title: The impact of the metabolic phenotype on thyroid function in obesity.
abstract: BACKGROUND
  Obesity is known to promote mild hyperthyrotropinaemia by unknown metabolic mechanisms. This investigation aimed to explore the association between thyroid function and metabolic phenotype in euthyroid obese individuals. Retrospective, cross-sectional study. Tertiary care center.
  
  
  METHODS
  952 euthyroid obese individuals referred to our Institution for obesity. Serum levels of TSH, FT4, glucose, insulin and HbA1c levels, lipid profile, liver function and proinflammatory indices were measured. Resting energy expenditure was assessed by indirect calorimetry and body composition by bioimpedance analysis.
  
  
  RESULTS
  On admission, 306 patients had previously diagnosed diabetes mellitus on treatment with metformin, while 113 patients were diagnosed with incident diabetes mellitus. Serum TSH levels were similar between metformin-treated diabetic subjects and metformin-untreated subjects, while FT4 was slightly but significantly higher in the former. Analysis stratified by TSH categories found no effect of metformin-treated diabetes mellitus on TSH levels. Interestingly, obese patients with incident diabetes showed lower TSH levels than normoglycaemic ones. In correlation studies on the whole dataset, an association related TSH to BMI and total cholesterol levels, which was lost upon adjustment for individual confounders. FT4 levels were found to be inversely related to BMI, insulin resistance and triglycerides, while being directly associated with HDL-cholesterol levels. These correlations remained unaltered after controlling for individual confounders. In multivariate linear regression analysis, TSH was associated with FT4, total cholesterol and BMI values. Significant predictors of FT4 were constituted by previously diagnosed diabetes mellitus, BMI, TSH and age.
  
  
  CONCLUSIONS
  In euthyroid obese subjects, FT4 seems more closely related than TSH levels to parameters of cardiometabolic risk. TSH levels did not differ between metformin-treated and untreated subjects, while they were lower in patients with incident diabetes mellitus compared to normoglycaemic ones.
authors: Division of General Medicine, I.R.C.C.S. Istituto Auxologico Italiano, Ospedale S. Giuseppe, Casella Postale 1, 28921 Verbania, Italy ; Endocrinology, Università del Piemonte Orientale, 28100 Novara, Italy.
authors: Paolo
authors: P
authors: Marzullo
authors: Division of General Medicine, I.R.C.C.S. Istituto Auxologico Italiano, Ospedale S. Giuseppe, Casella Postale 1, 28921 Verbania, Italy ; Endocrinology, Università del Piemonte Orientale, 28100 Novara, Italy.
authors: Chiara
authors: C
authors: Mele
authors: Laboratory of Metabolic Research, I.R.C.C.S. Istituto Auxologico Italiano, Ospedale S. Giuseppe, 28921 Verbania, Italy.
authors: Stefania
authors: S
authors: Mai
authors: Division of General Medicine, I.R.C.C.S. Istituto Auxologico Italiano, Ospedale S. Giuseppe, Casella Postale 1, 28921 Verbania, Italy.
authors: Gabriele
authors: G
authors: Guzzaloni
authors: Division of Biostatistics, Epidemiology and Public Health, Department of Statistics and Quantitative Methods, University of Milano-Bicocca, 20126 Milan, Italy.
authors: Davide
authors: D
authors: Soranna
authors: Division of General Medicine, I.R.C.C.S. Istituto Auxologico Italiano, Ospedale S. Giuseppe, Casella Postale 1, 28921 Verbania, Italy.
authors: Maria Antonella
authors: MA
authors: Tagliaferri
authors: Division of General Medicine, I.R.C.C.S. Istituto Auxologico Italiano, Ospedale S. Giuseppe, Casella Postale 1, 28921 Verbania, Italy.
authors: Maria Elisa
authors: ME
authors: Berselli
authors: Endocrinology, Università del Piemonte Orientale, 28100 Novara, Italy.
authors: Flavia
authors: F
authors: Prodam
authors: Division of Obstetrics and Gynaecology, Department of Translational Medicine, Università del Piemonte Orientale, 28100 Novara, Italy.
authors: Daniela
authors: D
authors: Surico
authors: Endocrinology, Università del Piemonte Orientale, 28100 Novara, Italy.
authors: Gianluca
authors: G
authors: Aimaretti
authors: Division of General Medicine, I.R.C.C.S. Istituto Auxologico Italiano, Ospedale S. Giuseppe, Casella Postale 1, 28921 Verbania, Italy ; Department of Clinical Sciences and Community Health, University of Milan, 20122 Milan, Italy.
authors: Massimo
authors: M
authors: Scacchi
keywords: Diabetes mellitus; Metformin; Obesity; Thyroid