The Relationship Between Thyroid Hormone Levels, Insulin Resistance and Body Mass Index, in Patients with Subclinical Hypothyroidism and Euthyroid Patients

Background. Hypothyroidism is a common thyroid disorder with female predominance. In general population its prevalance is 2–5% while 10 times higher in female than in men. Insulin resistance, one of the most discussed issues recently, is an inadequate response to insulin in peripheral tissues despite the normal secretory function of pancreatic islet cells. In this study, we analyzed relationship between thyroid hormone levels, body mass index and insulin resistance calculated with Homeostatic Model Assessment for Insulin Resistance (HOMA-IR), Quantitative Insulin Sensitivity Check Index (QUICKI) and Atherogenic Index of Plasma (AIP) in SCH and euthyroid patients under levothyroxine treatment. Materials and methods. The clinical and laboratory data of approximately 14000 patients between the ages of 18–60 were retrospectively evaluated. After these exclusion criteria were applied, 371 eligible individuals were included in the study. All 371 individuals divided into three groups according to TSH levels. Group 1 is eutyhroid patients under levothyroxine treatment with TSH levels between 0.27–4.2μIU/mL. Group 2 is subclinical hypothyroid patients with TSH levels between 4.2–10 μIU/mL. Group 3 is healthy control group with TSH levels between 0.27–4.2 μIU/mL. Results. The euthyroid patient group has the highest (25.66±3.36 kg/m2) mean BMI. On the other hand the mean BMI was higher in SCH (24.0400±3.8436kg/m2) group than in control group (22.48±2.74 kg/m2) (p<0.05). Fasting plasma glucose (FPG), serum triglyserid, low density lipoprotein (LDL), anti-thyroid peroxidase (TPO) and insulin levels were significantly higher in euthyroid patient and SCH groups (p<0.05). Notably, total cholesterol, LDL and TPO levels were higher in euthyroid patient group (p<0.05). On the other hand, there were no difference between euthyroid patients and SCH group. Conclusions. This study found significantly elevated insulin resistance and cholesterol levels in SCH patients, so we hypothesized that SCH is also a risk factor for insulin resistance disorders such as cardiovascular diseases and metabolic syndrome. As a consequence, lipid metabolism defects and insulin resistance should be screened and treated in SCH patients. Thanks to the strong and significant correlation between HOMA and QUICKI in our study, we suggest the combined use of HOMA and QUICKI in these patients. Further and large-scale studies are needed to evaluate the relationship of HOMA, QUICKI, AIP, and BMI in detecting insulin resistance in SCH patients.