Metformin and B12 Deficiency: A Bigger Problem Than We Thought

Charles P. Vega, MD


December 18, 2018

Hello. I'm Dr Charles Vega, and I am a clinical professor of family medicine at the University of California at Irvine. Welcome to Medscape Morning Report, our 1-minute news story for primary care.

Patients taking metformin should have their vitamin B12 levels assessed regularly to avoid peripheral nerve damage.

That's the conclusion from a single-center observational study[1] of more than 150 women conducted in the United Kingdom. On average, the women were 63 years old, were taking 2000 mg/day of metformin, and had been on the drug for about 6 years.

The majority of the women had not had their B12 levels measured. However, upon testing, almost 1 in 10 were found to have a B12 deficiency.

Although metformin is recommended for the first-line treatment of type 2 diabetes, it is associated with vitamin B12 deficiency, which itself increases the risk for peripheral neuropathy. Current guidelines do not recommend routinely checking B12 levels, although the British Society of Hematology recommends checking if there is a strong clinical suspicion.[2] Many patients with diabetes have peripheral neuropathy, and treatment with vitamin B12 in cases of deficiency can give clinicians something proactive with which to treat it.

Prior research has concluded that routine testing would not be cost-effective or clinically useful for people using this medication, but the authors of this study argue that it is time for that to change. While this one study may not warrant a guideline change, it is certainly something for those of us in clinical practice to keep in mind.


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