Impairment in Cognitive and Exercise Performance during Prolonged Antarctic Residence: Effect of Thyroxine Supplementation in the Polar Triiodothyronine Syndrome1

• Published in: The journal of clinical endocrinology and metabolism 2001-01, Vol.86 (1), p.110-116
• Main Authors: Reed, H. Lester, Reedy, Kathleen R., Palinkas, Lawrence A., Van Do, Nhan, Finney, Nancy S., Case, H. Samuel, LeMar, Homer J., Wright, James, Thomas, John
• Format: Article
• Language: English
• ISSN: 0021-972X; 1945-7197
• DOI: 10.1210/jcem.86.1.7092

Humans who work in Antarctica display deficits in cognition, disturbances in mood, increased energy requirements, a decline of thyroid hormone products, and an increase of serum TSH. We compared measurements in 12 subjects, before deployment (baseline), with 11 monthly studies during Antarctic residence (AR). After 4 months of AR (period 1), half of the subjects (T4 group) received l-thyroxine [64 nmol·day−1 (0.05 mg·day−1)]; and the other half, a placebo (placebo group) for the next 7 months of AR (period 2). During period 1, there was a 12.3 ± 5.1% (P< 0.03) decline on the matching-to-sample (M-t-S) cognitive task and an increase in depressive symptoms, compared with baseline. During the intervention in period 2, M-t-S scores for the T4-treated group returned to baseline values; whereas the placebo group, in contrast, showed a reduced M-t-S score (11.2 ± 1.3%; P < 0.0003) and serum free T4 (5.9 ± 2.4%; P < 0.02), compared with baseline. The change in M-t-S score was correlated with the change in free T4 (P < 0.0003) during both periods, and increases in serum TSH preceded worsening scores in depression, tension, anger, lack of vigor, and total mood disturbance (P < 0.001) during period 2. Additionally, the submaximal work rate for a fixed O2 use decreased 22.5± 4.9% in period 1 and remained below baseline in period 2 (25.2± 2.3%; P < 0.005) for both groups. After 4 months of AR, the l-thyroxine supplement was associated with improved cognition, which seems related to circulating T4. Submaximal exercise performance decrements, observed during AR, were not changed with this l-thyroxine dose.