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

• Published in: Clinical Endocrinology
• Main Authors: Palinkas, Lawrence A., Reedy, Kathleen R., Shepanek, Marc, Reeves, Dennis, Samuel Case, H., Van Do, Nhan, Lester Reed, H.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2010
• Subjects: Antarctic; Austral; Antarc*; Antarctica
• Online Access: http://dx.doi.org/10.1111/j.1365-2265.2009.03669.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1365-2265.2009.03669.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2265.2009.03669.x

Summary 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. 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.