Low Vitamin B12 from Metformin Use

This topic is worth repeating. Many doctors do not believe patients when they are asked to be tested for low vitamin B12 deficiency. More studies are confirming this to be true. The one weakness is the length of time a patient has been taking metformin and the dosage taken for what length of time.

One of our support group members has been taking the maximum dosage of about 2250 mg for five years and has now been tested for vitamin B12 deficiency. He does not remember the amount, but said his doctor gave him a shot and had him back the following week for a second shot. He is now taking a supplement of 1000 mg daily. His doctor has said in another three months that he will be tested again to see if he needs another shot.

The doctor has asked him to move to insulin, but has allowed him to delay this until his next vitamin B12 test. He is talking to the rest of us taking insulin and Allen is talking to him because of his experience with vitamin B12 deficiency. Several others have encouraged him to no ignore the doctor as he is a veteran and his cost for insulin will be affordable.

Researchers found that those at risk for low vitamin B12 levels are often not properly monitored. According to a study published in the Journal of the American Geriatrics Society, long-term metformin use is significantly associated with lower serum vitamin B12 levels, but those at risk often are not monitored for this deficiency.

Researchers conducted a retrospective cohort study to evaluate the association between long-term metformin therapy and monitoring serum vitamin B12 at a single Veterans Affairs Medical Center (VAMC) from 2002–2012. Veterans aged over 49 years with either type 2 diabetes receiving long-term metformin therapy (n=3,687) or veterans without diabetes and no metformin prescription (n=13,258) were included in the study.

Long-term metformin therapy was defined as a prescription for greater than or equal to 500mg daily for greater than or equal to 6 consecutive months. The study showed that only 37 percent of older adults with diabetes receiving metformin were tested for vitamin B12 levels after long-term metformin prescription. The average B12 concentration was significantly lower in the metformin-exposed group vs. those without diabetes (439.2pg/dl vs. 522.4pg/dl; P=0.0015)

Also, about 7 percent of patients with diabetes receiving metformin were considered vitamin B12 deficient (less than 170pg/dl) vs. 3 percent of patients without diabetes or metformin exposure (P=0.001).

After adjusting for gender, race, ethnicity, body mass index, and number of years treated at the VAMC, patients using metformin were 2–3 times more likely not to be tested for vitamin B12 status vs. those not exposed to metformin based on their age.

Since metformin is first-line therapy for treating 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," concluded study author Vijaya Kancherla, PhD.