title: Hyperthyroidism increases brown fat metabolism in humans.
abstract: BACKGROUND
  Thyroid hormones are important regulators of brown adipose tissue (BAT) development and function. In rodents, BAT metabolism is up-regulated by thyroid hormones.
  
  
  OBJECTIVE
  The purpose of this article was to investigate the impact of hyperthyroidism on BAT metabolism in humans.
  
  
  METHODS
  This was a follow-up study using positron emission tomography imaging.
  
  
  METHODS
  Glucose uptake (GU) and perfusion of BAT, white adipose tissue, skeletal muscle, and thyroid gland were measured using [18F]2-fluoro-2-deoxy-D-glucose and [15O]H2O and positron emission tomography in 10 patients with overt hyperthyroidism and in 8 healthy participants. Five of the hyperthyroid patients were restudied after restoration of euthyroidism. Supraclavicular BAT was quantified with magnetic resonance imaging or computed tomography and energy expenditure (EE) with indirect calorimetry.
  
  
  RESULTS
  Compared with healthy participants, hyperthyroid participants had 3-fold higher BAT GU (2.7±2.3 vs 0.9±0.1 μmol/100 g/min, P=.0013), 90% higher skeletal muscle GU (P<.005), 45% higher EE (P<.005), and a 70% higher lipid oxidation rate (P=.001). These changes were reversible after restoration of euthyroidism. During hyperthyroidism, serum free T4 and free T3 were strongly associated with EE and lipid oxidation rates (P<.001). TSH correlated inversely with BAT and skeletal muscle glucose metabolism (P<.001). Hyperthyroidism had no effect on BAT perfusion, whereas it stimulated skeletal muscle perfusion (P=.04). Thyroid gland GU did not differ between hyperthyroid and euthyroid study subjects.
  
  
  CONCLUSIONS
  Hyperthyroidism increases GU in BAT independently of BAT perfusion. Hyperthyroid patients are characterized by increased skeletal muscle metabolism and lipid oxidation rates.
authors.affiliation: Turku PET Centre (M.L., J.O., M.S., J.C.H., A.K., K.A.V., P.N.), University of Turku, 20520 Turku, Finland; Division of Endocrinology (C.S.-J.), Department of Medicine, University of Helsinki and Helsinki University Hospital, 00014 Helsinki, Finland; Department of Endocrinology (M.S., P.J.) and Department of Nuclear Medicine (T.N.), Turku University Hospital, 20520 Turku, Finland; Department of Investigative Radiology (H.I.), National Cerebral and Cardiovascular Center Research Institute, Osaka 565-8565, Japan; Department of Medical Physics (N.K.), Faculty of Medicine, Kagawa University, Kagawa 760-0016, Japan; and Medical Genetics (S.E.), Department of Medical Biochemistry, University of Gothenburg, 411 37 Gothenburg, Sweden.
authors.forename: Minna
authors.initials: M
authors.lastname: Lahesmaa
authors.forename: Janne
authors.initials: J
authors.lastname: Orava
authors.forename: Camilla
authors.initials: C
authors.lastname: Schalin-Jäntti
authors.forename: Minna
authors.initials: M
authors.lastname: Soinio
authors.forename: Jarna C
authors.initials: JC
authors.lastname: Hannukainen
authors.forename: Tommi
authors.initials: T
authors.lastname: Noponen
authors.forename: Anna
authors.initials: A
authors.lastname: Kirjavainen
authors.forename: Hidehiro
authors.initials: H
authors.lastname: Iida
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Kudomi
authors.forename: Sven
authors.initials: S
authors.lastname: Enerbäck
authors.forename: Kirsi A
authors.initials: KA
authors.lastname: Virtanen
authors.forename: Pirjo
authors.initials: P
authors.lastname: Nuutila
mesh_terms: D002001:Adipose Tissue, Brown / Q000000981:diagnostic imaging / Q000378:metabolism*; D052436:Adipose Tissue, White / Q000000981:diagnostic imaging / Q000378:metabolism; D000328:Adult; D016022:Case-Control Studies; D005260:Female; D019788:Fluorodeoxyglucose F18; D005500:Follow-Up Studies; D006801:Humans; D006980:Hyperthyroidism / Q000000981:diagnostic imaging / Q000378:metabolism*; D050356:Lipid Metabolism / Q000502:physiology; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging / Q000378:metabolism; D010104:Oxygen Radioisotopes; D049268:Positron-Emission Tomography; D015854:Up-Regulation; D014867:Water
chemical_list: D010104:Oxygen Radioisotopes; D014867:Water; D019788:Fluorodeoxyglucose F18