The body does not make vitamin B12 so it must get it from foods or supplements. A deficiency in B12 can be caused by not getting enough of the vitamin or by some other factor.
• Diet lacking foods with B12.
• Surgery removing parts of the stomach (like gastric bypass) or the last part of the small intestine (ileum).
• Digestive problems, such as Crohn's disease, celiac disease, or parasites.
• Lack of a substance called intrinsic factor (IF). B12 is dependent upon this substance to make its way from the gastrointestinal tract to the rest of the body.
• Insufficient secretion of stomach acid. Stomach acid is needed to release B12 from the proteins in the food.
• Vitamin B6 deficiency. B6 is necessary for the proper absorption of B12.
• Vitamin E deficiency. E is needed to convert B12 from its non-active form into its biologically active form.
• Long-term use of antacids or ulcer medications.