Background: Vitamin B12 deficiency is a recognized but frequently under-integrated cause of global developmental delay (GDD) in infancy and early childhood. Early diagnosis is critical because neurological impairment may be partially or completely reversible with timely treatment. Objective: This narrative review aims to synthesize current evidence on the role of vitamin B12 deficiency in the diagnostic evaluation of GDD, with a focus on clinical phenotype, risk factors, biomarkers, treatment outcomes, and practical integration into contemporary diagnostic algorithms. Methods: A structured, non-systematic search of PubMed/MEDLINE, Embase, and Web of Science was performed to identify clinical studies, case series, reviews, and guideline documents addressing pediatric vitamin B12 deficiency and neurodevelopmental delay. Results: Vitamin B12 deficiency in early childhood is most commonly associated with maternal deficiency and exclusive breastfeeding without adequate supplementation. Evidence from recent clinical and observational studies indicates that vitamin B12 deficiency may present with nonspecific neurological symptoms, including developmental regression, hypotonia, and feeding difficulties. Incorporating vitamin B12 assessment—using serum vitamin B12, holotranscobalamin, methylmalonic acid, and homocysteine—into early diagnostic algorithms for GDD may facilitate timely identification of a treatable cause of neurodevelopmental impairment. The proposed diagnostic framework emphasizes early biochemical evaluation in infants with unexplained developmental delay, thereby supporting prompt treatment during a critical window of neurological reversibility. Conclusions: Targeted assessment of vitamin B12 status in children with GDD, together with evaluation of maternal status, represents a clinically relevant approach to identifying a potentially preventable and treatable cause of neurodevelopmental impairment. Integration of functional biomarkers into diagnostic pathways and the development of pediatric-specific reference standards are key priorities for future research and clinical practice.

Background/objectives: Optimal infant nutrition, particularly exclusive breastfeeding for the first 6 months, is crucial for both immediate and long-term health. The early years of life are essential for brain development due of the rapid maturation of social, emotional, cognitive and motor capacities. While benefits of breastfeeding are well established, its long-term impact on neurodevelopment remains underexplored. This study investigates the relationship between breastfeeding duration and neurodevelopment outcomes at 5 years of age. Methods: This prospective cohort study followed 92 term-born infants in Varna, Bulgaria (2017–2024). Parents provided informed consent and completed questionnaires regarding demographic characteristics, feeding practices and atopic diseases. At 5 years of age, children were assessed using the Neurodevelopmental Test for Five-Year-Olds. Results: Feeding practices differed significantly across groups (p < 0.001), with exclusive breastfeeding more prevalent among children breastfed for longer. At 5 years, significant differences were observed in language development (p = 0.037) and behavioral outcomes (p = 0.001). A linear regression model for behavioral outcomes (F = 2.29, p = 0.011, R² = 0.297) showed that breastfeeding for 6–12 months was associated with more favorable behavior (Estimate = −5.88, p = 0.026), compared to less than 6 months. In contrast, paternal secondary education (Estimate = 3.58, p = 0.048) compared to higher education and mixed ethnicity (Estimate = 12.55, p = 0.023) compared with Bulgarian ethnicity were associated with poorer behavioral outcomes (Estimate = 3.58, p = 0.048). Conclusions: Breastfeeding for 6 to 12 months may be associated with improved behavioral development, and to a lesser extent, language outcomes at age five. However, these domain-specific associations were not consistently supported across all statistical methods and should be interpreted with caution. Neurodevelopment is influenced by a complex interplay of nutritional, social and environmental factors. Longitudinal studies are needed to clarify the long-term effects of breastfeeding duration on neurodevelopment.