Metformin is a commonly prescribed medication for people with type 2 diabetes and was originally marketed under the name Glucophage. While it is widely used to support blood sugar control, research suggests that long-term metformin use may influence vitamin B12 status in some patients.

A study published in Revista da Associação Médica Brasileira (January–February 2011; 57(1):46–49) evaluated 144 patients with type 2 diabetes who were being treated with metformin. Researchers measured serum vitamin B12 levels and analyzed their relationship to age and duration of metformin use.

The results showed that:

  • Nearly 7% of patients had serum vitamin B12 levels below 125 pmol/L, a range commonly considered deficient

  • Approximately 37% of patients had levels between 125 and 250 pmol/L, a range often described as borderline or suboptimal

  • Vitamin B12 levels were lower in older patients

  • Vitamin B12 levels declined with longer duration of metformin use

The authors concluded that these findings suggest a potential need for vitamin B12 support in some patients taking metformin. This concern is heightened by the fact that standard serum B12 testing may fail to identify many individuals with functionally low B12 status.

Why Vitamin B12 Matters

Vitamin B12 plays a central role in energy production, neurological function, red blood cell formation, and methylation pathways. Symptoms associated with low B12 status can include:

With more advanced deficiency, vitamin B12 depletion can contribute to pernicious anemia and significant neurological impairment. In some cases, memory loss and confusion related to B12 deficiency can resemble Alzheimer’s disease, underscoring the importance of recognizing and addressing low B12 status early.

Context

This research adds to a growing body of literature linking metformin use with altered vitamin B12 levels. While not all patients taking metformin experience B12 depletion, these findings suggest that duration of use and age may influence risk, and that serum testing alone may not provide a complete picture of B12 status.