What is the most common cause of megaloblastic anemia?

The most common cause of megaloblastic anemia is vitamin B12 deficiency. This condition arises because vitamin B12 is crucial in DNA synthesis, and its lack leads to improper red blood cell formation, resulting in larger-than-normal cells (megaloblasts) in the bone marrow. This deficiency can stem from various factors, including dietary insufficiency, malabsorption syndromes, or conditions like pernicious anemia, which directly inhibits the absorption of B12.

While pernicious anemia is a specific type of vitamin B12 deficiency caused by an intrinsic factor deficiency, it is not the most common cause of megaloblastic anemia overall. In practice, vitamin B12 deficiency is more routinely encountered as it can result from a broader range of dietary and health factors. Folate deficiency is also a significant cause of megaloblastic anemia but is less common than vitamin B12 deficiency in practice. Iatrogenesis refers to anemia induced by medical interventions and is not a primary cause of megaloblastic anemia.