title: High-normal TSH values in obesity: is it insulin resistance or adipose tissue's guilt?
abstract: OBJECTIVE
  Clinical evidences reported subclinical alterations of thyroid function in obesity, although the relationship between thyroid status and obesity remains unclear. We cross-sectionally investigated the influence of metabolic features on hypothalamic-pituitary-thyroid axis in obesity.
  
  
  METHODS
  We enrolled 60 euthyroid subjects with no history of type 2 diabetes mellitus and assessed the relationship of thyroid function with insulin resistance, measured using euglycemic clamp, and abdominal fat volume, quantified by computed tomography scan (CT scan). Thyroid stimulating hormone (TSH) correlated with BMI (r = 0.46; P = 0.02), both visceral (r = 0.58; P = 0.02) and subcutaneous adipose tissue volumes (r = 0.43; P = 0.03) and insulin resistance (inverse relationship with insulin sensitivity-glucose uptake: r = -0.40; P = 0.04).
  
  
  RESULTS
  After performing multivariate regression, visceral adipose tissue volume was found to be the most powerful predictor of TSH (β = 3.05; P = 0.01), whereas glucose uptake, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, subcutaneous adipose tissue volume, and triglycerides were not. To further confirm the hypothesis that high-normal TSH values could be dependent on adipose tissue, and not on insulin resistance, we restricted our analyses to moderately obese subjects' BMI ranging 30-35 kg/m(2). This subgroup was then divided as insulin resistant and insulin sensitive according to the glucose uptake (≤ or >5 mg · kg(-1) · min(-1), respectively). We did not find any statistical difference in TSH (insulin resistant: 1.62 ± 0.65 µU/ml vs. insulin sensitive: 1.46 ± 0.48; P = not significant) and BMI (insulin resistant: 32.2 ± 1.6 kg/m(2) vs. insulin sensitive: 32.4 ± 1.4; P = not significant), thus confirming absence of correlation between thyroid function and insulin sensitivity per se.
  
  
  CONCLUSIONS
  Our study suggests that the increase in visceral adipose tissue is the best predictor of TSH concentration in obesity, independently from the eventual concurrent presence of insulin resistance.
authors.affiliation: Department of Endocrinology and Metabolic Diseases, Università Cattolica, Rome, Italy. giovanna.muscogiuri@gmail.com
authors.forename: Giovanna
authors.initials: G
authors.lastname: Muscogiuri
authors.forename: Gian P
authors.initials: GP
authors.lastname: Sorice
authors.forename: Teresa
authors.initials: T
authors.lastname: Mezza
authors.forename: Annamaria
authors.initials: A
authors.lastname: Prioletta
authors.forename: Anna P
authors.initials: AP
authors.lastname: Lassandro
authors.forename: Tommaso
authors.initials: T
authors.lastname: Pirronti
authors.forename: Silvia
authors.initials: S
authors.lastname: Della Casa
authors.forename: Alfredo
authors.initials: A
authors.lastname: Pontecorvi
authors.forename: Andrea
authors.initials: A
authors.lastname: Giaccari
mesh_terms: D000328:Adult; D000368:Aged; D001823:Body Composition; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D005260:Female; D005947:Glucose / Q000378:metabolism; D015309:Glucose Clamp Technique; D006801:Humans; D007030:Hypothalamo-Hypophyseal System / Q000502:physiology; D007333:Insulin Resistance; D050152:Intra-Abdominal Fat / Q000378:metabolism*; D008055:Lipids / Q000097:blood; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009765:Obesity / Q000097:blood / Q000150:complications / Q000378:metabolism*; D013972:Thyrotropin / Q000097:blood*
chemical_list: D008055:Lipids; D013972:Thyrotropin; D005947:Glucose