title: Serum free thyroxine concentration is associated with metabolic syndrome in euthyroid subjects.
abstract: BACKGROUND
  The association between thyroid hormones within the euthyroid range and metabolic syndrome is not clear.
  
  
  OBJECTIVE
  This study evaluated the relationship between thyroid hormones and metabolic syndrome and its components in euthyroid subjects.
  
  
  METHODS
  This is a cross-sectional population based study conducted within the framework of the cohort of the Tehran Thyroid Study.
  
  
  METHODS
  Out of 5786 subjects aged ≥ 20 years, 3755 euthyroid subjects without a history of thyroid disorders, diabetes, or use of steroids or lipid-lowering agents were investigated.
  
  
  METHODS
  Body weight, waist circumference (WC), and blood pressure (BP) were measured. Serum concentrations of lipids and lipoproteins, fasting blood glucose (FBG), insulin, free T4 (FT4), and thyrotropin (TSH) were assayed. Metabolic syndrome was determined by definition of the Joint Interim Statement adjusted for the Iranian population.
  
  
  RESULTS
  After adjustment for age, sex, and smoking, serum FT4 was significantly associated with high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), triglycerides (TGs), WC, systolic BP, and diastolic BP; the associations that remained significant after further adjustment for body mass index (BMI) and the homeostasis model assessment index for insulin resistance (HOMA-IR) except for HDL-C. Serum TSH was associated only with TGs after adjustments for age, sex, smoking, and BMI, an association that disappeared after further adjustment for HOMA-IR. Serum FT4 was negatively associated (β=-0.02, 95% confidence interval [CI: -0.03, -0.01]) and TSH was positively associated (β = 0.03 [CI: 0.01, 0.04) with insulin resistance. The prevalence of metabolic syndrome decreased from 30.1% in the lowest FT4 tertile to 22.4% in the highest FT4 tertile (p<0.001). The prevalence of other metabolic syndrome components decreased significantly from higher to lower FT4 tertiles. Higher FT4 values were associated with lower odds of metabolic syndrome (OR = 0.96 [95% CI: 0.92, 0.99]; p=0.01).
  
  
  CONCLUSIONS
  In euthyroid subjects, FT4, rather than TSH, is associated with risk of metabolic syndrome and its components.
authors: 1 Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences , Tehran, I. R. Iran .
authors: Ladan
authors: L
authors: Mehran
authors: Atieh
authors: A
authors: Amouzegar
authors: Maryam
authors: M
authors: Tohidi
authors: Maryam
authors: M
authors: Moayedi
authors: Fereidoun
authors: F
authors: Azizi
mesh_terms: D000328:Adult; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance; D007492:Iran; D008055:Lipids / Q000097:blood*; D008297:Male; D024821:Metabolic Syndrome / Q000097:blood*; D008875:Middle Aged; D013960:Thyroid Function Tests; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood; D055105:Waist Circumference; D055815:Young Adult
chemical_list: D007328:Insulin; D008055:Lipids; D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine