what are the causes of b12 deficiency?
['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."]