INTRODUCTION: Elite athletes are exposed to physiological and psychological stressors that may impair immunity and increase the risk of upper respiratory (URS) and gastrointestinal symptoms (GIS). Gut microbes have a substantial influence on systemic immune function (Roberfoid et al., 2010). Dietary prebiotic galactooligosaccharides are effective at altering the gut microbiome and have been shown to reduce URS in academically stressed students (Hughes et al., 2011). Whether prebiotics could also reduce URS and GIS in elite athletes is unclear. Therefore, the aim of this study was to investigate the effect of a 24-week prebiotic intervention on markers of immunity and URS and GIS in elite rugby union players during a regular playing season. METHODS: Thirty-three elite male rugby union players were randomised to receive 2.9 g/d of either Bimuno-galactooligosaccharide (B-GOS; n=16) or a maltodextrin placebo (PLA; n=17) for 24 weeks in a double-blind design. Daily URS and weekly GIS were self-reported using questionnaires. At baseline (B), 12 weeks (12W) and 24 weeks (24W) salivary immunoglobulin A (sIgA) and plasma C-reactive protein (CRP) and tumour necrosis factor alpha (TNF-a) were measured. RESULTS: There was no between-group difference in URS incidence or severity, but the mean duration of episodes was shorter in B-GOS (7.4 ± 2.8 days) than PLA (9.8 ± 4.1 days) (P = 0.04). Area under the curve of weekly GIS scores were lower in B-GOS (Median [IQR], 50 [10.5-139.5]) than PLA (Median [IQR], 149 [69-208]) (P = 0.03). The number of symptom free weeks for GIS was higher in B-GOS than PLA (P = 0.04). SIgA secretion rate at B and 12W was not different between-groups however, at 24W it was greater in B-GOS (Median [IQR], 142 µg/min [94.9-155.0]) than PLA (Median [IQR], 86 µg/min [71.5-105.5]) (P = 0.01). Plasma CRP and TNF-a did not differ between groups across the study (P > 0.05). CONCLUSION: Twenty-four weeks of a prebiotic B-GOS intervention reduced the duration of URS, the incidence and severity of GIS and enhanced sIgA secretory rate in elite rugby union players. These findings suggest that B-GOS has the potential to modulate immune function and reduce illness, which may improve an athlete`s availability to train and compete.
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