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.