A randomized placebo-controlled clinical trial of the effectiveness of thyroxine and triiodothyronine and short-term exposure to bright light in prevention of decrements in cognitive performance and mood during prolonged Antarctic residence.
OBJECTIVE
We examined the effects of a combined levothyroxine/liothyronine supplement and exposure to bright (10,000 lux) light in euthyroid men and women who spent the austral summer (n = 43) and/or winter (n = 42) in Antarctica.


METHODS
Subjects were randomized to receive 64 nmol of levothyroxine and 16 nmol of liothyronine supplement or a placebo capsule for 93.2 +/- 3.0 days in summer and/or 149.5 +/- 2.2 days in winter. Subjects were further randomized to receive 10,000 lux bright white light or 50 lux dim red light for 14 days at the end of summer and/or winter. Cognitive performance and mood were assessed using the Automatic Neuropsychological Assessment Metric - Isolated and Confined Environments.


RESULTS
In winter, bright light exposure was associated with a significantly greater reduction in TSH and anger (P < 0.05), a significantly greater increase in fT(3) (P < 0.05), and a significantly smaller increase in depressive symptoms (P < 0.001), when compared with dim light. The T4/T3 supplement also led to a significantly greater reduction in TSH (P < 0.05), but a greater reduction in cognitive task efficiency (P < 0.05) as well, when compared with placebo.


CONCLUSIONS
Administration of bright light leads to a significant reduction in serum TSH and prevents increases in anger and depressive symptoms in winter. However, these associations were not observed in summer, suggesting a seasonal influence of photoperiod over temperature upon this intervention in the polar environment.
Palinkas
Lawrence A
LA
School of Social Work and Departments of Anthropology and Preventive Medicine, University of Southern California, Los Angeles, CA 90089-0411, USA. palinkas@usc.edu
Reedy
Kathleen R
KR
Shepanek
Marc
M
Reeves
Dennis
D
Samuel Case
H
H
Van Do
Nhan
N
Lester Reed
H
H
D000328:Adult; D000339:Affect / Q000187:drug effects*; D000786:Anger / Q000187:drug effects; D000864:Antarctic Regions; D003071:Cognition / Q000187:drug effects*; D003863:Depression / Q000628:therapy*; D005260:Female; D006801:Humans; D008029:Lighting; D008297:Male; D017440:Photoperiod; D010789:Phototherapy; D012621:Seasons; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000494:pharmacology*; D014284:Triiodothyronine / Q000494:pharmacology*
D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine