Vitamin B12 deficiency, including pernicious anemia, is typically seen in malnourished individuals. Globally, it is widespread in those who live in poverty.

In the U.S., we often consider it in individuals who are chronic alcoholics. However, it can be seen in others, including:

• Bariatric patients after certain weight-loss surgeries
• Conditions causing problems with food digestion, including Crohn’s disease, celiac disease, or fish tapeworm (Diphyllobothrium latum) infection
• Individuals on certain medications for a prolonged time, including proton pump inhibitors, histamine 2 receptor blockers and metformin
• Inadequate dietary intake or genetic intrinsic factor deficiency