Which deficiency causes pernicious anemia?

• A. Vitamin B1
• B. Vitamin B12 (cobalamin)
• C. Vitamin C
• D. Vitamin K

Answer: (B)

Pernicious anemia occurs when the body can’t absorb enough vitamin B12 because intrinsic factor, a protein produced by stomach lining, is missing or blocked. Intrinsic factor is necessary for B12 uptake in the small intestine, so autoimmune destruction of the stomach’s parietal cells or the intrinsic factor itself leads to B12 deficiency even if dietary intake is adequate. Without sufficient B12, red blood cell precursors can’t complete DNA synthesis properly, so they become large and abnormal (megaloblastic), causing a characteristic type of anemia. This specific inability to absorb B12 distinguishes pernicious anemia from deficiencies of other vitamins: a lack of B1 causes other problems like beriberi, lack of vitamin C leads to scurvy, and lack of vitamin K affects blood clotting rather than red blood cell production.