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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.

Author(s): Palinkas LA, Reedy KR, Shepanek M, Reeves D, Samuel Case H, Van Do N, Lester Reed H

Affiliation(s): School of Social Work and Departments of Anthropology and Preventive Medicine, University of Southern California, Los Angeles, CA 90089.

Publication date & source: 2009-07-24, Clin Endocrinol (Oxf)., [Epub ahead of print]

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 to 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 to placebo. Conclusion: 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.

Page last updated: 2009-10-20

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