Deciphering the role of probiotics in mental health: a systematic literature review of psychobiotics.

Probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit to the host. The selection criteria for probiotics include strain safety, viability, tolerance, metabolite production and/or the ability to modulate the immune system. Probiotics are commonly used in industries, such as food, agriculture, medicine, biotechnology, pharmaceuticals, and aquaculture. Recently, the medicinal applications of probiotics have gained attention and are being explored for the prevention and treatment of various diseases. One emerging area of interest is their potential role in psychological disorders. Mental illnesses, characterised by disturbances in behaviour, mood, thinking, and emotions, affect over one billion people globally. While various preventive and treatment options for mental disorders exists, each is associated with certain limitations. A new avenue being explored is the gut-brain axis, a complex bi-directional communication between the gut and the brain, that is facilitated by hormonal, neuronal, humoral, and immunological pathways. This system plays an important role in mental health. Probiotics, as a key modulator of the gut microbiome, could play a vital role in this communication. However, the underlying mechanisms remain to be explored. Probiotics may act through the production of metabolites and neuroactive substances, as well as through immunomodulation and cytokine production. Current data shows promising effects on stress, mood, and depression, presenting probiotics as a potential natural treatment option for psychological disorders. Nevertheless, major limitations in the existing research include insufficient clinical outcomes, limited sample sizes, and variable dosing. Future advancements may be achieved through stratifications based on gut microbiota, the use of next-generation probiotic strains, and the conduct of comprehensive validation studies.