Thyreotropin levels in diabetic patients on metformin treatment

ObjectiveA retrospective study to evaluate the changes in TSH concentrations in diabetic patients treated or not treated with metformin and/or l-thyroxine (l-T4).MethodsThree hundred and ninety three euthyroid diabetic patients were divided into three groups on the basis of metformin and/or l-T4 treatment: Group (M−/L−), 119 subjects never treated with metformin and l-T4; Group (M+/L−), 203 subjects who started metformin treatment at recruitment; and Group (M+/L+), 71 patients on l-T4 who started metformin recruitment.ResultsThe effect of metformin on serum TSH concentrations was analyzed in relation to the basal value of TSH (below 2.5 mIU/l (Q1) or between 2.51 and 4.5 mIU/l (Q2)). In patients of group M+/L+, TSH significantly decreased independently from the basal level (Q1, from 1.45±0.53 to 1.01±1.12 mU/l (P=0.037); Q2, from 3.60±0.53 to 1.91±0.89 mU/l (PP=0.004)); in M−/L− patients, no significant changes in TSH levels were observed. In patients of group M+/L− showing high-normal basal TSH levels, a significant decrease in TSH was observed independently from the presence or absence of thyroid peroxidase antibodies (AbTPO; Q2 AbTPO +: from 3.38±0.48 to 1.87±1.08 mU/l (PPConclusionsThese data strengthen the known TSH-lowering effect of metformin in diabetic patients on l-T4 treatment and shows a significant reduction of TSH also in euthyroid patients with higher baseline TSH levels independently from the presence of AbTPO.