Table 3.

Causes of vitamin B12 deficiency

Food	Decreased consumption – vegan diet, food cobalamin malabsorption (more common in elderly)
Stomach	Pernicious anemia, partial or total gastrectomy, gastric bypass, atrophic gastritis, Helicobacter pylori infection, Zollinger–Ellison syndrome
Intestine	Chronic pancreatitis, bacterial overgrowth, fish tapeworm infestation, celiac disease, tropical sprue, Imerslund–Grasbeck disease, intestinal stagnant loop syndrome, ileal resection (>1.2 m), HIV
Drugs	Proton pump inhibitors, H2 blockers, nitric oxide anesthesia