The Role and Mechanisms of Probiotic Supplementation on Depressive Symptoms: A Narrative Review.

PURPOSE OF REVIEW: The microbiota-gut-brain-axis (MGBA) plays a role in the aetiology of mental disorders. Depression, a leading cause of disability worldwide, may be improved by probiotics. The aim of this narrative review is to investigate and synthesize the current evidence linking probiotic food supplementation with depressive symptomology.

RECENT FINDINGS: The gut and the brain communicate and interact via the MGBA through inflammation and the immune system, short chain fatty acid production, neuronal innervation and activation as well as endocrine and neurotransmitter modulation. Dysregulation of gut-brain pathways are caused by gut dysbiosis and implicated in the onset, persistence and exacerbation of depression related symptoms. Modulation of the gut microbiota via administration of probiotics has shown to reduce depressive symptom severity with Bifidobacterium and Lactobacillus strains being the most reported. Probiotics may produce greater benefits in mild depression rather than in chronic, treatment resistant depression. Probiotic supplementation is a promising and safe approach for the prevention of severe depressive disorders in high-risk individuals such as people with subthreshold depression. However, the mechanistic pathways of the MGBA require further investigation and additional human clinical trials are necessary to evaluate the role of probiotics on depression.