[Are the thyroid hormones and thyrotropin associated with cardiometabolic risks and insulin resistance even in euthyroid subjects?]

Associations of both hypothyroidism and subclinical hypothyroidism with metabolic syndrome are well established. Nowadays, more attention has been paid to the role of thyroid hormones and thyrotropin (TSH) within the euthyroid range on the development of cardiometabolic health risks. The paper summarizes current knowledge related to the associations of lower free thyroxine (fT4) level and higher levels of both free triiodothyronine (fT3) and TSH with body adiposity, metabolic syndrome and insulin resistance in euthyroid subjects. In our recent study of obese euthyroid adolescents, we revealed that fasting insulin and homeostasis model assessment of insulin resistance (HOMA-IR) positively correlated with fT3 and TSH and negatively with fT4. The ratio of fT3 to fT4 was also significantly related to HOMA-IR both in girls (r = 0.347, p < 0.001) and boys (r = 0.267, p < 0.001). It is concluded that up-to-date conducted studies mostly confirmed that thyroid hormones and TSH even in euthyroid range may significantly affect the metabolic health and particularly insulin sensitivity.Key words: euthyroid range - insulin resistance - metabolic health - metabolic syndrome - obesity - thyrotropin - thyroxine - triiodothyronine.