November 14, 2015

Metformin Has Link to Neuropathy, B12 Deficiency

Called me puzzled! I have never understood why the American Diabetes Association had never called for testing of vitamin B12 deficiency for people taking metformin for any length of time. Even this article shows a lack of this testing and only calls for more research. This is why I am reversing the situation and listing what Diabetes-in-Control lists as practice pearls first.

Practice Pearls:
  1. Metformin has been linked with vitamin B12 deficiency.
  2. A randomized placebo-controlled trial showed that metformin use is associated with an increase in neuropathy scores for patients.
  3. Current guidelines do not offer specific instructions on metformin and B12 deficiency, but future research is warranted.

Yes, one of the most common and beneficial T2DM drugs may contribute to neuropathy and vitamin deficiency – metformin.

The link between metformin and vitamin B12 lowering is well-known and mentioned in American Diabetes Association guidelines as a disadvantage of the drug. However, the ADA gives no recommendations for monitoring and prevention of vitamin B12 deficiency for patients taking metformin. Vitamin B12 deficiency is associated with adverse effects such as anemia, fatigue, mental status changes, and neuropathy. Given the prevalence of neuropathy in diabetic patients, metformin-induced vitamin B12 deficiency is clinically relevant.

The relationship between vitamin B12 deficiency and metformin was studied in a recent randomized placebo-controlled trial. The trial lasted 52 months and included 390 type 2 diabetes patients. They were treated with 850 mg metformin at doses up to three times a day or a placebo. Patients with baseline vitamin B12 deficiency or patients taking vitamin B12 supplements were excluded from the trial.

Metformin is prescribed around the world, so this relationship warrants more investigation according to the study authors. Future studies may clarify the relationship and will help the authors of guidelines decide whether to recommend testing or supplementation.

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