Psychoneuroendocrine effects of combined thyroxine and triiodothyronine versus tyrosine during prolonged Antarctic residence
Palinkas LA, Reedy KR, Smith M, Anghel M, Steel GD, Reeves D, Shurtleff D, Case HS, Van Do N, Reed HL

 

ABSTRACT [full text] [back to issue 66(5)]

Objectives. 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.

Study Design. 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) 50ug of levothyroxine and 12.5ug 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.
(Int J Circumpolar Health 2007; 66(5):401-417)

Keywords: mood, cognition, cold, thyroid hormones, clinical trial, tyrosine