title: Thyroid hyperactivity with high thyroglobulin in serum despite sufficient iodine intake in chronic cold adaptation in an Arctic Inuit hunter population.
abstract: OBJECTIVE
  Adult man hosts brown adipose tissue with the capacity to consume energy and dissipate heat. This is essential for non-shivering thermogenesis and its activation depends on sympathetic activity and thyroid hormones. This led us to evaluate the impact of chronic cold exposure on thyroid activity and thyroid hormones in serum in Arctic residents.
  
  
  METHODS
  Comparative, population-based study (n = 535) performed in Greenland.
  
  
  METHODS
  Hunters were compared with other men, and Inuit in remote settlements in East Greenland with no modern housing facilities were compared with the residents of the capital city in West Greenland and residents of a major town in East Greenland in a cross-sectional study. We used interview-based questionnaires, measured TSH, free thyroxine, free triiodothyronine (fT(3)), thyroglobulin (TG) antibody and TG (a measure of thyroid activity) in serum, and iodine and creatinine in spot urine samples.
  
  
  RESULTS
  Serum TG was the highest among hunters (P = 0.009) and settlement dwellers (P = 0.001), who were most markedly exposed to cold, even though they had the highest urinary iodine excretion (hunters, P < 0.001; settlement dwellers, P < 0.001). Hunters and settlement dwellers also had the lowest fT(3) (hunters, P < 0.001; settlement dwellers, P < 0.001) after adjusting for gender, age, smoking habits, alcohol intake and iodine excretion in multivariate linear regression models. TSH was not influenced by measures of cold exposure (hunter, P = 0.36; residence, P = 0.91).
  
  
  CONCLUSIONS
  Cold exposure influenced thyroid hormones and TG in serum in Arctic populations consistent with consumption of thyroid hormone and higher thyroid hormone turnover. Findings emphasise that changes in thyroid activity are essential in cold adaptation in Arctic residents.
authors.affiliation: Arctic Health Research Centre, Aalborg University Hospital, Hobrovej 42D, 9000 Aalborg, Denmark. stiga@dadlnet.dk
authors.forename: Stig
authors.initials: S
authors.lastname: Andersen
authors.forename: Kent
authors.initials: K
authors.lastname: Kleinschmidt
authors.forename: Bodil
authors.initials: B
authors.lastname: Hvingel
authors.forename: Peter
authors.initials: P
authors.lastname: Laurberg
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000368:Aged; D003080:Cold Temperature; D003430:Cross-Sectional Studies; D005260:Female; D006116:Greenland / Q000208:ethnology; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood* / Q000208:ethnology / Q000652:urine; D004930:Inuit / Q000208:ethnology; D007455:Iodine / Q000008:administration & dosage* / Q000652:urine; D008297:Male; D008875:Middle Aged; D011159:Population Surveillance / Q000379:methods; D013954:Thyroglobulin / Q000096:biosynthesis / Q000097:blood*
chemical_list: D013954:Thyroglobulin; D007455:Iodine