Study of Insulin Resistance in Subclinical Hypothyroidism

Thyroid hormones influences glucose homeostasis. The association of insulin resistance in overt hypothyroidism is well proven, but very less information is available about insulin action on subclinical hypothyroidism. This study was done to evaluate the association between thyroid hormones and insulin resistance in subclinical hypothyroidism (SCH). Thirty subjects diagnosed as SCH and 30 age matched euthyroids were included. Serum TSH, FT3, FT4, fasting plasma glucose and insulin were estimated. Homeostasis Model Assessment was used to assess insulin resistance (HOMA- IR). Serum TSH levels were significantly increased in SCH (14.20 ± 5.23 μU/ml) when compared with euthyroids (2.24 ±1.43μU/ml; P< 0.0001). Serum FT3, FT4 levels in SCH (2.96±0.80 pg/ml & 1.15 ± 0.52 ng/dl) were within the normal range. The mean insulin levels were significantly elevated in SCH (9.07±3.41 μU/ml) when compared with euthyroids (5.28± 2.18 μU/ml; P-value < 0.0001). The mean HOMA IR was significantly elevated in SCH (2.03 ± 0.95) when compared with euthyroids (1.05±0.45, P-value < 0.0001). TSH levels positively and moderately correlated with insulin (r= 0.43 P=0.03) and HOMA IR (r =0.48; P= 0.01). FT3 levels negatively and strongly correlated with insulin (r= -0.5, P=0.004) and moderately with HOMA IR (r= -0.38, P= 0.04). FT4 levels negatively and weakly correlated with insulin and IR (r= - 0.11, P=0.54; r= - 0.07, P=0.69 respectively). To conclude, SCH is associated with insulin resistance. Hence there is an increased risk of insulin resistance associated disorders such as metabolic syndrome, cardiovascular events in SCH.