Mounting evidence suggests that early-life microbial colonization might shape cognitive development and behaviour. This systematic review summarizes current research on the relationship between the gut microbiota and neuropsychological development and behaviour in children and adolescents (0–18 years). Following PRISMA guidelines, we conducted a comprehensive search across MEDLINE, Scopus, and Web of Science, identifying 78 eligible studies covering both clinical neurodevelopmental disorders and general-population neuropsychological outcomes. We observed a high heterogeneity across studies regarding study design, statistical analyses and the consideration of confounding factors (e.g., diet, medication use), gut microbiota determinations and the assessment of neurobehavioural outcomes. Only 42% of studies used longitudinal designs, and confounding factors were frequently unaddressed. Microbiome alterations in autism spectrum disorder (n = 23 studies) included community structure shifts, elevated Clostridium and Sutterella , and reduced Blautia, Lactobacillus, and Bifidobacterium . Functional and metabolomic analyses suggest immunomodulatory and neuroactive processes as main contributors, including elevated levels of the short-chain fatty acids propionate and valerate. For attention-deficit/hyperactivity disorder (n = 7) findings were less consistent. Associations were modest in the general paediatric population, with Veillonella and Bifidobacterium appearing across multiple studies being more abundant in children with enhanced neuropsychological development. Overall, the evidence highlights potential microbial signatures associated with neurodevelopment, yet methodological limitations constrain causal inference. Most of the studies were of poor to fair quality, often due to technical shortcomings in microbiome assessment and statistical limitations. Future research should prioritize standardized exposure/outcome assessment protocols and multi-omics integration, while underlining the potential of methodological rigour in translating findings into clinically actionable knowledge. • The present systematic review synthesizes findings from 78 studies linking gut microbiota to neuropsychological and behavioural development from birth to adolescence. • In autism spectrum disorder, microbial alterations included elevated Clostridium and Sutterella , reduced Bifidobacterium , Lactobacillus , and Blautia , with functional evidence implicating neuroactive and immunomodulatory pathways. • Findings in attention-deficit/hyperactivity disorder were less consistent, yet Roseburia , Agathobacter , Coprobacillus and Bifidobacterium emerged as possible microbial signals. • In the general paediatric population, modest associations were observed, with Veillonella , Parabacteroides , Bifidobacterium , and Collinsella related to neuropsychological development. • Substantial heterogeneity in study design, exposure/outcome assessment, and analytical methods limited comparability; future studies should move towards harmonized protocols, longitudinal designs, and integrative multi-omic approaches.
Jiménez-Arenas et al. (Sun,) studied this question.