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. 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.

Psychoneuroendocrine effects of combined thyroxine and triiodothyronine versus tyrosine during prolonged Antarctic residence.

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) 50 microg of levothyroxine and 12.5 microg 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.

Resting and exercise energy use in Antarctica: effect of 50% restriction in temperate climate energy requirements.

OBJECTIVE: To determine the impact of energy restriction (ER) upon the previously reported increased resting and exercise-related oxygen utilization, reduced body temperature, increased serum TSH, and reduced serum free T3 concentrations found during Antarctic residence (AR). DESIGN: Prospective, intervention with both paired controls and a similar reference control group (RG). PATIENTS AND MEASUREMENTS: Seven subjects were assessed before and after a 50% ER period of 60 h. This ER was carried out within 30 days of arriving in Antarctica in October (OCT) and again after 10 months AR in August (AUG). During the periods of ER, mean energy consumption was 5662 +/- 1344 kJ/day in OCT and 5529 +/- 967 kJ/day in AUG. Resting metabolic rate (RMR), a calculated resting metabolic rate (RMR(reg)) using a submaximal work regression, serum TSH, FT3 and tympanic temperature (Tty) were measured. These values were compared with a similar RG of 12 subjects reported previously who were studied in California, USA before and then again during AR. RESULTS: Weight declined by 1.1 +/- 0.1 kg/day (OCT) and 0.92 +/- 0.2 kg/day (AUG) with ER, resulting in a reduction of body weight by 3.1 +/- 0.4% in OCT (P = 0.0001) and 2.5 +/- 0.4% in AUG (P = 0.0015) during AR. The RMR before ER did not change with AR and it was not significantly different from the RG studied in California. With ER the RMR tended to decline in both OCT (132 +/- 5 to 122 +/- 4 mlO2/min/m2) and AUG (134 +/- 5 to 126 +/- 5 mlO2/min/m2), but these were not significant. By contrast, RMR(reg) obtained before ER was increased with AR by 22.5 +/- 7.8% (P = 0.01) in OCT and by 28.1 +/- 7.0% (P = 0.0008) in AUG over the RG values obtained in California. RMR(reg) did not decrease with ER in either OCT or AUG. The total energy expenditure derived from these measures of weight loss suggests that 24-h energy requirements are 74.4%[95% confidence interval (CI) 2.6-146.3; P < 0.05] more than those expected in temperate climates. Tty declined by 0.6 +/- 0.2 degrees C (P < 0.01) with AR compared with the RG measured in California, but was not affected by either period of ER. ER had no effect on FT3 but tended to decrease serum TSH in AUG (P = 0.06). CONCLUSIONS: Exercise-related energy requirements are increased with AR. Moderate ER may reduce resting but not exercise-related energy expenditure and it is associated with a weight loss exceeding expectations for 50% restriction of temperate climate energy predictions.