Mechanisms of Bifidobacterium as an Adjuvant Therapy for Improving Sleep Quality and Neuroendocrine Regulation in Bipolar Disorder: A Narrative Review

Abstract

Bifidobacterium, a genus of beneficial gut bacteria, is widely recognised for regulating gut microbiota homeostasis, modulating immune function, and maintaining metabolic balance. Modern research suggests that it exerts regulatory effects on the gut–brain axis, thereby influencing central nervous system function and improving mental health outcomes. It may regulate neurotransmitters by promoting serotonin precursor synthesis and balancing dopamine release. It could restore the negative feedback of the hypothalamic–pituitary–adrenal axis and optimise the function of the hypothalamic–pituitary–thyroid axis. Additionally, it may suppress inflammatory cytokines, regulate tryptophan metabolism, and maintain immune cell homeostasis. Regarding sleep improvement, it might act by regulating circadian clock genes and gut–brain axis-mediated central inhibitory pathways. Preliminary clinical evidence shows that its combination with conventional treatments may enhance sleep efficiency and mood in patients with depression, with good safety profiles. Despite the lack of large-scale studies evaluating the application of Bifidobacterium in bipolar disorder (BD), and the fact that no sufficient scientific evidence currently supports its direct treatment of BD, its multi-system regulatory properties align closely with the pathological mechanisms of BD, suggesting its potential as a novel option for the comprehensive management of BD-related sleep disturbances and hormone imbalances.