How do vitamin B12 and folic acid deficiencies affect red blood cell production?

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blood disease Peripheral blood smear revealing histopathologic features indicative of a blast crisis in a case of chronic myelogenous leukemia (CML). Blast crisis occurs when one-fifth to one-third of the cells in the blood or bone marrow are immature blood cells, or blast cells. This phase of CML is characterized by fever, weakness, and an enlarged spleen.

Deficiencies in vitamin B12 or folic acid disrupt red blood cell production by impairing DNA synthesis, which is essential for proper cell maturation.1

When these vitamins are lacking, the bone marrow produces abnormal, large nucleated red cells called megaloblasts. Although marrow cells continue to proliferate, they fail to mature correctly, leading to ineffective erythropoiesis. This process results in:1

Megaloblastic Anemia: The formation of mature red blood cells that are larger than normal, known as macrocytic anemia.1
Reduced Cell Counts: A decrease in the number of young red cells (reticulocytes), as well as a reduction in granulocytes and platelets.1
Accelerated Destruction: The ineffective red cells are destroyed at a rate faster than normal, a feature characteristic of hemolytic anemia.1

While oral folic acid can relieve the anemia, it is critical to address vitamin B12 deficiency specifically, as failing to do so can lead to irreversible damage to the nervous system.1