title: Improvements in insulin sensitivity are blunted by subclinical hypothyroidism.
abstract: OBJECTIVE
  Exercise- and weight loss-induced improvements in insulin resistance (IR) are variable; some individuals experience robust enhancements in insulin sensitivity, whereas others do not. Thyroid hormone status is related to IR, but it is not clear whether subclinical hypothyroidism may help to explain the variability in improvements in IR with diet and exercise. The purpose of this study was to examine whether thyroid hormone status is related to the improvement in insulin sensitivity and physical fitness after weight loss and exercise training.
  
  
  METHODS
  By retrospective nested case-control analysis, eight subclinical hypothyroid (sHT) subjects and eight matched euthyroid controls underwent a euglycemic hyperinsulinemic clamp and peak oxygen uptake test, before and after a 16-wk program of moderate aerobic exercise combined with diet-induced weight loss. All subjects were middle-aged (57.3 +/- 3.3 yr), were overweight to obese (body mass index = 33.1 +/- 0.8 kg m(-2)), and had impaired glucose tolerance.
  
  
  RESULTS
  The improvement in insulin sensitivity was significantly lower (P < 0.05) in the sHT group than in the euthyroid group. Both groups performed similar amounts of regular exercise and lost a significant amount of body weight during the intervention. VO(2peak) tended to improve in the euthyroid group but not in the sHT group.
  
  
  CONCLUSIONS
  Subclinical hypothyroidism may interfere with beneficial adaptations on muscle metabolism and physical fitness that typically occur with weight loss and increased physical activity. These results may have significant clinical implications because of the high prevalence of both hypothyroidism and insulin resistance in the aging population.
authors.affiliation: Department of Health and Physical Activity, School of Education, University of Pittsburgh, PA 15213, USA.
authors.forename: Francesca
authors.initials: F
authors.lastname: Amati
authors.forename: John J
authors.initials: JJ
authors.lastname: Dubé
authors.forename: Maja
authors.initials: M
authors.lastname: Stefanovic-Racic
authors.forename: Frederico G
authors.initials: FG
authors.lastname: Toledo
authors.forename: Bret H
authors.initials: BH
authors.lastname: Goodpaster
mesh_terms: D016022:Case-Control Studies; D015444:Exercise; D005081:Exercise Therapy; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000150:complications* / Q000503:physiopathology; D007333:Insulin Resistance / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009043:Motor Activity; D009765:Obesity / Q000150:complications / Q000503:physiopathology* / Q000628:therapy; D016896:Treatment Outcome; D015431:Weight Loss