Which anemia is primarily due to vitamin B12 deficiency?

Megaloblastic anemia is primarily due to vitamin B12 deficiency, as this deficiency affects DNA synthesis, leading to the production of abnormally large and immature red blood cells (megaloblasts) in the bone marrow. In the presence of inadequate vitamin B12, the process of erythropoiesis is disrupted, resulting in the hallmark features of megaloblastic anemia, which include macrocytic red blood cells and sometimes hypersegmented neutrophils.

Vitamin B12 plays a crucial role in the conversion of methylmalonyl-CoA to succinyl-CoA and in the synthesis of methionine from homocysteine. A deficiency can arise from various causes, such as inadequate dietary intake (particularly in vegetarians or those with malabsorption syndromes), pernicious anemia (where intrinsic factor is lacking, leading to impaired absorption), or certain gastrointestinal disorders.

In contrast, the other types of anemia listed do not primarily stem from vitamin B12 deficiency. For instance, normocytic anemia is characterized by red blood cells that are normal in size but still decreased in number, often due to chronic disease or acute blood loss, whereas hypoproliferative anemia results from underproduction of red blood cells due to factors