ABSTRACT
Key Clinical Message: It is important for pregnant and breastfeeding women who adhere to a strict vegetarian diet to take appropriate steps to avoid vitamin B12 deficiency in their infants. Abstract: Vitamin B12 deficiency is rare during infancy. The initial symptoms of this deficiency are subtle and may include irritability, failure to thrive with a decline in growth rate, apathy, anorexia, refusal of solid foods, megaloblastic anemia, and developmental regression. The case presented here involves an 8-month-old male infant who showed neurological symptoms such as decreased activity, increased drowsiness, and reduced interaction with parents, which were ultimately linked to a deficiency of cobalamin (vitamin B12). Early recognition of this condition is critical because it is reversible. Therefore, pregnant and lactating women who follow a strict vegetarian diet should take necessary measures to prevent vitamin B12 deficiency in infants.