Insomnia is one of the most common sleep disorders. Traditionally, its pathophysiology has been interpreted mainly from the perspective of the central nervous system (CNS). However, accumulating evidence suggests that the microbiota-gut-brain axis (MGBA), a bidirectional communication network linking the gut and the CNS, may play an important role in the development, maintenance, and treatment of insomnia. This review summarizes the major signaling pathways of the MGBA and discusses its potential mechanisms in insomnia. Current evidence indicates that gut microbiota and their metabolites may influence sleep-wake homeostasis through neural, immune, endocrine, and circadian pathways. At the same time, insomnia-related stress responses, immune imbalance, and lifestyle disturbances may in turn affect the gut microbiota, thereby forming a bidirectional regulatory network. Animal and clinical studies further support a close association between gut microbial dysbiosis and insomnia. In addition, this review systematically summarizes factors that may affect the MGBA, including diet, lifestyle, psychosocial stress, medications, and medical exposures. On this basis, MGBA-targeted interventions, such as dietary modification, prebiotics and probiotics, lifestyle interventions, fecal microbiota transplantation, and natural medicines, may provide promising new strategies for the prevention and treatment of insomnia. Nevertheless, the current evidence still relies largely on animal studies and cross-sectional research, and further longitudinal studies and high-quality interventional trials are needed to clarify causality, long-term efficacy, and standardized therapeutic approaches.
Keywords: fecal microbiota transplantation; gut microbiota; insomnia; microbial metabolites; microbiota–gut–brain axis; probiotics; sleep disorders; sleep–wake cycle.