Vitamin B12 supplementation for growth, development, and cognition in children

RATIONALE: supplementation in children. OBJECTIVES: supplementation on growth, development, and cognition in children less than 12 years of age. SEARCH METHODS: We searched CENTRAL, MEDLINE, Embase, 12 other databases, and two trial registries on 23 September 2025. We screened reference lists of studies. ELIGIBILITY CRITERIA: supplementation, alone or in combination with other micronutrients, in children < 12 years of age. We excluded cross-over trials, trials targeting pregnant or breastfeeding women, or participants with critical illnesses, and interventions delivered by intravenous/intramuscular injections. OUTCOMES: status, anaemia, haemoglobin, growth, cognitive function, developmental outcomes, and any adverse effects. Important outcomes included megaloblastic anaemia, body composition, health-related quality of life, morbidity, and all-cause mortality. RISK OF BIAS: We used Cochrane RoB 2 to evaluate bias. SYNTHESIS METHODS: We conducted meta-analyses using fixed-effect models. If there was substantial heterogeneity, we used random-effect models. When meta-analyses were not conducted, we described findings from individual trials, and considered synthesis and presentation of findings using other methods. We used GRADE to evaluate the certainty of evidence for critical outcomes. INCLUDED STUDIES: supplementation varied, ranging from 28 days to 31 months, with doses from 0.9 µg/day to 150 µg/day. Nine trials, including 2391 children, contributed data to meta-analyses. SYNTHESIS OF RESULTS: . There may be little to no difference between groups in anaemia (21.7% versus 25.0%; 1 trial, 35 children; low-certainty evidence). There may be little to no difference between groups in any adverse effects (9.2% versus 5.9%; 1 trial, 574 children; low-certainty evidence). The certainty of evidence for critical outcomes ranged from high to very low; we downgraded for imprecision due to small sample sizes or few events, risk of bias in outcome measurement, randomisation methods, selective reporting bias, or inconsistency due to substantial statistical heterogeneity. Few studies reported growth, cognition, development, anaemia, or any adverse effects. AUTHORS' CONCLUSIONS: . FUNDING: This review had no dedicated funding. REGISTRATION: Protocol available via DOI 10.1002/14651858.CD015264.