Metformin (brand names Glucophage, Glucophage XR, Fortamet, Riomet, Glumetza, and others) is a popular and highly effective oral diabetes drug used to help manage Type 2 diabetes. This drug works by lowering the amount of glucose made by the liver and by making the body's cells more sensitive to insulin.

 

Taking metformin increased the chances of developing vitamin B12 deficiency, according to a new study of type 2 diabetics on insulin. The Dutch trial randomized 390 patients to receive either 850 mg of metformin or a placebo three times a day for 4.3 years. Their levels of vitamin B12, folate and homocysteine were measured at baseline and 4, 17, 30, 43 and 52 months.

 

The metformin group showed a persistent, progressive decrease in B12 concentrations, with a mean decrease of 19% compared to the placebo group. At the end of the study, patients taking metformin were 7% more likely to be B12-deficient (less than 150 pmol/L) and 11% more likely to have a low level (15 to 220 pmol/L). The metformin patients also had lower folate concentrations than placebo recipients, although both groups showed an overall increase and the difference between groups was eliminated after adjustments for body mass index and smoking.

 

There was also an increase in homocysteine levels in the metformin group that was not statistically significant across the whole group, but showed that patients who were B12-deficient had higher concentrations of homocysteine (a mean of 23.7 µmol/L compared to 14.9 µmol/L in patients with normal B12 levels). The study was published online by BMJ.

 

Based on the findings, study authors concluded that regular measurement of B12 concentrations should be considered for patients on long-term metformin treatment. They noted that deficiencies are relatively easy and cheap to treat effectively and safely.