Advances in understanding intestinal microbiota mechanisms and intervention strategies for anxiety, depression, sleep disorders, and constipation.

Anxiety, depressive symptoms, sleep disorders, and chronic constipation frequently co-occur and collectively impose a substantial clinical burden. Although these conditions may involve partially overlapping neural, endocrine, immune, and metabolic processes, their shared pathophysiological basis has not been fully established. This narrative review examines the potential role of the microbiota-gut-brain axis in linking affective symptoms, sleep disturbances, and chronic constipation. Evidence from human observational studies, Mendelian randomization analyses, animal models, and preliminary interventional studies suggests that alterations in gut microbial composition and function may contribute to these clinical associations through microbial metabolites, immune signaling, neuroendocrine regulation, and neural pathways. The review also summarizes microbiota-targeted interventions, including probiotics, prebiotics, dietary modification, and fecal microbiota transplantation. However, substantial heterogeneity in study populations, microbial findings, experimental methods, and intervention protocols limits causal interpretation and clinical generalization. A more rigorous distinction among associative, mechanistic, genetic, and interventional evidence is therefore required when evaluating the therapeutic potential of microbiota-based strategies.