Background: The role of thyroid hormones after cold exposure and subsequent BAT activation is largely unknown.
Objective: To investigate the relationship between cold induced brown adipose tissue (BAT) and thyroid hormones at baseline and after 2 hours cold exposure and relationship with body composition.
Design: Nineteen healthy subjects (7 males, 12 females) with mean age of 26 years (range: 21-35), BMI of 21.7 kg/m2 (range: 18.5-26.0) underwent 18F-FDG PET and whole-body calorimetry after 2 hours of cold exposure (~14.5°C) in a crossover design. Standardized uptake values (SUV-mean) of the region of interest was calculated. Blood metabolites were measured before and 2 hours after cold exposure. Body composition was determined by dual-energy-x-ray absorptiometry (DXA).
Results: 12 of 19 subjects were BAT positive. Subjects were divided into groups based on the presence (n=12) or absence (n=7) of BAT. Subjects with BAT had higher T3, FT3/FT4 compared with subjects without BAT. TSH was reduced and FT4 level was significant increased after acute cold exposure. There was a significant positive correlation between FT3 and lean body mass and resting energy expenditure (REE). EE change from baseline after cold exposure was significantly positive related with FT3 at baseline and 2 hours after cold exposure.
Conclusion: Circulating FT3 was higher in BAT positive subjects and was a stronger predictor of EE changes after cold exposure in healthy humans.