigate the effects of some nutritional supplements on athletes immune function. In study 1 (Chapter 3), effects of several vaccine stimulant dose on whole blood culture cytokine production was carried out to determine effective vaccine stimulant dose; which was found to be between a dilution of 4000 (dose 4) and 1000 (dose 6) of the original vaccine. This finding was used for the other studies (Chapter 4 and 5). In addition, the relationship between data obtained from Evidence Investigator analyser and enzyme linked-immuno-sorbent assay (ELISA) for IL-10 was analysed and the results show a positive strong correlation between them. In study 2 (Chapter 4), in vitro effects of various immunomodulatory nutritional compounds on antigen-stimulated whole blood culture cytokine production was investigated and it was found that caffeine and quercetin showed tendency towards decrease cytokine production as the doses were increased. On the other hand, an upward trend was evident with kaloba, where high dose of kaloba seemed to increase the cytokine production. Since kaloba appeared to act as an immunostimulant in vitro, its effects on the immune response to prolonged exercise were examined in study 3 (Chapter 5). However, 7 days kaloba supplementation (20 mg of the root extract) did not alter athletes immune response although prolonged moderate intensity exercise significantly decreased S-IgA secretion rate and concentration post-exercise with the values returning to baseline by 1 h post-exercise. A 14-strain probiotic supplement effects on salivary antimicrobial proteins at rest and in response to an acute bout of prolonged exercise was investigated in study 4 (Chapter 6). Unfortunately, 30 days supplementation of the 14-strain probiotic appeared not enough to induce any significant effects on salivary antimicrobial proteins. Lastly, in study 5 (Chapter 7), the effects of a Lactobacillus probiotic on healthy people, who tend to have a higher than normal incidence of infection due to exercise stress-induced immune impairment was studied. In summary, this 16-week intervention study on 267 athletes found that regular ingestion of the probiotic reduced the extent to which training was negatively affected in endurance athletes when infection was present, and increased both S-IgA concentration and secretion rate over time. But it did not appear to reduce URTI incidence or the duration and severity of URTI episodes. Two major confounding factors, namely the unexpectedly low incidence of URTI during the winter period and the lower baseline S-IgA in the probiotic group may have prevented potential beneficial effects of probiotic supplementation from being identified.