title: Psychoneuroendocrine effects of combined thyroxine and triiodothyronine versus tyrosine during prolonged Antarctic residence.
abstract: OBJECTIVE
  We previously reported that cognitive function improves with thyroxine and that there is a circannual pattern to mood and human TSH during Antarctic residence. To extend these findings, we examined the effects of tyrosine and a combined levothyroxine/liothyronine supplement in euthyroid men and women who spent the austral summer (n = 43) and/or winter (n = 42) in Antarctica.
  
  
  METHODS
  Randomized, placebo-controlled, clinical trial.
  
  
  METHODS
  Subjects were randomized to receive the following each day for 91.6 +/- 3.2 days in summer and/or 138.0 +/- 3.2 days in winter: (1) 12g tyrosine mixed in 113g applesauce; (2) 50 microg of levothyroxine and 12.5 microg of liothyronine (T4-T3 Supplement); or (3) placebo. Cognitive performance and mood were assessed using the Automatic Neuropsychological Assessment Metric - Isolated and Confined Environments.
  
  
  RESULTS
  With placebo in summer, mood did not change while TSH decreased by 28%; in winter, there was a 136% degradation in mood (p < 0.01) and TSH increased by 18%. With combined T4-T3 supplement, there was a 51% degradation in mood in summer compared with placebo (p < 0.05) and TSH decreased by 57%; in winter there was a 135% degradation in mood while TSH was reduced by 26% (p < 0.05). Tyrosine use in summer was associated with no change in mood and a 30% decline in TSH, while in winter there was a 47% improvement in mood and TSH decreased by 28% along with a 6% increase in fT3 (p < 0.05).
  
  
  CONCLUSIONS
  Administration of tyrosine leads to a significant reduction in serum TSH and improvement in mood in winter compared with placebo, while the combined T4-T3 supplement leads to a worsening of mood in summer and no improvement in winter. There appears to be a seasonal influence on the psychological response to interventions and the relationship to changes in TSH reductions.
authors.affiliation: School of Social Work and Department of Anthropology, University of Southern California, Los Angeles 90089-0411, USA. palinkas@usc.edu
authors.forename: Lawrence A
authors.initials: LA
authors.lastname: Palinkas
authors.forename: Kathleen R
authors.initials: KR
authors.lastname: Reedy
authors.forename: Mark
authors.initials: M
authors.lastname: Smith
authors.forename: Mihai
authors.initials: M
authors.lastname: Anghel
authors.forename: Gary D
authors.initials: GD
authors.lastname: Steel
authors.forename: Dennis
authors.initials: D
authors.lastname: Reeves
authors.forename: David
authors.initials: D
authors.lastname: Shurtleff
authors.forename: H Samuel
authors.initials: HS
authors.lastname: Case
authors.forename: Nhan
authors.initials: N
authors.lastname: Van Do
authors.forename: H Lester
authors.initials: HL
authors.lastname: Reed
mesh_terms: D000328:Adult; D000339:Affect / Q000187:drug effects*; D000864:Antarctic Regions; D003071:Cognition / Q000187:drug effects*; D004338:Drug Combinations; D005260:Female; D006801:Humans; D008297:Male; D012621:Seasons; D013963:Thyroid Hormones / Q000097:blood; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000627:therapeutic use*; D014284:Triiodothyronine / Q000627:therapeutic use*; D014443:Tyrosine / Q000627:therapeutic use*
chemical_list: D004338:Drug Combinations; D013963:Thyroid Hormones; D014284:Triiodothyronine; D014443:Tyrosine; C018539:thyroxine, triiodothyronine drug combination; D013972:Thyrotropin; D013974:Thyroxine