title: Association between thyroid hormones, thyroid antibodies and insulin resistance in euthyroid individuals: A population-based cohort.
abstract: OBJECTIVE
  The association between insulin resistance and thyroid function in euthyroid subjects has not yet been clarified. This study aimed to investigate the association between thyroid function within the normal reference range and insulin resistance in participants of the Tehran Thyroid Study (TTS).
  
  
  METHODS
  This cross-sectional study was conducted within the framework of the TTS. Of 5786 subjects aged ≥ 20 years, 2758 euthyroid subjects free of thyroid disorders, diabetes, chronic kidney disease and cardiovascular disease, and not taking steroids and lipid-lowering agents, were included. Serum concentrations of free thyroxine (FT4) and TSH were measured. The homoeostasis model assessment index for insulin resistance (HOMA-IR) was used to evaluate IR.
  
  
  RESULTS
  On linear regression analysis, a negative association was found between serum FT4 levels and HOMA-IR in the model with age, smoking and physical activity (B = -0.09, P < 0.001) and in the WC-adjusted model with age, smoking and physical activity for men (B = -0.06, P < 0.01). In addition, there was a positive association between serum TSH levels and HOMA-IR in both models [with age, smoking and physical activity (B = 0.07, P = 0.006), and age, smoking, physical activity and adjusted for WC (B = 0.05, P = 0.01)] that was not more significant on logistic regression analysis. In women, neither serum FT4 nor TSH levels were associated with HOMA-IR; the prevalence of IR decreased from 27.2 to 19.1 with increasing tertiles of FT4 only in men (P = 0.01). No significant differences were observed in HOMA-IR and its components between thyroid peroxidase antibody (TPOAb)-negative and -positive groups. Also, it was found that metabolically healthy but obese (MHO) subjects had higher levels of TSH than individuals who were MONW (metabolically obese but normal weight; P < 0.01).
  
  
  CONCLUSIONS
  Low FT4 was independently associated with IR in healthy euthyroid Iranian men.
authors.affiliation: Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, P.O. Box 19395-4763, Tehran, Islamic Republic of Iran.
authors.forename: A
authors.initials: A
authors.lastname: Amouzegar
authors.affiliation: Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, P.O. Box 19395-4763, Tehran, Islamic Republic of Iran.
authors.forename: E
authors.initials: E
authors.lastname: Kazemian
authors.affiliation: Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, P.O. Box 19395-4763, Tehran, Islamic Republic of Iran; Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Islamic Republic of Iran.
authors.forename: S
authors.initials: S
authors.lastname: Gharibzadeh
authors.affiliation: Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, P.O. Box 19395-4763, Tehran, Islamic Republic of Iran.
authors.forename: L
authors.initials: L
authors.lastname: Mehran
authors.affiliation: Prevention of Metabolic Disorders Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Islamic Republic of Iran.
authors.forename: M
authors.initials: M
authors.lastname: Tohidi
authors.affiliation: Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, P.O. Box 19395-4763, Tehran, Islamic Republic of Iran. Electronic address: fereidoun.azizi@gmail.com.
authors.forename: F
authors.initials: F
authors.lastname: Azizi
mesh_terms: D000328:Adult; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007333:Insulin Resistance / Q000502:physiology*; D007492:Iran / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D013961:Thyroid Gland / Q000276:immunology*; D013963:Thyroid Hormones / Q000097:blood / Q000502:physiology*; D055815:Young Adult
chemical_list: D013963:Thyroid Hormones
keywords: Free thyroxine; Insulin resistance; TSH; Thyroid