Evidence check: Cortisol in the context of Darmgesundheit

Cortisol, the primary stress hormone, has a bidirectional relationship with gut health. Through the hypothalamic-pituitary-adrenal (HPA) axis and the vagus nerve, the gut and brain communicate. A compromised gut barrier ('leaky gut') and microbial dysbiosis can trigger low-grade inflammation, which in turn overactivates the HPA axis, raising cortisol levels. Conversely, chronically elevated cortisol reduces gut blood flow, impairs mucus production, and alters the gut microbiota composition. Evidence comes mainly from animal models and human observational studies; robust randomized controlled trials demonstrating a clear causal chain are scarce. Probiotics, dietary fiber, and stress management may positively influence the gut–brain axis, but individual cortisol responses vary. Commercial tests (stool or saliva) can offer clues but do not replace clinical diagnostics. Their predictive value is limited because cortisol follows a circadian rhythm and is affected by many confounders. Overall, the link between gut health and cortisol is plausible and supported by moderate evidence, but it is not yet sufficient for personalized interventions without medical supervision.