Effect of previous night alcohol on symptoms and biomarkers of intestinal injury during prolonged physical activity in the heat

Physical work in the heat reduces splanchnic blood flow which can lead to gastrointestinal (GI) distress, intestinal injury, endotoxemia, and immune activation. Alcohol is known to affect these variables; however, it is unknown if previous night alcohol consumption has an additive effect on exertional heat stress performed the next morning. STUDY OBJECTIVE & HYPOTHESIS: We tested the hypothesis that GI symptoms and markers of intestinal injury, endotoxemia, and immune activation during prolonged physical activity in the heat would be exacerbated by previous night alcohol consumption. METHODOLOGY: Twelve healthy adults (5 males) completed exertional heat trials after a night of drinking alcohol (ALC) or a control trial of no alcohol consumption for ≥48 hours (CON), in a randomized crossover design. Each trial consisted of a 1-hr cycle, repeated four times, where participants walked on a treadmill in the heat (dry bulb temperature: 38°C, relative humidity: 40%) at an intensity corresponding to a metabolic rate of 4 W/kg for 20 min, 10 min at 8 W/kg, 20 min at 4 W/kg, and 10 min of seated rest. GI Symptoms were assessed at baseline and during rest periods using a validated 15-item questionnaire, which classified symptoms as “upper,” “lower,” or “other” symptoms. The GI symptoms for all time points were tallied prior to statistical analysis. Plasma samples were collected pre- and post-trial and used to measure markers of intestinal injury (intestinal fatty acid binding protein; I-FABP), endotoxemia (lipopolysaccharide binding protein; LBP), and immune activation (soluble cluster of differentiation 14; sCD14). RESULTS: There was 100% incidence of GI symptoms during ALC trials (median score: 32), which was significantly greater (p < 0.001) than CON (67% incidence, median score: 3). Upper (p = 0.002), lower (p = 0.006), and other (p = 0.004) GI symptoms were greater in the alcohol conditions. Specific symptoms included nausea (p = 0.008), bloating (p = 0.008), and dizziness (p = 0.008). Symptoms did not correspond to greater incidence of intestinal injury, as there were no effects of time (p = 0.82) or condition (p = 0.81) for I-FABP. However, there were effects of time (p = 0.002) and condition (p = 0.03) for sCD14, which increased from pre- to post-trial and was higher in the ALC (pre: 2025 ± 439 ng/mL, post: 2181 ± 420 ng/mL) condition compared to CON (pre: 1791 ± 405 ng/mL, post: 1954 ± 446 ng/mL). There were no effects of time (p = 0.29) or condition (p = 0.24) for LBP. CONCLUSIONS: Previous night alcohol increases GI distress during exertional heat stress, which was accompanied by elevated sCD14, indicating greater immune activation. Workers should avoid alcohol consumption prior to physical activity in hot environmental conditions to mitigate GI distress. Increased immune activation from previous night alcohol does not appear to be related to changes in GI injury or endotoxemia. FUNDING SOURCES: This study was partially funded by the University of New Mexico’s Research Allocations Committee (to FTA), GPSA (to JWS), and Graduate Studies (to JWS). This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.