1 E Merchán Ramírez, Physical and Sports Education, University of Granada, Granada, 18016, Spain
2 G Sanchez-Delgado, Department of Physical, Pennington Biomedical Research Center, Baton Rouge, United States
3 C Arrizabalaga-Arriazu, Department of Endocrinology, Fundación Hospital de Jove, Gijon, Spain
4 B Martinez-Tellez, Department of Physical, University of Granada, Granada, 18071, Spain
5 A Mendez-Gutierrez, 5Department of Biochemistry and Molecular Biology II, Institute of Nutrition and Food Technology "José Mataix," Center of Biomedical Research, University of Granada, Granada, Spain
6 M Muñoz-Torres, Bone Metabolic Unit (RETICEF). Endocrinology Division., Hospital Universitario San Cecilio, Granada, 18012, Spain
7 J Llamas-Elvira, Nuclear Medicine Service, Nuclear Medicine Services "Virgen de las Nieves" University Hospital, Granada, Spain
8 J Ruiz, 1PROFITH "PROmoting FITness and Health through Physical Activity" Research Group, Department of Physical and Sports Education, Sport and Health University Research Institute (iMUDS), Faculty of Sports Science., University of Granada, Granada, Spain
Purpose: Thyroid hormones (THs) are important mediators of brown adipose tissue (BAT) differentiation. However, the association of TH concentrations with human BAT is unclear. The present work examines the associations between circulating thyroid-stimulating hormone (TSH) and THs concentrations (i.e. free tri-iodothyronine, FT3, and free thyroxine, FT4), under thermoneutral [22-23ºC] and cold-induced conditions, and BAT volume, 18F-fluorodeoxyglucose (18F-FDG) uptake and mean radiodensity.
Methods: A total of 106 young healthy, euthyroid adults (34 men/72 women; 22.0 ± 2.1 years old; 24.9 ± 4.6 kg/m2) participated in this cross-sectional study. BAT volume, 18F-FDG uptake and mean radiodensity were assessed after 2 h of personalized (i.e., contemplating each individual's shivering threshold) cold exposure via positron emission tomography/computerized tomography (PET/CT) static scanning. TSH and THs levels were determined before (thermoneutral) and 1 h after the cold exposure.
Results: Cold exposure increased circulating FT4 (P=0.038) and reduced of TSH levels (P≤0.001). Conversely, the FT3 serum concentration was not modified by cold exposure (P=0.435). No associations were found between the TSH and THs thermoneutral (all P>0.289) or cold-induced levels (all P>0.067) and BAT volume,18F-FDG uptake and mean radiodensity. These findings were independent of sex and body mass index.
Conclusions: Thyroid function is modulated by cold exposure, yet it is not associated with BAT volume or glucose metabolism assessed after 2h of cold exposure in young healthy, euthyroid adults.