Causes of vitamin B12 deficiency anemia

A vitamin is a substance the body needs but doesn't make. Most people get more than enough vitamin B12 by eating foods such as meat, eggs, and milk products. Vitamin B12 deficiency anemia usually develops when the body cannot absorb this vitamin from food. This can happen if:

• You have pernicious anemia. This inherited condition is caused by the lack of a substance in your stomach called intrinsic factor. Your body needs intrinsic factor in order to absorb vitamin B12 from food. Pernicious anemia is most common in older adults. It is more common among people in certain parts of the world, especially Scandinavia.
• You have had surgery to remove all or most of your stomach or the last section of your small intestine (ileum). If this part of the small intestine is removed, your body cannot absorb enough vitamin B12. For example, certain types of bariatric surgery of the stomach, used to help with weight loss in people who are very overweight, can also lead to vitamin B12 deficiency anemia.¹
• You take medicine to treat heartburn and ulcers for a long time. Examples of these medications include omeprazole (Prilosec) and lansoprazole (Prevacid).²
• You have a problem with your digestive tract, such as sprue (also called celiac disease), Crohn's disease, a parasite, or bacteria growth.
• Your pancreas doesn't work properly.

More rarely, this condition develops if you don't have enough vitamin B12 in your diet. Those at higher risk include people who eat a strict vegetarian (vegan) diet, older adults who don't eat a variety of foods, and people with chronic alcoholism. The babies of women who eat a vegan diet are also at risk.