Anatomical Locations of Human Brown Adipose Tissue: Functional Relevance and Implications in Obesity and Type 2 Diabetes

We will review information about and present hypotheses as to the anatomy of brown adipose tissue (BAT). Why is it located where it is in humans? Its anatomical distribution is likely to confer survival value by protecting critical organs from hypothermia by adaptive thermogenesis. Ultimately, the location and function will be important when considering therapeutic strategies for preventing and treating obesity and type 2 diabetes, in which case successful interventions will need to have a significant effect on BAT function in subjects living in a thermoneutral environment. In view of the diverse locations and potential differences in responsiveness between BAT depots, it is likely that BAT will be shown to have much more subtle and thus previously overlooked functions and regulatory control mechanisms.Until ~10 years ago, brown adipose tissue (BAT) was considered to be biologically active in neonates and young children generating heat during cold exposure by adaptive thermogenesis to maintain normal body temperature (1). BAT regressed with aging by transforming into white adipose tissue (WAT) (2), and BAT in adults was not considered important in energy metabolism (1,3). At that time, reports in the nuclear medicine literature surfaced that ¹⁸F-fluorodeoxyglucose (FDG), an intravenously administered radioactive glucose analog taken up but not metabolized by neoplasms and used to delineate metastatic cancers in positron emission tomography (PET) scans, also localized in adipose tissues pinpointed by concomitant computed tomography (CT) (PET-CT fusion) scans to be commensurate with BAT and in most instances not with tumor tissue (4,5). It was therefore demonstrated that the main BAT depot was within the supraclavicular region, although as detailed below a number of perhaps less important depots were identified (6–11). Because more attention has been given to the physiology (6–9), pathophysiology (6), and clinical characteristics (10,11) of human BAT rather than its anatomy, the purpose of this Perspective is to review information about and to consider hypotheses why BAT is located where it is in humans as well as the functional relevance and therapeutic implications of its locations.