Vitamin B12 Deficiency on Long-Term Metformin and Proton Pump Inhibitors: A Case for Scheduled Testing
DOI:
https://doi.org/10.5281/zenodo.22278558Keywords:
Vitamin B12, Metformin, Proton pump inhibitors, Monitoring, PolypharmacyAbstract
The two drugs named in the title do not carry equal evidence. Metformin is established: it reduces serum B12 in 10 to 30 per cent
of users, a regulator has reclassified low B12 as a common side effect affecting up to one in ten, and in a study of 231 matched
pairs deficiency was present in 22.5 against 7.4 per cent, persisting at 17.9 against 5.6 per cent after acid-suppressant users were
excluded. For proton pump inhibitors the evidence conflicts: one systematic review found no difference in serum B12 between
users and controls, with a standardised mean difference of 0.01 (p = 0.92), while an earlier meta-analysis of acid-lowering drugs
reported a hazard ratio of 1.83 using inconsistent deficiency criteria. Testing meanwhile is uncommon: in 104 patients taking both
agents, 13.5 per cent had a documented level and none was deficient.
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