Increased Intestinal Permeability Does Not Associate With Gastrointestinal Symptoms At High Altitude

PURPOSE: Gastrointestinal (GI) barrier integrity may be compromised by acute high altitude (HA; >2,500 m) exposure resulting in increased GI permeability. Whether any increase in GI permeability contributes to GI symptoms or other altitude illness symptoms during HA sojourn is unknown. This study aimed to assess changes in GI permeability upon ascent to HA and to determine associations with GI symptoms and acute mountain sickness (AMS). METHODS: 78 healthy soldiers (90% male; 26 ± 5 yr) were tested at their baseline residence (BLR; 331 m (n = 41) or 1190 m (n = 37)), transported to Taos, NM (2845 m), then hiked (n = 39) or were driven (n = 39) to HA (3600 m), and stayed for four days (~68 hr). GI permeability was assessed by lipopolysaccharide binding protein (LBP) measured in fasted serum at BLR and each morning at HA ~20, 44, and 68 hr post-ascent. GI symptoms were measured daily and AMS-cerebral factor (AMS-C) scores were determined multiple times daily by questionnaire at BLR and HA. If AMS-C was ≥0.7 individuals were considered sick. Linear and generalized linear mixed models were used to determine changes in LBP concentrations and prevalence of GI symptoms and AMS over time and to assess associations. RESULTS: LBP concentrations were increased by 20% [95% CI: 6, 35] from BLR to the first morning of HA and remained elevated throughout the exposure (P = 0.001). Prevalence of GI symptoms, abdominal pain, bloating and discomfort, and nausea were all increased throughout HA (P < 0.01), with the odds of reporting any GI symptoms being 3.5 times [95% CI: 1.7, 7.1] higher at HA relative to BLR (P < 0.001). AMS prevalence was 31% on the first full day at HA and decreased to 9% by the final morning (P < 0.001). Reporting any GI symptoms was associated with a 3.6 times higher odds [95%CI: 1.6, 8.3] of experiencing AMS (P = 0.002). However, LBP concentrations were not associated with prevalence of GI symptoms or AMS at HA. Neither BLR nor method of ascent influenced LBP or GI symptom responses. CONCLUSION: Increased LBP concentrations are consistent with an increase in GI permeability following ascent to 3,600 m altitude. However, functional consequences are unclear as that increase did not associate with GI symptoms or AMS. Funded by USAMRDC and PRMRP