The Hidden Cost of Metformin: Deficiency of Vitamin B12 in Iraqi Patients with Type 2 Diabetes

Background: Metformin remains a cornerstone in the management of type 2 diabetes mellitus. However, extended use has been increasingly linked to vitamin B12 deficiency, contributing to neuropathy, anemia, and cognitive impairment. Objective: To assess the prevalence of vitamin B12 deficiency among Iraqi patients with type 2 diabetes mellitus receiving long-term metformin therapy and to identify associated clinical and demographic risk factors. Methods: This cross-sectional study enrolled 500 type 2 diabetes mellitus patients on metformin for ≥18 months. Serum vitamin B12 levels were measured using chemiluminescence immunoassay. Correlations with demographic and clinical variables (including smoking, hemoglobin, and fasting blood sugar were evaluated using Pearson’s correlation and multivariable regression analysis (SPSS v29). Results: Vitamin B12 deficiency (/mL) was identified in 19% of participants. Smoking, gender, and diabetes-related complications were significantly associated with lower B12 levels (p < 0.05). Fasting blood sugar demonstrated a strong negative correlation with B12 (r = –0.72, p < 0.001), while hemoglobin showed a weak positive correlation (r = 0.25, p = 0.04). Multivariable analysis confirmed that smoking and poor glycemic control were independent predictors of deficiency, after adjusting for age, gender, and comorbidities. Conclusion: Vitamin B12 deficiency is common among metformin-treated type 2 diabetes mellitus patients, especially in smokers and those with poor glycemic control. Routine screening and early nutritional intervention are recommended to mitigate associated complications.