Serum Vitamin B12 Levels in Type 2 Diabetes Patients on Metformin Compared to those Never on Metformin: A Cross-sectional Study

CONTEXT: There are limited data about the effect of metformin use on serum Vitamin B12 levels in type 2 diabetes patients from India. AIMS: We studied serum Vitamin B12 levels in patients with type 2 diabetes mellitus who were receiving metformin and compared them to those never treated with metformin. SUBJECTS AND METHODS: A total of 183 patients (“metformin” group 121, “no metformin” group 63) of type 2 diabetes from the endocrinology clinic of a tertiary care center in North India were studied. Serum Vitamin B12 levels were measured in all patients. Diabetic neuropathy symptom score (DNS) and diabetic neuropathy examination score (DNE) were used to assess peripheral neuropathy while hemoglobin and mean corpuscular volume (MCV) were used to assess anemia. RESULTS: The serum Vitamin B12 levels were 267.7 ± 194.4 pmol/l in metformin group and 275.1 ± 197.2 pmol/l in the no metformin group (P = 0.78). When adjusted for duration of diabetes, metformin use was associated with a 87.7 ± 37.7 pmol/l (95% confidence interval [CI], −162.1–−3.3, P = 0.02) lower serum Vitamin B12 levels. No significant increase in the prevalence of neuropathy (DNS and DNE scores), anemia, or MCV was found in the Vitamin B12 deficient patients (levels <150 pmol/l) as compared to patients with normal Vitamin B12. However, serum Vitamin B12 levels for the entire cohort were higher by 12.2 ± 3.0 pmol/l (95% CI 6.4–18.0, P < 0.001) for every 1 year increase in the duration of diabetes. CONCLUSIONS: Metformin use was associated with a lower serum Vitamin B12 levels when adjusted for duration of diabetes. Increasing duration of diabetes was associated with higher serum Vitamin B12 levels.