Endocrine Abstracts

Aim: Thyroid hormones act both insulin agonistic and antagonistic in different organs. Studies that evaluate the relationship between insulin resistance and hypo-hyperthyroidism have conflicting results, even euthyroid status was shown to change insulin sensitivity. In this study, our aim is to investigate the association between TSH, free T₄, free T₃ levels and insulin resistance in euthyroid patients.

Method: Euthyroid 57 males, 47 females total 104 patients were involved to study, patients that use any drug that affects thyroid, insulin and glucose levels and have any chronic disease, thyroid disease and obesity were excluded. BMI, fasting glucose levels, insulin levels, lipid profiles of patients were evaluated. Insulin resistance was measured with homeostasis model assessment (HOMA-IR), carotis intima media thickness (CIMT) were measured. Patients were classified as two groups due to TSH levels, the patients with TSH levels below 2 mIU/l were defined as group 1 and patients with TSH levels above 2 mIU/l were defined as group 2. Two groups were compared and correlation analysis were made.

Findings: There was not any significant difference between groups in terms of age, BMI (P>0.05). Fasting blood glucose, triglyceride and LDL levels were higher in group 2 but difference was statistically insignificant. Fasting insulin levels and insulin resistance that measured with HOMA-IR method were higher in group 2 when compared with group 1 and these findings were statistically significant (HOMA-IR in group 1; 0.80±0.51, in group 2; 1.63±1.70, fasting insulin levels in group 1; 3.83±2.23, in group 2; 7.56±7.54) (P=0.003). There was an positive correlation between TSH levels and HOMA-IR, CIMT (r: 0.46, P<0.001 and r: 0.37, P<0.001).

Discussion: Our study revealed that even in euthyroid patients normal TSH levels may be related to insulin resistance and an arteriosclerosis indicator CIMT. As TSH values exceeding 2 mIU/l, insulin resistance develops and due to relationship between insulin resistance and aterosclerosis carotis intima media thickness increases as well.These results raise questions whether current normal TSH levels are actually normal? And should it be narrower? To answer these questions more detailed studies with euthyroid population are required.