Abstract
Thyroid hormones (TH) control brown adipose tissue (BAT) activation and differentiation, but their subsequent homeostatic response following BAT activation remains obscure. This study aimed to investigate the relationship between cold- and capsinoids-induced BAT activation and TH changes between baseline and 2 hours post-intervention. Nineteen healthy subjects underwent 18F-fluorodeoxyglucose positron-emission tomography (18F-FDG PET) and whole-body calorimetry (WBC) after 2 hours of cold exposure (~14.5 °C) or capsinoids ingestion (12 mg) in a crossover design. Standardized uptake values (SUV-mean) of the region of interest and energy expenditure (EE) were measured. Plasma free triiodothyronine (FT3), free thyroxine (FT4) and thyroid stimulating hormone (TSH) were measured before and 2 hours after each intervention. Subjects were divided into groups based on the presence (n = 12) or absence (n = 7) of BAT after cold exposure. 12 of 19 subjects were classified as BAT-positive. Subjects with BAT had higher baseline FT3 concentration, baseline FT3/FT4 ratio compared with subjects without BAT. Controlling for body fat percentage, FT3 concentration at baseline was associated with EE change from baseline after cold exposure (P = 0.037) and capsinoids (P = 0.047). Plasma FT4 level significantly increased associated with reciprocal decline in TSH after acute cold exposure and capsinoids independently of subject and treatment status. Circulating FT3 was higher in BAT-positive subjects and was a stronger predictor of EE changes after cold exposure and capsinoids in healthy humans. BAT activation elevates plasma FT4 acutely and may contribute towards augmentation of thermogenesis via a positive feedback response.
Highlights
Thyroid hormones (TH) including triiodothyronine (T3) and thyroxine (T4) have long been well established to play an important role in energy expenditure (EE) and basal metabolic rate[1]
We found that EE was significantly increased after cold exposure and capsinoid ingestion in brown adipose tissue (BAT)-positive subjects assessed through 18F-FDG PET19
Following the 18F-FDG uptake post-cold exposure measured by calculating mean SUV, the subjects were divided into two groups: those with no detectable 18F-FDG uptake (BAT-negative, n = 7) and those with detectable 18F-FDG uptake with mean SUV ≥ 2 (BAT-positive; n = 12)
Summary
Thyroid hormones (TH) including triiodothyronine (T3) and thyroxine (T4) have long been well established to play an important role in energy expenditure (EE) and basal metabolic rate[1]. While the sympathetic response of BAT depends on TRα, Ribeiro et al.[9] reported that TRβ is required for UCP-1 dependent adaptive thermogenesis in BAT of mice that underscored the importance of TH for BAT function. We found that EE was significantly increased after cold exposure and capsinoid ingestion in BAT-positive subjects assessed through 18F-FDG PET19. This can be attributed purely to BAT activation, might the thyroid contributed to the persistence and maintenance of EE elevation via TH? To gain further insights regarding BAT activation effects on TH and vice versa in adult humans, this study evaluated TH changes after cold and capsinoids exposure in BAT-positive and BAT-negative healthy participants. The relationship between BAT and TH before and after cold and capsinoids exposure were evaluated
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
