Effect of metformin on thyroid function tests in type 2 diabetic patients

Background: Diabetes mellitus (DM) and thyroid disorder appears to be closely related.It has long been recognised that thyroid hormones have marked effects on glucose homeostasis, and although autoimmune thyroid disease is more prevalent in type 1 diabetes as a result of their common origin, in patients with type 2 diabetes the prevalence of hypothyroidism and hyperthyroidism is similar to that of the general population. The present study was conducted to assess the interplay between metformin treatment and thyroid function in type 2 diabetic patients. Methods: A total of 73 diabetic patients were enrolled in this study, they were divided into two groups, the first group included 37 type 2 diabetic patients on metformin therapy, whereas the second group involved 36 type 1 diabetic patients on insulin therapy. Another group involved 35 apparently healthy volunteers were also included in the study as a control group. Blood samples were taken from the patients and controls, then the serum was analyzed for measurement of fasting serum glucose (FSG), total T3, free T3 (FT3), total T4, freeT4 FT4) and TSH using ELFA (Enzyme Linked Fluorescent Assay) technique (minividas). Results: the results showed that there were no significant differences between T3, FT3, FT4 and TSH of the metformin group when compared to the same parameters in the control group. On the other hand FT3 and FT4 of insulin group were significantly lower than that of the control and metformin groups. Also total T4 inmetformin and insulin groups was significantly lower than that of control group, whereas the TSH of insulin group was significantly higher than that of control and metformin groups. Conclusion:Chronic use of metformin in type 2 diabetic patients has no effects on thyroid function tests, and there was no significant correlation between glycemic control and thyroid hormones or TSH. However, TSH, T4, FT3 and FT4 in insulin group were significantly differe from control group and this may indicate the presence of subclinical hypothyroidism.