Causes of vitamin B12 deficiency is: September 2006
**Core Concept**
Vitamin B12 deficiency is caused by impaired absorption, increased demand, or excessive loss of this essential nutrient. Vitamin B12 plays a crucial role in the synthesis of DNA, fatty acid, and amino acid metabolism.
**Why the Correct Answer is Right**
Vitamin B12 deficiency can occur due to various reasons, including impaired absorption from the gastrointestinal tract, which is mediated by intrinsic factor produced in the stomach. Intrinsic factor binds to vitamin B12 and facilitates its absorption in the terminal ileum. Deficiency can also result from increased demand, such as in pregnancy or malignancy, or excessive loss, often seen in conditions like celiac disease or Crohn's disease.
**Option A:**
Option A is incorrect because vitamin B12 deficiency is not typically caused by a lack of folic acid. Although folic acid deficiency can mask the symptoms of vitamin B12 deficiency, they are distinct entities with different pathophysiology.
**Option B:**
Option B is incorrect because vitamin B12 deficiency is not primarily caused by a lack of vitamin B6. While both vitamins are essential for various enzymatic reactions, their deficiency has distinct clinical manifestations.
**Option C:**
Option C is incorrect because vitamin B12 deficiency can be caused by impaired absorption, but not directly by a lack of intrinsic factor. Intrinsic factor is essential for vitamin B12 absorption, but the deficiency itself is a result of impaired absorption, not the lack of intrinsic factor.
**Option D:**
Option D is incorrect because vitamin B12 deficiency is not typically caused by a lack of vitamin D. Vitamin D deficiency has distinct clinical manifestations, including rickets and osteomalacia, which are different from those seen in vitamin B12 deficiency.
**Clinical Pearl / High-Yield Fact**
Vitamin B12 deficiency can cause neurological symptoms, including numbness, weakness, and gait disturbances, which can be irreversible if left untreated. Prompt diagnosis and treatment are essential to prevent long-term damage.
**Correct Answer: D. Deficiency of vitamin D.**