The impact of levothyroxine on thyroid antibody titers, thyrotropin, free thyroxine and free triiodothyronine is more pronounced in women with autoimmune subclinical hypothyroidism receiving metformin than myo-inositol.
Abstract
What is known and objective
Insulin resistance impairs the impact of levothyroxine on thyroid autoimmunity and hypothalamic–pituitary–thyroid axis activity. Both metformin and myo-inositol were found to improve insulin sensitivity and to reduce thyrotropin levels in individuals with hypothyroidism. The aim of the present study was to compare the effect of levothyroxine on thyroid autoimmunity and hypothalamic–pituitary–thyroid axis activity between women receiving metformin and myo-inositol.
Methods
The study included two groups of women with autoimmune hypothyroidism, treated for at least 6 months with either metformin (group A; n = 25) or myo-inositol (group B; n = 25). Both groups were matched for age, insulin sensitivity, hormone levels and antibody titers. For the following 6 months, all women received levothyroxine. Plasma levels of glucose, insulin, thyrotropin, free thyroid hormones, prolactin, 25-hydroxyvitamin D and high-sensitivity C-reactive protein (hsCRP), as well as titers of thyroid peroxidase and thyroglobulin antibodies were assessed at the beginning and at the end of the study.
Results and discussion
At baseline there were not differences between the study groups. Although levothyroxine reduced thyrotropin levels, increased free thyroid hormone levels and decreased antibody titers in both study groups, these effects were more pronounced in group A than group B. Only in group A, levothyroxine increased 25-hydroxyvitamin D, decreased hsCRP and improved insulin sensitivity. The impact of levothyroxine on thyrotropin and free thyroid hormones correlated with treatment-induced changes in insulin sensitivity, antibody titers, 25-hydroxyvitamin D and hsCRP.
What is new and conclusion
The present study suggests that the impact of levothyroxine on thyroid autoimmunity and hypothalamic–pituitary–thyroid axis activity is stronger in women receiving metformin than in women treated with myo-inositol.
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