Thyroid hyperactivity with high thyroglobulin in serum despite sufficient iodine intake in chronic cold adaptation in an Arctic Inuit hunter population

Abstract

Objective: Adult man hosts brown adipose tissue with the capacity to consume energy and dissipate heat. This is essential for non-shivering thermogenesis and its activation depends on sympathetic activity and thyroid hormones. This led us to evaluate the impact of chronic cold exposure on thyroid activity and thyroid hormones in serum in Arctic residents. Design: Comparative, population-based study (nZ535) performed in Greenland. Methods: Hunters were compared with other men, and Inuit in remote settlements in East Greenland with no modern housing facilities were compared with the residents of the capital city in West Greenland and residents of a major town in East Greenland in a cross-sectional study. We used interview-based questionnaires, measured TSH, free thyroxine, free triiodothyronine (fT 3 ), thyroglobulin (TG) antibody and TG (a measure of thyroid activity) in serum, and iodine and creatinine in spot urine samples. Results: Serum TG was the highest among hunters (PZ0.009) and settlement dwellers (PZ0.001), who were most markedly exposed to cold, even though they had the highest urinary iodine excretion (hunters, P!0.001; settlement dwellers, P!0.001). Hunters and settlement dwellers also had the lowest fT 3 (hunters, P!0.001; settlement dwellers, P!0.001) after adjusting for gender, age, smoking habits, alcohol intake and iodine excretion in multivariate linear regression models. TSH was not influenced by measures of cold exposure (hunter, PZ0.36; residence, PZ0.91). Conclusions: Cold exposure influenced thyroid hormones and TG in serum in Arctic populations consistent with consumption of thyroid hormone and higher thyroid hormone turnover. Findings emphasise that changes in thyroid activity are essential in cold adaptation in Arctic residents.

Seasonal and socioeconomic influences on thyroid function among the Yakut (Sakha) of Eastern Siberia

“…Additional evidence of the “polar T3 syndrome” is provided by Andersen et al (). The authors measured serum thyroid hormones levels during the fall among Inuit groups of Greenland living in the capital, in a major town in a rural district, and in four settlements that lack modern housing facilities and roads.…”

Forty‐five year trends in overweight and obesity in an indigenous arctic inuit society in transition and spatiotemporal trends

“…Physical activity is common in the Arctic society as hunting and fishing are common leisure activities in the capital city. In addition, the Arctic environment causes exposure to cold that may keep brown adipose tissue active among Arctic inhabitants irrespective of the westernised life style (Andersen et al, ). This will limit the accumulation of adipose tissue in these individuals (Laurberg et al, ) and support a decrease in the incremental rates of overweight.…”

Seasonal variation in basal metabolic rates among the yakut (Sakha) of Northeastern Siberia

“…Some of the differences in seasonal patterns of metabolic rates among high latitude groups likely reflect variation in the severity of climate and differences in activity patterns and cold exposure during the winter months. Lifestyle variation within circumpolar communities has been found to moderate intra‐population variation in acclimatization to cold stress (Andersen et al, ; Levy et al, ).…”