Which of the following commonly contributes to macrocytic anemia?

Vitamin B12 deficiency is a well-known contributor to macrocytic anemia because it plays a crucial role in DNA synthesis and the production of red blood cells. When there is a deficiency of vitamin B12, the body is unable to produce red blood cells effectively, leading to a larger-than-normal size of the cells (macrocytes) that are produced. This results in macrocytic anemia, characterized by the presence of fewer but larger red blood cells.

In contrast, iron deficiency typically causes microcytic anemia, characterized by smaller red blood cells due to inadequate hemoglobin synthesis. Chronic disease can lead to anemia of inflammation or chronic disease, which is usually normocytic rather than macrocytic. Thalassemia, a genetic blood disorder affecting the production of hemoglobin, is also associated with microcytic anemia rather than macrocytic. Thus, the connection of vitamin B12 deficiency to macrocytic anemia is established through its critical role in normal red blood cell development and function.