Combat-training increases intestinal permeability, immune activation and gastrointestinal symptoms in soldiers

Background Gastrointestinal (GI) symptoms are common in soldiers in combat or high-pressure operational situations and often lead to compromised performance. Underlying mechanisms are unclear, but neuroendocrine dysregulation, immune activation and increased intestinal permeability may be involved in stress-related GI dysfunction. Aim To study the effects of prolonged, intense, mixed psychological and physical stress on intestinal permeability, systemic inflammatory and stress markers in soldiers during high-intensity combat-training. Methods In 37 male army medical rapid response troops, GI symptoms, stress markers, segmental intestinal permeability using the 4-sugar test (sucrose, lactulose, mannitol and sucralose) and immune activation were assessed during the 4th week of an intense combat-training and a rest period. Results Combat-training elicited higher stress, anxiety and depression scores (all P<0.01) as well as greater incidence and severity of GI symptoms [irritable bowel syndrome symptom severity score (IBS-SSS), P<0.05] compared with rest. The IBS-SSS correlated with depression (r=0.41, P<0.01) and stress (r=0.40, P<0.01) ratings. Serum levels of cortisol, interleukin-6, and tumour necrosis factor-, and segmental GI permeability increased during combat-training compared with rest (all P<0.05). The lactulose:mannitol ratio was higher in soldiers with GI symptoms (IBS-SSS 75) during combat-training than those without (IBS-SSS <75) (P<0.05). Conclusions Prolonged combat-training not only induces the expected increases in stress, anxiety and depression, but also GI symptoms, pro-inflammatory immune activation and increased intestinal permeability. Identification of subgroups of individuals at high-risk of GI compromise and of long-term deleterious effects of operational stress as well as the development of protective measures will be the focus of future studies.