Metformin-associated vitamin B12 deficiency in the elderly

Objective. To compare the prevalence of the vitamin B12 deficiency in geriatric diabetic patients treated with or without metformin. Methods. Records of 134 patients with diabetes mellitus (DM) aged 61 to 93 (mean, 80) years who were treated with (n=56) or without (n=78) metformin were reviewed. Patient demographics (age, gender, duration of DM, smoking status, alcohol consumption), medication parameters (daily dosage and duration of metformin therapy), and haematological parameters (haemoglobin level, mean corpuscular volume [both of which may reflect vitamin B12 deficiency], serum vitamin B12, and folate level) were recorded. Definite deficiency was defined as serum vitamin B12 level of <150 pmol/L, whereas possible deficiency as <220 pmol/L. Results. The mean serum vitamin B12 level was lower in the metformin group (282.1 vs. 380.1 pmol/L, p=0.023). 15% and 37% of these patients had definite and possible vitamin B12 deficiency, respectively. The metformin group had significantly higher prevalence of definite deficiency (29% vs. 5%, p<0.001) and possible deficiency (52% vs. 27%, p<0.03). Odds ratios of definite and possible deficiency in the metformin group were 7.40 (95% CI, 2.32-23.62; p=0.001) and 2.92 (95% CI, 1.41-6.02; p=0.004), respectively. Within the metformin group, the mean serum vitamin B12 level was significantly lower in those on high dosage (173 vs. 315 pmol/L, p<0.005). Conclusion. Metformin use was significantly associated with vitamin B12 deficiency. Physician should check the patient’s baseline vitamin B12 level, and serially monitor vitamin B12 levels and nutritional status of those treated with metformin, and prescribe vitamin B12 supplement if necessary.