Outdoor Temperature, Age, Sex, Body Mass Index, and Diabetic Status Determine the Prevalence, Mass, and Glucose-Uptake Activity of 18F-FDG-Detected BAT in Humans

Abstract

Context: In humans, the prevalence, mass, and glucose-uptake activity of 18F-fluorodeoxyglucose (18F-FDG)-detected brown adipose tissue (BAT), which are expectedly enhanced by a cold stimulus, also appear modulated by other factors that still have to be disentangled. Objective: The objective of the study was to investigate the factors determining the prevalence, mass, and glucose-uptake activity of 18F-FDG-detected BAT in humans. Research Design and Methods: We retrospectively analyzed all 18F-FDG positron emission tomography/computed tomography examinations performed between January 2007 and December 2008 at our institution for 18F-FDG uptake within the cervical/supraclavicular, mediastinal, paravertebral, and perirenal fat areas. The influence of outdoor temperature, sex, age, body mass index (BMI), plasma glucose level, diabetes diagnosis, day length, and cancer status on the prevalence, mass, and glucose-uptake activity of 18F-FDG-detected BAT depots was investigated. Results: Three hundred twenty-eight of the 4842 patients (6.8%) had 18F-FDG-detected BAT. The prevalence of 18F-FDG BAT was negatively associated with outdoor temperature (P < 0.0001), age (P < 0.0001), BMI (P < 0.0001), and diabetes status (P = 0.0003). Moreover, there was a significant age × sex interaction for the prevalence of 18F-FDG BAT (the younger the subjects, the greater the sex difference). The mass and glucose-uptake activity of 18F-FDG-detected BAT also decreased with increasing outdoor temperature (P < 0.0001), age (P < 0.0001), and BMI (P < 0.0001). They were lower in men than in women (P < 0.001) and lower in diabetic than in nondiabetic patients (P = 0.0002). Conclusions: The present study identifies outdoor temperature, age, sex, BMI, and diabetes status as determinants of the prevalence, mass, and glucose-uptake activity of 18F-FDG-detected BAT.