To Determine Vitamin B12 Deficiency in Type 2 Diabetes Mellitus Patients on Metformin Therapy

India harbors the second-largest population with diabetes, with over 100 million, and type 2 diabetes mellitus (T2DM) constitutes the major share. Metformin remains the first-line pharmacotherapy for T2DM due to its safety profile, cost-effectiveness, and beneficial metabolic effects.

The aim of the study was to assess the frequency of vitamin B12 deficiency in patients with T2DM on metformin therapy and compare it with their cohabiting family members who are not on metformin but share similar dietary habits.

This study included 180 participants with 90 cases and controls each, and we enrolled 89 females (49.4%) and 91 males (50.6%). The mean age was 57 (± 4.88) years, and overall gender distribution and dietary pattern were nearly balanced among cases and controls. The mean duration of diabetes among cases was 7.69 ± 4.35 years, and duration of metformin use was 5.22 ± 3.77 years, ranging from 1-16 years. The mean daily dose of metformin was 1238.89 ± 586.50 mg/day, with a median dose of 1000 mg/day. The mean serum vitamin B12 level in metformin users was significantly lower than in controls (206.66 ± 59.09 pg/mL vs 301.44 ± 72.28 pg/mL, p < 0.001). Vitamin B12 deficiency was present in 40.0% of metformin users versus 11.1% of controls, yielding an odds ratio of 5.33 (95% CI: 2.44-11.65), which was a highly significant difference between the two groups (t = -9.631, p < 0.001), strongly suggesting an association between metformin use and reduced B12 levels. Neurological symptoms were observed in 14.4% of cases (OR 4.896, 95% CI: 1.345-17.827; p = 0.009).

Long-term metformin use in T2DM patients is strongly associated with both biochemical vitamin B12 deficiency and an increased likelihood of neurological symptoms.