Thyroid Antibody Titers and Hypothalamic-Pituitary-Thyroid Axis Activity in Levothyroxine-Treated Women With Autoimmune Subclinical Hypothyroidism Receiving Atorvastatin or Metformin

Abstract

Both metformin and statins reduce thyroid antibody titers in individuals with Hashimoto thyroiditis. The present study compared the impact of low-grade systemic inflammation and insulin resistance on levothyroxine action in subjects with this disorder. The study included 3 groups of women with autoimmune subclinical hypothyroidism matched for thyroid antibody titers and hormone levels: patients receiving atorvastatin (group A) or metformin (group B) and statin- and metformin-naïve women (group C). Over the entire study period (6 months), all individuals received levothyroxine. Titers of thyroid antibodies, as well as concentrations of thyrotropin, free thyroid hormones, prolactin, lipids, glucose, insulin, high-sensitivity C-reactive protein (hsCRP), and 25-hydroxyvitamin D were assessed at baseline and 6 months later. At baseline, the study groups differed in plasma lipids, insulin sensitivity, and hsCRP. In all groups of patients, levothyroxine decreased thyroid antibody titers, reduced thyrotropin levels and increased free thyroid hormone levels. Treatment-induced changes in antibody titers and free thyroid hormone levels were strongest in group A, while the changes in thyrotropin were most pronounced in group B. The decrease in antibody titers correlated to a greater degree with hsCRP levels than with insulin sensitivity. The obtained results suggest that low-grade systemic inflammation is a more important factor determining the impact of levothyroxine on thyroid autoimmunity and thyroid hormone levels than insulin resistance.

Keywords: insulin resistance; low-grade systemic inflammation; metformin; statins; supplemental therapy; thyroid autoimmunity; thyroid hypofunction.