Abstract
In industrialised areas of Europe, North America, Australia and New Zealand, vitamin B12 deficiency during infancy is thought to be uncommon and the majority of reported cases are in exclusively breastfed infants of mothers consuming vegetarian or vegan diets. We describe a breastfed infant whose mother eats a very diverse diet who developed growth failure, refusal to wean from the breast or eat solid foods and irritability as a result of profound vitamin B12 deficiency caused by unrecognised maternal vitamin B12 deficiency likely secondary to asymptomatic atrophic gastritis and pernicious anaemia. Recent literature suggests vitamin B12 deficiency in breastfed infants is much more common than previously recognised and this case emphasises the importance of considering the possibility of vitamin B12 deficiency in any breastfed infant with poor growth, neurologic symptoms or signs, developmental delay and/or feeding difficulties, particularly difficulty with introduction of complementary foods or weaning from the breast.