From Gut to Brain: Probiotics as an Emerging Adjunctive Strategy for Insomnia and Sleep Disturbances.

OBJECTIVE: Too little sleep and incidental insomnia are two common conditions in which sleep is disrupted. Insomnia is often accompanied by emotional, metabolic, and immunological deterioration. The purpose of this narrative review is to better understand the gut-brain axis and evaluate the potential usefulness of probiotics in the treatment of insomnia and related sleep problems. METHODS: This study was designed as a narrative review of the literature on probiotics, gut microbiota, and sleep. A hierarchical method was used to synthesize mechanistic and clinical evidence, differentiating between upstream immune-inflammatory and HPA-axis control and downstream neuroactive metabolites and vagal signaling. Differences in probiotic strains, doses, intervention durations, and outcome measures were also investigated. As this study was designed as a narrative review rather than a systematic review, a formal risk-of-bias or quality assessment of the included randomized controlled trials was not performed. FINDINGS: Current research indicates that probiotics may regulate sleep via multiple gut-brain axis routes. Upstream processes in the proposed framework are immune-inflammatory modulation and hypothalamic-pituitary-adrenal (HPA) axis regulation, whereas downstream mediators are neuroactive metabolites and vagal signaling. Clinical research show that probiotics have small and diverse impacts on sleep outcomes, with improvements more frequently reported in subjective sleep assessments than objective tests. CONCLUSION: By altering the functioning of the brain-gut axis, probiotics may provide a emerging therapeutic option for insomnia. On the other hand, it is uncertain which probiotic strains and dosages will be most effective, as well as the relevant mechanisms; thus, additional well-controlled human intervention studies are warranted.