How is vitamin B12 absorbed, and who is at higher risk of deficiency?

• A. B12 is absorbed in the ileum with intrinsic factor; higher risk in older adults and those with pernicious anemia or vegan diets.
• B. B12 absorbed in the stomach without intrinsic factor.
• C. B12 absorbed in the colon; risk in athletes.
• D. B12 absorbed in the jejunum with pancreatic enzymes; risk in older adults.

Answer: (A)

Vitamin B12 absorption relies on intrinsic factor produced in the stomach. The B12-IF complex travels to the ileum, where it binds to receptors and is absorbed. This is why deficiency risk is higher when intrinsic factor is absent or reduced—such as in pernicious anemia or gastric atrophy common in older adults. Vegan diets also raise risk because B12 is mainly found in animal products. The other options mistake where absorption occurs or omit the essential role of intrinsic factor.