Effects of Metformin on Thyroid Function in Patients of Subclinical Hypothyroidism

Abstract

Background : To study the effect of metformin on thyroid function test (TFT) in patients of subclinical hypothyroidism (SCH). Methods: A total of 30 patients of SCH with TSH between 5 - 10 mIU/L were given 2, 000 mg/day of metformin for12 weeks. Patients were divided into two groups based on presence or absence of thyroid peroxidase antibody (TPO). Baseline anthropometric characteristics, fT3, fT4, TSH, serum insulin, HOMA-IR and quality of life were assessed at baseline and at 12 weeks. Results: A total of 23 patients (76.7%) who were TPO antibody negative (group 1) showed statistically significant decrease in TSH concentration at 12 weeks with no significant change in fT3 and fT4 in contrast to 7 patients (23.3%) who were TPO antibody positive (group 2). Patients in group 1 were significantly more obese, had higher serum insulin and HOMA-IR as compared to group 2. Body weight, waist circumference, BMI and percentage body fat decreases significantly in both the groups at 12 weeks as compared to baseline but on intergroup comparison this decrease was not significant statistically (P = 0.46). The HOMA-IR of group 1 was significantly higher than that of group 2 at baseline (P ? 0.02). Serum insulin and HOMA-IR decreased significantly in both the groups but again on intergroup comparison, no significant difference was observed. A positive correlation between serum TSH and serum insulin level and HOMA-IR level (r = 0.608, P ? 0.01 and r = 0.592, P ? 0.01 respectively) was observed in group 1. Conclusion: Metformin suppresses serum TSH levels without affecting fT3 and fT4 levels in SCH without any evidence of autoimmune thyroiditis. doi: http://dx.doi.org/10.4021/j em188 w