Which conditions increase the risk for megaloblastic anemia due to vitamin B12 deficiency?

Megaloblastic anemia due to vitamin B12 deficiency occurs when there is inadequate availability or absorption of vitamin B12, which is essential for proper DNA synthesis and red blood cell production.

Veganism significantly increases the risk of vitamin B12 deficiency because plant-based diets typically lack sufficient sources of this vitamin, which is primarily found in animal products. Individuals following a vegan diet may not consume enough B12 unless they take supplements or consume fortified foods.

Pernicious anemia is an autoimmune condition characterized by the inability to absorb vitamin B12 due to the destruction of cells in the stomach that produce intrinsic factor, a protein necessary for B12 absorption. This condition directly leads to a deficiency of vitamin B12.

Crohn's disease, a form of inflammatory bowel disease, can lead to malabsorption of various nutrients, including vitamin B12, especially if the terminal ileum, where B12 is absorbed, is affected. The inflammation and damage to the intestinal lining impair the body’s ability to properly absorb essential nutrients.

These three conditions—veganism, pernicious anemia, and Crohn disease—are all linked to an increased risk for developing megaloblastic anemia due to vitamin B12 deficiency, making this option correct.