Why is B12 deficiency a concern after gastrectomy?

Why is B12 deficiency a concern after gastrectomy?

• A. There is no longer adequate intrinsic factor to bind with B12, reducing absorption.
• B. B12 is produced by the liver and is depleted after gastrectomy.
• C. B12 is absorbed in the colon, which is removed.
• D. B12 does not require intrinsic factor for absorption.

Answer: (A)

The main idea is that vitamin B12 absorption depends on intrinsic factor produced by gastric parietal cells. A gastrectomy removes part or all of the stomach, including these cells, leading to little or no intrinsic factor being produced. Without sufficient intrinsic factor, the B12–intrinsic factor complex cannot form and be efficiently absorbed in the terminal ileum, so B12 absorption drops and deficiency can develop over time. The body can absorb a small amount of B12 passively without intrinsic factor, but this amount is far too small to meet needs. Therefore, B12 deficiency is a real concern after gastrectomy, and management usually involves vitamin B12 replacement (often parenteral or high-dose oral) with monitoring of levels over time.

The main idea is that vitamin B12 absorption depends on intrinsic factor produced by gastric parietal cells. A gastrectomy removes part or all of the stomach, including these cells, leading to little or no intrinsic factor being produced. Without sufficient intrinsic factor, the B12–intrinsic factor complex cannot form and be efficiently absorbed in the terminal ileum, so B12 absorption drops and deficiency can develop over time. The body can absorb a small amount of B12 passively without intrinsic factor, but this amount is far too small to meet needs. Therefore, B12 deficiency is a real concern after gastrectomy, and management usually involves vitamin B12 replacement (often parenteral or high-dose oral) with monitoring of levels over time.