Which vitamin deficiency can cause both anemia and peripheral neuropathy?

• A. Thiamin
• B. Vitamin B12
• C. Folate
• D. Zinc

Answer: (B)

Vitamin B12 deficiency is the one that can cause both anemia and peripheral neuropathy. It is essential for two key processes: DNA synthesis in hematopoietic cells and maintenance of myelin in peripheral nerves. Without B12, DNA synthesis is impaired, leading to megaloblastic (macrocytic) anemia. At the same time, disruption of myelin maintenance causes peripheral neuropathy, with symptoms like numbness, tingling, and gait problems. Mechanistically, B12 is a cofactor for methionine synthase (linking to folate recycling and DNA synthesis) and methylmalonyl-CoA mutase (linked to myelin integrity); its deficiency thus explains the dual presentation. Other deficiencies may cause one feature (for example, folate deficiency causes macrocytic anemia) but not neuropathy, while thiamin can cause neuropathy as well but not the characteristic anemia pattern described.