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

Objective: Adult man hosts brown adipose tissue with the capacity to consume energy and dissipate heat. This is essential to 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 (n=535) performed in Greenland.Methods: Hunters were compared to other men, and Inuit in remote settlements in East Greenland with no modern housing facilities were compared to residents of the capital city in West Greenland and residents of the major town in East Greenland in a cross-sectional study. We used interview-based questionnaires, measured thyroid stimulating hormone (TSH), free thyroxine (fT4), free triiodo-thyronine (fT3), thyroglobulin antibody (TGAb) and thyroglobulin (TG; a measure of thyroid activity) in serum, and iodine and creatinine in spot urine samples.Results: Serum TG was highest among hunters (p=0.009) and settlement dwellers (p=0.001), who were the most markedly cold exposed, even though they had the highest urinary iodine excretion (hunters, p