Metformin Users With Diabetes Less Likely to Be Tested for Vitamin B12 Status

Although long-term metformin therapy is associated with lower serum vitamin B12 concentration, high-risk users are often not monitored for vitamin B12 deficiency.

In a study published in the Journal of the American Geriatrics Society, investigators sought to examine the association between long-term metformin therapy and serum vitamin B12 monitoring.

The retrospective cohort study included 3687 veterans 50 years or older with type 2 diabetes and long-term metformin therapy, and 13,258 veterans without diabetes and no prescription for metformin, recruited from a single Veterans Affairs Medical Center (VAMC).

Diabetes status was determined from outpatient visits, and long-term metformin therapy was defined as a prescription ≥500 mg/d for at least 6 consecutive months. The investigators estimated the proportion of participants who received a serum B12 test and used a multivariable logistic regression—–stratified by age­­––to evaluate the association between metformin use and serum B12 testing.

The results of the study showed that of the patients with diabetes receiving metformin, only 37% were tested for vitamin B12 status after long-term metformin prescription.

In the metformin-exposed group, the mean B12 concentration was significantly lower compared with the group without diabetes.

Approximately 7% of study participants administered metformin had a vitamin B12 deficiency compared with 3% of patients without diabetes or metformin use.

Dependent on age, metformin users were 2 to 3 times more likely not to receive vitamin B12 testing compared with those without metformin exposure, according to the study. The findings were the same after adjusting for sex, race/ethnicity, body mass index, and number of years treated at the VAMC.

“Long-term metformin therapy is significantly associated with lower serum vitamin B12 concentrations, yet those at risk are often not monitored for B12 deficiency,” the authors wrote. “Because metformin is first-line therapy for type 2 diabetes, clinical decision support should be considered to promote serum B12 monitoring among long-term metformin users for timely identification of the potential need for B12 replacement.”