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

摘要

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.