In children, vitamin B12 (cobalamin) deficiency is a preventable cause of neurologic disorders that can be potentially irreversible if not identified and treated early. Its clinical presentation is variable and nonspecific, including hypotonia, psychomotor delay, apnea/brief resolved unexplained event (BRUE), and paroxysmal seizures, often without preceding anemia. This heterogeneity makes early diagnosis difficult and can delay treatment initiation, even though vitamin B12 supplementation is effective and safe. The recent literature highlights the role of expanded newborn screening and metabolic biomarkers as key tools for its early detection and the prevention of neurologic sequelae.1,2

Exclusive breastfeeding may be a risk factor for vitamin B12 deficiency in infants when the mother has low B12 levels or has not received adequate supplementation during pregnancy or lactation. The concentration of cobalamin in breast milk depends directly on maternal nutritional status; therefore, maternal deficiency is associated with reduced availability for the infant. Several studies have documented a high prevalence of hypocobalaminemia in breastfeeding women and exclusively breastfed infants, particularly in the context of vegetarian diets or diets low in animal products.3,4 These findings underscore the need to ensure adequate maternal supplementation during pregnancy and lactation.

We conducted a retrospective study of 153 patients with vitamin B12 deficiency managed at a tertiary care hospital between 2000 and 2024 with the aim of describing the epidemiological, clinical, and biochemical characteristics of this deficiency in the pediatric population and identifying associated risk factors. Patients were referred to the neurometabolic clinic from primary care, neonatal care, and pediatric inpatient care due to either clinical signs suggestive of B12 deficiency or incidental laboratory findings. The study was approved by the Clinical Research Ethics Committee of Aragón (file 14/2025) and authorized by the Teaching Committee of the hospital. Vitamin B12 deficiency was diagnosed based on the detection of serum B12 levels of less than 300 pg/mL or homocysteine levels greater than 6.5 mmol/L. The median age at diagnosis was 2 months (range, 15 days-4 years), with a predominance of the male sex (58.8%). Sixty-six percent of the patients were exclusively breastfed, and 50% of tested mothers had concomitant deficiency. Newborn screening allowed early identification in 25.5% of cases, before the onset of neurologic symptoms, in agreement with studies demonstrating the utility of expanded screening with total homocysteine (tHcy) and methylmalonic acid (MMA).2,5,6

Of the patients in whom vitamin B12 levels were measured, 67.3% were symptomatic. The predominant symptoms were hypotonia and feeding disorders in infants younger than 6 months; apnea and seizures in infants aged 7–12 months, and anemia in children aged more than one year. We performed a statistical analysis using the t test, analysis of variance, χ2 test, and nonparametric methods, considering P values of less than .05 statistically significant. We found a significant association between psychomotor delay and moderately low vitamin B12 levels (P = .03), suggesting that the severity of the deficiency is associated with the probability and severity of neurologic impairment. This finding was consistent with previous studies describing a proportional relationship between serum cobalamin concentration and the severity of neurodevelopmental impairment1,4 (Table 1).

From a biochemical standpoint, the correlation between serum levels of vitamin B12, homocysteine, and folic acid was evaluated using the Pearson correlation coefficient. We found a moderate and significant negative correlation between vitamin B12 and homocysteine (r = −0.260; P = .015), suggesting that as vitamin B12 concentrations increase, homocysteine levels tend to decrease. This finding supports the modulatory role of cobalamin in homocysteine metabolism. In contrast, the correlation between vitamin B12 and folic acid was very weak and not significant (r = 0.035; P = .744), suggesting the absence of a direct relationship between the two variables (Fig. 1; Table 2).

Figure 1.

Best-fit line and scatter plot for the correlation between vitamin B12 and homocysteine and serum folic acid.

In most patients, treatment was based on intramuscular hydroxocobalamin (83%), while the remaining patients received oral cyanocobalamin combined with folic acid supplementation or sequential combined oral-parenteral regimens, depending on clinical severity and the results of laboratory monitoring. Most patients showed rapid clinical improvement, particularly in hypotonia and paroxysmal episodes, and biochemical recovery was also observed post treatment. However, in some cases, there was only partial recovery from psychomotor delay, suggesting that neurologic damage may not be completely reversible when treatment is delayed.1 We were unable to accurately compare the time to biochemical normalization for the different treatment approaches due to the retrospective nature of the study and the heterogeneity of the laboratory follow-up.

The limitations of the study include its retrospective design and the absence of a control group, which preclude the establishment of causal relationships between the analyzed variables; therefore, the observed associations should be interpreted with caution.

In conclusion, the results of this case series support three key messages for pediatric practice:

• 1

  Vitamin B12 deficiency should be suspected in infants with nonspecific neurologic symptoms, even in the absence of anemia.

• 2

  Functional biomarkers (serum vitamin B12, homocysteine, and MMA) are essential diagnostic and monitoring tools.

• 3

  Expanded newborn screening and maternal supplementation during pregnancy and breastfeeding are key preventive strategies for reducing the incidence and sequelae of this deficiency.

These findings support a comprehensive approach to vitamin B12 deficiency in children, combining prevention, early detection, and timely treatment to prevent neurodevelopmental sequelae.