Background: Cold stimulation of human brown adipose tissue (BAT) can increase its glucose uptake and energy expenditure, making it a potential target for treating obesity and metabolic disease. BAT is commonly found in deeper fascial layers of specific depots. We observed a distinct sexual dimorphism in the dorsal side of the cervical BAT depot.

Methods: Twenty-one healthy, lean, young subjects (12 men, mean BMI 23 ± 2.1 kg/m2), were exposed to five hours of tolerable cold exposure. BAT was measured via by 18F-FDG PET/CT.

Results: Men and women had similar total BAT metabolic activity. We classified the cervical BAT depot into two distinct anatomically continuous areas: a deeper, intermuscular region, and a superficial, dorsocervical region (sdBAT, Figure A-B), sdBAT was present in 6 women, but only in one man (Figure C). Women had less lean mass than men (p<0.001). In women, individual sdBAT metabolic activity was negatively correlated with lean body mass (p=0.05) and positively correlated with total and cervical BAT (p≤0.04).

Conclusions: We believe that sdBAT in women is likely part of the same fascial layer as the classical cervical depot. But based on its location, the sdBAT depot could be a remnant of interscapular BAT seen in rodents and human newborns. These findings are consistent with a model in which the dominant source of thermogenesis is lean tissue, which is lower in women, and when insufficient leads to BAT activation.

L. Fletcher: None. B. Leitner: None. K.I. Kim: None. S. McGehee: None. R. Brychta: None. A. Cypess: None. K.Y. Chen: None.

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