Does the temperature of water ingested during exertional-heat stress influence gastrointestinal injury, symptoms, and systemic inflammatory profile?

OBJECTIVES: The study aimed to determine the effects of temperature of ingested water during exertional-heat stress on gastrointestinal injury, symptoms and systemic inflammatory responses. DESIGN: Randomised cross-over study. METHODS: Twelve endurance runners completed 2h running at 60% v˙O2max in 35°C ambient temperature on three separate occasions, consuming 250±40mL water before and every 15min during running at either 0.4±0.4°C (COLD), 7.3±0.8°C (COOL), or 22.1±1.2°C (TEMP). Rectal temperature and gastrointestinal symptoms were recorded every 10min during exercise. Blood was collected pre, immediately and 1h post-exercise to determine plasma intestinal fatty-acid binding protein (I-FABP), cortisol, and inflammatory cytokine concentrations. RESULTS: Compared to TEMP, COLD and COOL blunted the rise in rectal temperature (2.0±0.5°C vs. 1.6±0.4°C and 1.7±0.4°C, respectively; trial×time, p=0.033). I-FABP increased post-exercise (419%, p<0.001), with a trend for reduced I-FABP on COLD and COOL (mean reduction 460pgmL-1 and 430pgmL-1, respectively), compared to TEMP (p=0.066). No differences were observed between trials for gastrointestinal symptoms, albeit a trend for increased upper-gastrointestinal symptoms on TEMP (p=0.087) compared to COLD and COOL was observed. IL-6, IL-1β, IL-8, IL-10 and IL-1ra increased post-exercise (p<0.05); however no differences were observed between trials. CONCLUSIONS: COLD and COOL water ingestion during exertional-heat stress ameliorates thermoregulatory strain compared to TEMP. However, this appears to have no effect on cytokine profile and minimal effect on intestinal epithelial injury and gastrointestinal symptoms.