Vitamin B12 status of patients treated with metformin: a cross-sectional cohort study

Abstract

Aim To assess the vitamin B12 status of patients with type 2diabetes who had been receiving metformin treatment for at least one year. Methods Patients with type 2 diabetes attending a diabetes clinic were included in a cross-sectional cohort study. Patients exposed to metformin for more than one year (n=53) were compared with a non-exposed control group (n=31). Serum cobalamin and other variables reflecting vitamin B12 status were measured. Results Patients on metformin had lower cobalamin (289±137 vs. 395±162 pmol/L; p<0.01) and holotranscobalamin (76±49 vs. 97±41 pmol/L; p<0.05), and higher HCy (11.3+3.3 vs. 10.3±2.3 µmol/L; p<0.05); these changes were correlated. Eight metformin patients, but no controls, had holotranscobalamin below the normal range (p<0.05). Methylmalonic acid and folate were similar in both groups. Conclusion Patients exposed to long-term metformin therapy had 26.7% lower cobalamin, 21.6% lower holotranscobalamin and 9.7% higher HCy serum concentrations than control subjects. Such changes indicate a potential risk for development of vitamin B12 deficiency. Our results highlight the necessity of checking B12 status during metformin therapy.