Introduction: Subclinical hypothyroidism (SCH) seems to be associated with increase in cardiovascular risk factors and insulin resistance. The effect of the treatment of SCH with L-thyroxine on cardiovascular profile is not yet clear.

Methods: We evaluated the effects of L-thyroxine therapy in 120 patients (mean age 45.7 ± 12.2 years, 80 women) with SCH due to autoimmune thyroiditis that had no prior treatment for thyroid or cardiovascular disease. The treatment was titrated to TSH levels between 0.4 and 4.0mIU/L. The laboratory data obtained, before and at least 6 months after thyroid function normalization, included thyroid function, antithyroid antibodies, lipid profile, and HOMA-IR (Homeostasis Model Assessment for insulin resistance), HISI (Hepatic Insulin Sensitivity Index), and IGI (Insulinogenic Index). Statistical analysis was performed with Mann-Whitney test, and Spearman’s correlation coefficient.

Results: After treatment L-thyroxine, we observed a significant decrease of TSH (6.43±0.53 to 1.23±0.42 mIU/L, p=0.03) and a significant increase of fT4 (0.74±0.12 to 1.25±0.14 ng/mL, p<0.05). We also observed a decrease of LDL (116.1±34.2 to 91.2±16.3 mg/dL, p<0.01) and Lp(a) (32.0 ±19.1 mg/dL to 21.4±18.1 mg/dl, p<0,01). HDL and Apo A1 increased significantly after treatment (45.2±15.2 to 58.5±18.1 mg/dL, p <0.01; 124.5±43.3 vs. 136.5±56.4 mg/dL, p<0.01, respectively). Treatment with L-thyroxine significantly reduced HOMA-IR (0.24±0.17 to 0.17±0.10, p=0.03) and HISI (334.9±92.9 to 703.8±97.1, p=0.02). At baseline, TSH was positively correlated with total cholesterol (r=0.38, p=0.01), LDL (r=0.38, p=0.01), TG (r=0.28, p=0.01) and IGI (r=0.22, p=0.05). FT3 was negatively correlated with Lp(a) (r =-0.41, p=0.04).

Conclusions: The treatment of SCH in patients with autoimmune thyroiditis is associated with a significant improvement of insulin resistance and cardiovascular risk.


C. Neves: None. S.C. Oliveira: None. J. Neves: None. M.G. Pereira: None. O. Sokhatska: None. A. Oliveira: None. J. Medina: None. L. Delgado: None. D.M. Carvalho: None.

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