Pernicious anemia is often caused by a lack of intrinsic factor. The resulting vitamin deficiency is which?

• A. Vitamin C
• B. Vitamin B-12
• C. Folate
• D. Iron

Answer: (B)

Intrinsic factor is needed to absorb vitamin B12 in the small intestine. When intrinsic factor is lacking, vitamin B12 isn’t absorbed well, leading to a deficiency that causes pernicious anemia. Vitamin B12 is essential for proper DNA synthesis in red blood cell precursors and for maintaining myelin in nerves; without it, red blood cells become large and abnormal (macrocytic) and hematopoiesis falters. Folate deficiency can also cause macrocytic anemia, but pernicious anemia specifically involves a deficiency of vitamin B12 due to lack of intrinsic factor, not a lack of folate. Vitamin C deficiency causes scurvy, and iron deficiency causes microcytic anemia, so the vitamin involved here is vitamin B12.