Risk factors for vitamin B12 deficiency anemia include:

• Long-term (chronic) inflammation of the stomach (atrophic gastritis).
• Pregnancy or breast-feeding.
• Removal of all or part of the stomach (gastrectomy), gastric bypass surgery, or gastric stapling surgery.
• Problems of the small intestine (ileum) where vitamin B12 is absorbed.
• Certain parasite infections, such as a fish tapeworm.
• Conditions such as inflammatory bowel disease.
• Not eating meat, eggs, or dairy products. Vitamin B12 is found only in foods that come from animals. Strict vegetarians (vegans) who do not eat milk, meat, or cheese can prevent having a vitamin B12 deficiency by taking supplements or multivitamins that contain vitamin B12.
• Long-term use of certain medications to treat ulcers, such as omeprazole (Prilosec) and lansoprazole (Prevacid).
• Alcoholism.