title: Moderate weight loss is sufficient to affect thyroid hormone homeostasis and inhibit its peripheral conversion.
abstract: BACKGROUND
  Thyroid hormones are important determinants of energy expenditure, and in rodents, adipose tissue affects thyroid hormone homeostasis via leptin signaling. The relationship between thyroid hormones and nutritional status in humans has been assessed primarily in drastic dietary or bariatric surgery interventions, while limited information is available on serial assessment of this axis during moderate, prolonged dietary restriction.
  
  
  METHODS
  To evaluate the effects of moderate dietary restriction on thyroid hormone homeostasis, 47 subjects with a body mass index (BMI) of 25-45 kg/m(2) were enrolled in a longitudinal intervention study; 30 nonoverweight volunteers were also enrolled as controls. Overweight and obese subjects underwent a 12-month individualized dietary intervention aimed at achieving a 5-10% weight loss.
  
  
  RESULTS
  The intervention resulted in a 6.3±0.9 kg (6.5±1.0%) weight loss. At baseline, thyrotropin (TSH) and T3 concentrations correlated significantly with fat mass (R=0.257, p=0.024 and R=0.318, p=0.005, respectively). After weight loss, T3 decreased significantly (from 112.7±3.1 to 101.8±2.6 ng/dL, p<0.001) in the absence of significant changes in TSH or free T4 (fT4). The decrease in serum T3 correlated with the decrease in weight (R=0.294, p<0.001). The T3:fT4 ratio decreased significantly (p=0.02) in individuals who lost >5% body weight.
  
  
  CONCLUSIONS
  T3 concentration closely correlates with individual nutritional status, and moderate weight loss results in a decrease in T3 with minimal changes in other thyroid hormone homeostasis parameters. The data suggest that a decrease in peripheral conversion of the prohormone T4 into its hormonally active metabolite T3 is at least in part responsible for the observed changes in thyroid hormone homeostasis.
authors.affiliation: 1 Diabetes, Endocrinology, and Obesity Branch, National Institutes of Health , Bethesda, Maryland.
authors.forename: Ritesh V
authors.initials: RV
authors.lastname: Agnihothri
authors.forename: Amber B
authors.initials: AB
authors.lastname: Courville
authors.forename: Joyce D
authors.initials: JD
authors.lastname: Linderman
authors.forename: Sheila
authors.initials: S
authors.lastname: Smith
authors.forename: Robert
authors.initials: R
authors.lastname: Brychta
authors.forename: Alan
authors.initials: A
authors.lastname: Remaley
authors.forename: Kong Y
authors.initials: KY
authors.lastname: Chen
authors.forename: Louis
authors.initials: L
authors.lastname: Simchowitz
authors.forename: Francesco S
authors.initials: FS
authors.lastname: Celi
mesh_terms: D000273:Adipose Tissue / Q000473:pathology; D000328:Adult; D015992:Body Mass Index; D004734:Energy Metabolism; D005260:Female; D006706:Homeostasis; D006801:Humans; D008297:Male; D009765:Obesity / Q000097:blood; D013961:Thyroid Gland / Q000502:physiology; D013963:Thyroid Hormones / Q000097:blood*; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood*; D015431:Weight Loss
chemical_list: D013963:Thyroid Hormones; D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine
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