INSULIN RESISTANCE ACCOMPANIES TSH RESISTANCE IN OBESE

Background and Objectives: Obesity is associated with various endocrinal and non endocrinal disorders. One major endocrine disorder associated with obesity is insulin resistance, due to defect in post receptor signal transduction in target tissue. Also obesity causes increase in thyroid stimulating hormone (TSH) with no effect or increase in triiodothyronin (T3), and no effect on thyroxin (T4). On the other hand, subclinical hypothyroidism causes obesity due to slow metabolism. Thus thyroid function tests and insulin resistance were evaluated to know whether TSH increase is a cause or consequence of obesity. Methods: 50 obese cases (body mass index > 30 kg/m2) [group I] were taken against 25 non obese controls (body mass index < 25kg/m2) [group II]. Blood sugar, insulin, T3, T4, TSH levels were measured. Blood sugar was estimated by glucose oxidase-peroxidase method while insulin, TSH, T3, T4 were done using respective radioimmunoassay kits. Homeostasis model for insulin resistance (HOMA IR) was calculated and cases were divided into insulin resistant [subgroup IA] and insulin non-resistant [subgroup IB] based on standardised value (mean+2 S.D.) of HOMA IR of controls [group II] which was taken as reference value to define the insulin resistance. Results: TSH was significantly increased in insulin resistant than in non resistant, whereas T3 and T4 levels were comparable. Conclusion: Raised TSH levels along with comparable and normal T3 and T4 in obese persons with insulin resistance could be due to association of thyroid receptor resistance to TSH similar to insulin resistance.