Effect of metformin therapy on the development of vitamin B12 deficiency in patients with type 2 diabetes mellitus

Introduction . For the past decades, metformin has been the drug of choice for the treatment of patients with type 2 diabetes mellitus (T2DM). However, its long-term use leads to a number of side effects, such as the development of vitamin B12 deficiency (VB12). Aim . Assess the safety of metformin use in real clinical practice in the treatment of patients with type 2 diabetes based on the analysis of the incidence of VB12 deficiency. Materials and methods . Sixty patients with T2DM aged 27 to 65 years were examined in a city polyclinic. The average anamnestic duration of T2DM was 68 [4; 291] months. All patients were on selected hypoglycemic therapy: 19 patients (31.7%) received metformin monotherapy, and 41 patients (68.3%) received metformin as part of combination therapy. The average duration of metformin therapy was 62 [3; 291] months. All patients underwent analysis of the VB12 content in the blood serum depending on the duration of metformin intake. Results . The average VB12 level in the examined patients was 345 [99; 770] pg/ml. Normal VB12 levels were observed in 51 (85%) patients (386 [221; 770] pg/ml), VB12 deficiency (<200 pg/ml) was detected in 9 (15%) patients (146 [99; 195] pg/ml), the differences between VB12 levels were significant (p < 0.05). At the same time, in 37 (61.7%) patients with normal VB12 levels, its values were assessed as borderline (in the range of 200–450 pg/ml), and amounted to 335 [221; 470] pg/ml. VB12 deficiency developed more often in patients taking metformin for more than 1 year (16.7%), borderline VB12 levels were more often found in patients taking metformin for less than a year (58.3%) and more than 5 years (71%). However, the dependence of VB12 levels on the duration of metformin intake was not significant (p > 0.05). Conclusion . Metformin use results in the development of VB12 deficiency in every sixth patient with T2DM, primarily after one year of treatment.