The Role of Metformin on Serum Vitamin B12 Levels in Patients with Type 2 Diabetes Mellitus

Objective. To evaluate the vitamin B12 (VB12) deficiency in patients with type-2 diabetes mellitus (DM-2) using metformin or other hypoglycemic agents. Methods. 400 patients with DM-2 were divided into two arms (N=200/group); 1) those receiving metformin (MET) for at least six months and 2) those receiving hypoglycemic agents other than metformin (OHA). Serum VB12 concentrations were measured. Data were analyzed by using two-sample t-test for numerical data and chi-square with logistic regression analysis for categorical data. Numerical values were expressed as means ± standard deviations. Null hypotheses were rejected at P-values <0.05. Results. Definite biochemical VB12 deficiency (<148 pmol/L) was found in 29/200 (14.5%) of the MET group while it was observed in 4/200 (2%) in the OHA group (P<0.001). Similarly, possible VB12 deficiency (serum concentrations <185 pmol/L) was found in 39 (19.2%) of the MET group and 12 (6%) in the OHA group (p<0.001). There was positive correlation between low VB12 level and metformin administration (R2=0.26, p<0.001). Conclusion. Patients with DM-2 on metformin had lower VB12 levels than those on other hypoglycemic drugs. The relation between VB12 deficiency and metformin therapy indicates the need for periodic measurement of serum VB12 levels in patients treated with metformin.