Influence of metformin intake on serum vitamin B12 levels in patients with type 2 diabetes mellitus

OBJECTIVE: To describe the prevalence of vitamin B12 deficiency among Jordanian patients with type 2 diabetes mellitus treated with metformin and to compare the findings with those who did not receive metformin. DESIGN AND METHOD: Total 155 patients with type 2 diabetes mellitus, aged between 48 and 82 years were enrolled in the current study. They were divided into two groups; the first (n = 120) was treated with metformin while the second (n = 35) was not. Patients’ demographics (age, gender, duration of type 2 diabetes mellitus, smoking status), medication parameters (daily dosage and duration of metformin therapy), and biochemical parameters (hemoglobin level, mean corpuscular volume (MCV), serum vitamin B12, and folate level) were recorded. Definite deficiency was defined as serum vitamin B12 levels of < 150 pg/ml, whereas < 200 pg/ml indicated possible deficiency. RESULTS: The mean serum ± standard deviation (SD) vitamin B12 level was significantly lower in patients who were treated with metformin (268.5 ± 35.8 vs. 389.5 ± 29.8 pg/ml, p = 0.029). The metformin group had significantly higher prevalence of definite deficiency (32% vs. 9%, p < 0.02) and possible deficiency (48% vs. 30%, p < 0.02). Within the metformin group, the mean serum ± SD vitamin B12 level was significantly lower in those on high dosage (175.2 ± 30.5 vs. 315.6 ± 37.8 pg/ml, p < 0.001). MCV (μm(3)) levels ± SD were higher in the metformin group (87.5 ± 2.9 vs. 83.7 ± 2.4) with no statistical significance. CONCLUSION: There is a significant association between metformin intake and vitamin B12 deficiency. Serum vitamin B12 levels should be checked by physicians and serial monitoring is necessary in patients who are treated with metformin.