Objective: To determine the effect of metformin on the levels of plasma homocysteine (Hcy), serum vitamin B12 and folic acid in patients with type 2 diabetes mellitus and the relationship between cumulative metformin exposure and levels of plasma homocysteine (Hcy).
Material and method: The cross sectional study was conducted to assess the effect of metformin treatment on plasma homocysteine (Hcy), serum vitamin B12 and folic acid in 152 type 2 diabetic out-patients aged between 35-65 years old at the Diabetes Clinic of The Makaruk Hospital, Kanchanaburi, Thailand Among those, 88 and 64 patients were categorised to the metformin and non-metformin group according to their records of receiving metformin treatment for a period of a minimal 6 consecutive months before the study. Fasting blood was drawn from each patient and analysed for plasma homocysteine using the Fluorescence Polarization Immunoassay (FPIA) method (IMX Analyzer), and serum vitamin B12 and folic acid using the radioimmunoassay method
Results: The plasma Hcy levels showed no significant difference (p = 0.544) among patients in the metformin group compared with those in the non-metformin group (10.6+/-5.8 mol/L vs 10.4+/-4.0 mol/L). There was a significant difference (p = 0.011) in the levels of serum vitamin B12 among patients in the metformin group and among those in the non-metformin group (318.0+/-192.2 pg/mL vs 434.3+/-300.7 pg/mL). However, there was no significant difference (p = 0.090) in serum folic acid levels between patients in the metformin and those in the non-metformin group (8.8+/-5.1 ng/mL vs 7.7+/-3.8 ng/mL). The plasma Hcy levels showed a significant correlation with the duration of metformin treatment (p = 0.014) and the amount of metformin received (p = 0.015) with the Spearman correlation coefficient of 0.260 and 0.258 respectively.
Conclusion: Even though the direct effect of metformin treatment on the plasma Hcy could not be concluded from the present study, it was found that there was a significant depletion of level of serum vitamin B12 among patients who had been on long-term metformin treatment. Therefore, vitamin B12 supplement is suggested for diabetic patients who are receiving metformin medication.