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

TLDR

Gastrointestinal symptoms are common among soldiers in combat or high‑pressure situations, and are thought to arise from neuroendocrine dysregulation, immune activation, and increased intestinal permeability. The study aimed to examine how prolonged, intense mixed psychological and physical stress during combat training affects intestinal permeability, systemic inflammatory and stress markers, and to identify high‑risk subgroups for future protective interventions. Thirty‑seven male army medical rapid‑response troops had GI symptoms, stress markers, segmental intestinal permeability (via a 4‑sugar test), and immune activation measured during the fourth week of intense combat training and a rest period. Combat training increased stress, anxiety, depression, GI symptom severity, serum cortisol, IL‑6, TNF‑α, and intestinal permeability, with higher lactulose:mannitol ratios in soldiers with severe GI symptoms, indicating that prolonged combat training induces stress‑related GI dysfunction and pro‑inflammatory immune activation.

Abstract

Summary 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‐α, 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.