The presence of UCP1 demonstrates that metabolically active adipose tissue in the neck of adult humans truly represents brown adipose tissue.

Classically, adult humans have been considered not to possess active brown adipose tissue (BAT). However, positron-emission-tomography has shown fluorodeoxyglucose uptake that is distributed in such a way (e.g., in the neck) that it would seem to be BAT. Until now this has not been supported by direct evidence that these areas truly represented BAT, that is, the presence of the BAT-unique uncoupling protein-1 (UCP1). Samples of adipose tissue from the neck of 35 patients undergoing surgery for thyroid diseases were obtained and analyzed. In 1/3 of the subjects (the younger and leaner), distinct islands composed of UCP1 immunoreactive brown adipocytes could clearly be discerned, accounting for up to 1/3 of all adipocytes. The brown-adipose islands were richly sympathetically innervated (indicating acute central control); adjacent white adipose areas were not. The capillary density was high, implying a high capacity for oxygen delivery. Cells with features of brown adipocyte precursors were found in pericapillary areas. These data demonstrate that human adults indeed possess BAT and thus imply possibilities of future therapeutic strategies for the treatment of obesity, including maintenance of brown adipocytes and stimulation of the growth of preexisting brown precursors.