Question: what causes vitamin b12 not to be absorbed?
Answer: Atrophic gastritis, in which your stomach lining has thinned. Pernicious anemia, which makes it hard for your body to absorb vitamin B12. Conditions that affect your small intestine, such as Crohn's disease, celiac disease, bacterial growth, or a parasite. Immune system disorders, such as Graves' disease or lupus.