Assessing the relationship of gut microbiota with neurological, psychiatric, and neurodegenerative disorders: a narrative review

The gut-brain axis is a bidirectional communication network regulated by the immune, nervous, and endocrine systems, microbial metabolites, and environmental factors such as diet, stress, circadian rhythm, and drugs/chemicals. This review aims to examine current literature on the link between gut microbiota dysbiosis and major brain disorders, and to explore strategies for improving patient outcomes. This narrative (non-systematic) review investigated the association between gut microbiota dysbiosis and psychiatric (schizophrenia, major depressive disorder, bipolar disorder, eating disorders), neurological (autism spectrum disorder, attention deficit hyperactivity disorder, epilepsy, migraine), and neurodegenerative disorders (Parkinson's disease, Alzheimer's disease, multiple sclerosis). It also considered potential microbiota- and neuroprotective interventions. The existing body of evidence consistently links gut dysbiosis with neuropsychiatric and neurodegenerative conditions through mechanisms including inflammation, impaired intestinal barriers, microbial production of neurotransmitters or toxins, and accumulation of α-synuclein or amyloid affecting neurogenesis and myelination. Balanced dietary patterns and the use of probiotics, prebiotics, or fermented foods are associated with healthier gut microbiota and improved neurological function. Further research is needed to clarify whether gut dysbiosis causes or contributes to these disorders, and to develop evidence-based, gut-focused practical recommendations for their prevention and management.