In obese patients, which deficiency is commonly due to metformin use?

• A. Vitamin A deficiency
• B. Vitamin C deficiency
• C. B12 deficiency due to metformin
• D. Vitamin D deficiency

Answer: (C)

Metformin can impair the absorption of vitamin B12 in the gut with long-term use, especially affecting the terminal ileum where the B12-intrinsic factor complex is taken up. This reduced absorption slowly depletes B12 stores and can lead to neuropathy, fatigue, or anemia—effects that can be mistaken for worsening diabetes. That makes B12 deficiency the most likely deficiency linked to metformin in obese patients. Other listed vitamins aren’t typically caused by metformin; vitamin D deficiency is common in obesity for other reasons, while vitamins A and C aren’t associated with metformin. If deficiency is suspected, checking serum B12 and providing supplementation is appropriate, and some evidence suggests ensuring adequate calcium intake can help improve B12 absorption.