Causes of vitamin B12 deficiency
| Common causes (related to malabsorption) |
| Autoimmune gastritis (pernicious anemia) |
| Celiac disease |
| Inflammatory bowel disease |
| Surgical gastrectomy, gastric bypass, ileal resection |
| Less common causes |
| Nutritional (strict vegans, breastfed infants of mothers with vitamin B12 deficiency) |
| Nitrous oxide abuse |
| Diphyllobothrium latum infection |
| Pancreatic insufficiency |
| Drug effect (metformin, proton pump inhibitors) |
| Inherited disorders affecting intrinsic factor or the cubam receptor |
| Rare inherited disorder (eg, methylmalonic acidemia, transcobalamin II deficiency) |
Information from references 4, 5, and 7.