Vitamin B12 Deficiency in Children: Causes, Presentation, and Management

Vitamin B12 deficiency in children is uncommon but consequential — the developing nervous system is exquisitely sensitive to cobalamin deprivation. Early diagnosis prevents permanent neurodevelopmental impairment.

Etiology

• Maternal deficiency: Vegan/vegetarian mother, pernicious anemia, or gastric surgery → low fetal stores and low breast milk B12. Infant typically presents at 3–12 months.
• Dietary: Vegan/vegetarian child without supplementation, macrobiotic diets, food insecurity.
• Malabsorption: Celiac disease, Crohn's, SIBO, tropical sprue, pancreatic insufficiency.
• Genetic: Imerslund-Gräsbeck (IF receptor), transcobalamin II deficiency, methylmalonic acidemias (MMA), cblC/D/E/F/G/J defects.
• Drug-induced: Metformin (pediatric type 2 diabetes), PPIs, H2RAs.
• Nitrous oxide exposure: Repeated anesthesia/sedation oxidizes B12.

Clinical Presentation (Age-Dependent)

Age Group	Typical Features
Infant (3–12 mo)	Failure to thrive, hypotonia, developmental delay/regression, irritability, lethargy, feeding difficulties, megaloblastic anemia, seizures, microcephaly, movement disorders (tremor, chorea).
Toddler/Preschool	Gait disturbance, speech delay, behavioral regression, anemia, glossitis, recurrent infections.
School-Age/Adolescent	Fatigue, weakness, paresthesias, gait ataxia, cognitive decline, psychiatric symptoms (depression, psychosis), menstrual irregularities, subacute combined degeneration.

Diagnosis

• Serum B12, MMA, homocysteine — same panel as adults, using age-adjusted references (children have higher baseline B12).
• CBC + peripheral smear: macro-ovalocytes, hypersegmented neutrophils.
• Genetic testing if congenital/early onset, family history, or atypical presentation.
• Maternal B12 status assessment for infants.

Treatment

• Acute/severe (neurologic symptoms): IM cyanocobalamin 1000 mcg (or weight-based 10–50 mcg/kg) daily × 1–2 weeks → weekly × 4 weeks → monthly.
• Mild/dietary: High-dose oral (1000–2000 mcg/day) or nasal spray — effective even with malabsorption via 1% passive diffusion.
• Genetic disorders: Lifelong parenteral (IM/SC) or very high-dose oral; metabolic cofactor therapy (carnitine, biotin for MMA).
• Dietary correction: Fortified foods (plant milks, cereals, nutritional yeast) + supplement for vegan children. RDA: 0.9–2.4 mcg/day by age.

Monitoring & Follow-Up

• Clinical: neurodevelopmental milestones, growth, hematologic normalization.
• Labs: B12, MMA, Hb/MCV at 1, 3, 6, 12 months then annually.
• Screen siblings if genetic or maternal cause identified.

Prevention

• Screen pregnant vegans/vegetarians for B12; supplement adequately.
• All vegan children: daily B12 supplement (cyanocobalamin 5–25 mcg/day by age) or reliable fortified foods at every meal.
• Monitor B12 in children on long-term metformin/PPI.
• Newborn screening detects some inborn errors (MMA, cbl defects).

Pediatric B12 deficiency is a neurologic emergency when symptomatic. The cost of a $10/year supplement is infinitesimal compared to the cost of a child's lost potential. Supplement vegan kids. Screen at-risk moms. Think B12 in any infant with hypotonia, regression, or anemia.