Effects of metformin or rosiglitazone on serum concentrations of homocysteine, folate, and vitamin B12 in patients with type 2 diabetes mellitus

ObjectivesMetformin is widely used in patients with type 2 diabetes but may decrease vitamin B12 levels and increase levels of homocysteine (Hcy), a cardiovascular risk factor. Rosiglitazone, a peroxisome proliferator-activated receptor-γ agonist, may reduce markers of inflammation. We investigated whether 6 weeks' treatment with metformin or rosiglitazone affects serum concentrations of Hcy, folate, or vitamin B12 in subjects with newly diagnosed type 2 diabetes compared with controls.MethodsWe examined 165 patients with type 2 diabetes. Fasting blood samples, a physical examination, and a complete medical history were performed at the beginning and at the end of the treatment. All blood samples were obtained after a 12-h fast.ResultsAfter treatment, metformin use was associated with an increase in levels of Hcy by 2.36 μmol/l and decreases in folate and vitamin B12 concentrations by −1.04 ng/ml and −20.17 pg/ml. During rosiglitazone treatment, Hcy levels decreased by −0.92 μmol/l; folate and vitamin B12 levels remained unchanged. Metformin and rosiglitazone significantly decreased levels of triglyceride (TG), low-density lipoprotein (LDL), total cholesterol (total-C), HbA1c, insulin, and homeostasis model assessment (HOMA). Metformin also significantly decreased body weight. In controls, there was no change in Hcy, folic acid, vitamin B12, TG, LDL, total-C, HbA1c, insulin, or HOMA levels. Homocysteine change did not correlate with insulin, folate, or vitamin B12 changes in the metformin and rosiglitazone groups.ConclusionsIn patients with type 2 diabetes, metformin reduces levels of folate and vitamin B12 and increases Hcy. Conversely, rosiglitazone decreases Hcy levels in this time period. The clinical significance of these findings remains to be investigated.