At present there are no guidelines recommending routine testing of vitamin B12 in metformin users, despite the very consistent data that B12 deficiency accompanies longer-term use of metformin. This study released today from the VA demonstrates that metformin users, compared to non-metformin users, more frequently had B12 deficiency (7.6% vs. 3.0%), and that metformin users were also more likely to have low, but not deficient levels of B12. Only about a third of veterans using metformin had testing for B12. These results are similar to other studies, suggesting that B12 levels should be routinely checked every several years in people taking metformin. The anemia and neuropathy accompanying vitamin B12 deficiency can easily be treated, but only when they have been diagnosed.
See abstract here.