Methods: This was a cross-sectional study. A randomized list of patients with type 2 DM treated with metformin who attended a general out-patient clinic from 1st December 2019 to 29th February 2020 was generated. Both serum total and active vitamin B12 levels would be checked and either one below the cut-off values would be defined as vitamin B12 deficiency.

Results: A total of 406 patients were recruited. The prevalence of metformin induced vitamin B12 deficiency was 22.4%. Higher metformin dosage was found to be a statistically significant associated factor for developing vitamin B12 deficiency. Compared with metformin dosage of less than 1000mg/day, the OR of developing vitamin B12 deficiency for 1500mg to less than 2000mg/day was 3.71 (95% C.I.: 1.10 to 12.54; p=0.04); and for 2000mg/day or above was 8.03 (95% C.I.: 2.76 to 23.34; p<0.01). Among the patients with metformin induced vitamin B12 deficiency, 23.1% of patients had anemia and only 9.9% had macrocytosis. Longer duration of diabetes, longer duration of use of metformin, diabetic control and the use of proton pump inhibitor (PPI) were not associated with vitamin B12 deficiency.

Conclusion: Patients taking high dose of metformin (≥1500mg/day) should be screened for vitamin B12 deficiency periodically in primary care even if they had no anaemia or macrocytosis.