Insulin Resistance in Relation to Hyperthyroidism and Hypothyroidism

Thyroid hormones (TH) play an important role in regulating energy balance, metabolism of glucose, and lipids. While TH oppose the action of insulin and stimulate the hepatic gluconeogenesis and glycogenolysis they up-regulate the expression of genes such as glucose transporter type-4 (GLUT--4) and phosphoglycerate kinase, involved in glucose transport and glycolysis, respectively, thus acting synergistically with insulin facilitating glucose disposal and utilization in peripheral tissues.

This indicates a possible interplay between thyroid status and insulin sensitivity. Homeostatic model assessment (HOMA) is a method for assessing β-cell function and insulin resistance (IR) from basal (fasting) glucose and insulin or C-peptide concentrations. The homeostasis model assessment (HOMA) for IR (HOMA-IR) derives estimates of insulin sensitivity from the mathematical modeling of fasting plasma glucose and insulin concentrations.

Homeostatic model assessment for insulin resistance (HOMA - IR) based on fasting glucose and insulin measurements; derived from the product of the insulin and glucose values divided by a constant, that is, calculated by using the following formula: fasting glucose (mg/dL) X fasting insulin (mU/L) / 405 (for SI units: fasting glucose (mmol/L) X fasting insulin (mU/L) / 22.5) , a value greater than 2 indicates insulin resistance .

In both hyper- as well as hypothyroid groups, there was significant increase in LDL levels. The amount of insulin specifically bound and the number of insulin receptors per cell were inversely correlated with the LDL level. The number of insulin receptors and the amount of insulin bound in the tested subjects with increased LDL were correspondingly low.