Long-term metformin use and vitamin B12 deficiency
The question: Why do people on metformin need their B12 checked?
- Study type
- Randomised controlled trial
- Participants
- 2,155
- Population
- Adults at high risk of type 2 diabetes in the US Diabetes Prevention Program
- Intervention
- Metformin, with open-label continuation
- Compared with
- Placebo
- Duration
- About 13 years of follow-up
- Published
- Journal of Clinical Endocrinology and Metabolism, 2016
What was measured
Blood B12 levels, anaemia and neuropathy.
What was found
Each year of metformin use was associated with a 13 per cent higher risk of B12 deficiency. Low or borderline B12 was more common with metformin, as was neuropathy among those with low B12.
Limitations
B12 was a secondary analysis. Low levels do not always cause symptoms.
What it means
Good reason for periodic B12 testing in people taking metformin long term, as the authors recommended.
Source
Aroda VR, Edelstein SL, Goldberg RB, et al. Long-term metformin use and vitamin B12 deficiency in the Diabetes Prevention Program Outcomes Study. J Clin Endocrinol Metab. 2016;101(4):1754-1761.
Read the original (DOI 10.1210/jc.2015-3754) · Source verified 8 October 2026
Study summaries describe published research for education. They are not claims about any product and are not medical advice.