The need for vitamin B12 and folic acid inthe formation of red blood cells is related primarily of their effects on:
Synthesis and release of erythropoietin from the kidney
Absorption of iron from the gut
DNA synthesis in bone marrow
Hemoglobin formation in the red blood cell
Within 6-9 hours of treatment with vitamin B12 formation of nuclear DNA component promotes normoblastic reaction of the bone marrow. Folic acid also promotes the formation of nucleic acids.