Association between thyroid hormone levels and insulin resistance and body mass index

OBJECTIVE Previous studies have shown an association between thyroid function and insulin resistance and obesity. We compared insulin resistance and body mass index (BMI) in patients with normal TSH levels (2.5-4.2 µIU/mL), patients diagnosed with subclinical hypothyroidism, and healthy control subjects. METHODS The study included 104 subjects and was conducted at the Taksim Education and Research Hospital. The subjects were divided into three groups according to TSH levels: Group 1 (high-normal), TSH levels were 2.5-4.2 µIU/mL (n=33); Group 2 (subclinical hypothyroidism), TSH levels were 4.2-10 µIU/mL (n=42); and Group 3 (healthy control), TSH levels were 0.27-2.5 µIU/mL (n=29). The fT3 and fT4 levels were within normal limits in all groups. Insulin resistance and BMI were compared among groups. The homeostasis model assessment of insulin resistance (HOMA-IR) was used to estimate insulin resistance. RESULTS HOMA-IR and BMI were not significantly different among groups (p>0.05). A significant positive correlation was found between BMI and HOMA-IR in the high-normal TSH (p>0.059) and subclinical hypothyroidism (p>0.05) groups. CONCLUSIONS HOMA-IR and BMI are important for the assessment of diabetes and cardiovascular diseases. We found no significant difference in HOMA-IR and BMI values among the three TSH reference range groups.