Thyroid function during a prolonged stay in Antarctica

Abstract

Adaptation of the thyroid gland to the Antarctic environment was studied in nine healthy euthyroid tropical men of the Sixth Indian Antarctic Expedition during 1 year of their residence at polar latitudes. Circulatory concentrations of thyroid hormones, total T4 (TT4), total T3 (TT3), free T4 (FT4), free T3 (FT3), reverse T3 (rT3), thyroxine binding globulin (TBG), T3 uptake and thyroid stimulating hormone (TSH) were estimated in New Delhi and during the first week of each month of the stay in Antarctica. At the end of the Austral summer in March, the TT3 concentrations were found to be significantly lower (P < 0.01) compared to values recorded in New Delhi and showed a significant increase (P < 0.05) during the Austral winter in August. The mean TT3 concentrations from May to December were found to be significantly higher than the March or April values. Plasma TT4 and rT3 concentrations tended to decline in March but remained unaltered during the entire period in Antarctica. The FT4, FT3, TBG and T3 uptake did not show any appreciable change. Though, the TT3:TT4 ratio tended to decline in March and April suggesting decreased peripheral conversion of T4 to T3 as the possible mechanism for a decline in TT3 in March. physical exertion and prolonged exposure to extreme cold appeared to be the major contributory factors. The TSH concentration in March, April, November and December were found to be significantly higher than the New Delhi values. The morning as well as evening cortisol concentrations during the Austral winter were higher than the March values suggesting that cortisol rhythmicity was well maintained in Antarctica, albeit at a higher level. These observations indicated that the subtle changes in thyroid hormones during a prolonged stay at polar latitudes are related not only to the extreme cold but also to other factors such as physical activity, polar days and polar nights.

The annual cycle of the pituitary-thyroid axis activity in healthy men under prolonged cold air exposure

“…While the monthly studies did not reveal changes in the FT 3 and FT 4 levels during wintering, the authors have suggested that the serum TH levels during Antarctic wintering were affected by various factors of which the physical activity and the sharp change of day duration were the most significant. The TSH concentrations in March, April, November and December were found to be significantly higher than before wintering [21]. These data testify on our opinion about an important role of ethnic origin of the examined groups.…”

Different adaptations of Chinese winter-over expeditioners during prolonged Antarctic and sub-Antarctic residence

“…*P < 0.05, Great Wall Station versus Zhongshan Station Palinkas et al 2007a;Levy et al 2013), FT4 of the Zhongshan Station crew decreased during the austral winter. Concurrently, TSH levels increased gradually until return to China, where they became statistically significant, suggesting the presence of Polar T3 Syndrome (Sawhney et al 1995;Do et al 2004). The declining levels of FT3 and FT4 prompt the hypothalamic-pituitary-thyroid (HPT) axis to produce more TSH to stimulate the increased availability of these two hormones.…”

Transthyretin is not necessary for thyroid hormone metabolism in conditions of increased hormone demand

“…There are cases of humans with partial or total TBG deficiency, which results in euthyroid hypothyroxinemia (Refetoff 1989, Bartalena 1993. Even though exposure to cold is known to induce alteration in thyroid hormone metabolism in humans (Solter et al 1989, Sawhney et al 1995, Do et al 2004, to the best of our knowledge there are no reports on the ability of these individuals to adapt to cold. Because TTR-null mice are also euthyroid hypothyroxinemic, it is reasonable to believe that humans with TBG deficiency would normally adapt to cold.…”