title: Seasonal levels of melatonin, thyroid hormones, mood, and cognition near the Arctic Circle.
abstract: BACKGROUND
  The associations between melatonin and thyroid hormones and changes in mood and cognitive performance caused by exposure to cold and darkness were examined in 12 circumpolar residents during winter and summer.
  
  
  METHODS
  Each participant was exposed to three different experimental conditions in random order: 1) 22 degrees C and bright light; 2) 10 degrees C and bright light; and 3) 10 degrees C and dim light. The duration of each exposure was 24 h.
  
  
  RESULTS
  Increased serum melatonin and thyrotropin were associated with decreased rectal temperature (r = -0.446 - -0.580) and increased mean skin temperature (r = 0.204-0.519). Higher serum melatonin was associated with increased vigor (r = 0.330) and decreased accuracy on simple cognitive tasks (r = -0.332 - -0.430). Increased serum free triiodothyronine (fT3) was associated with decreased negative mood scores (r = -0.365 - -0.483), decreased response time (RT) on the simple reaction time (SRT) task (r = -0.606), and decreased accuracy on the addition/subtraction task (r = -0.372). Higher serum free thyroxine was associated with decreased fatigue and anger (r = -0.409 - -0.522). Increased serum thyrotropin was associated with decreased accuracy and RT on the SRT task and decreased RT on the grammatical reasoning task (r = -0.315 - -0.415).
  
  
  CONCLUSIONS
  Associations between serum melatonin and thyroid hormones with mood were consistent with the psychological changes associated with the polar triiodothyronine syndrome. Also, serum melatonin and thyrotropin were associated with impaired and fT3 with improved cognitive performance, supporting the decrements in cognitive performance associated with the polar triiodothyronine syndrome.
authors.affiliation: Department of Biomedicine/Physiology, University of Oulu, Oulu, Finland. tiina.paakkonen@oulu.fi
authors.forename: Tiina
authors.initials: T
authors.lastname: Pääkkönen
authors.forename: Juhani
authors.initials: J
authors.lastname: Leppäluoto
authors.forename: Tiina M
authors.initials: TM
authors.lastname: Mäkinen
authors.forename: Hannu
authors.initials: H
authors.lastname: Rintamäki
authors.forename: Aimo
authors.initials: A
authors.lastname: Ruokonen
authors.forename: Juhani
authors.initials: J
authors.lastname: Hassi
authors.forename: Lawrence A
authors.initials: LA
authors.lastname: Palinkas
mesh_terms: D000328:Adult; D000339:Affect; D001110:Arctic Regions; D003071:Cognition; D003081:Cold Climate; D005387:Finland; D006801:Humans; D008297:Male; D008550:Melatonin / Q000097:blood*; D017440:Photoperiod; D011930:Reaction Time; D016574:Seasonal Affective Disorder / Q000097:blood; D012621:Seasons; D013963:Thyroid Hormones / Q000097:blood*
chemical_list: D013963:Thyroid Hormones; D008550:Melatonin