We appreciate the comments from Andrès and Federici and agree that food-cobalamin malabsorption accounts for metformin-associated vitamin B12 (cobalamin) deficiency.1 Whether the use of histamine2-receptor blockers or proton pump inhibitors confers an increased risk of vitamin B12 deficiency cannot be properly addressed in our study because it was impossible to ascertain the history of consuming those agents, either prescribed or, more importantly, purchased over the counter.
Chow KM, Ting RZ, Szeto CC. Metformin and Vitamin B12 Deficiency: Association and Not Causation May Play a Major Role in Cohort Studies—Reply. Arch Intern Med. 2007;167(7):730-731. doi:10.1001/archinte.167.7.730-b