Prevalence, Mass, and Glucose-Uptake Activity of 18F-FDG-Detected Brown Adipose Tissue in Humans Living in a Temperate Zone of Italy

Abstract

BackgroundThe 18F-fluorodeoxyglucose (18F-FDG)-detected brown adipose tissue (BAT), is enhanced by cold stimulus and modulated by other factors that still have to be disentangled. We investigated the prevalence, mass, and glucose-uptake activity of 18F-FDG-detected BAT in a population of adults living in the temperate climatic zone of the Rome area.Methods and FindingsWe retrospectively analyzed 6454 patients who underwent 18F-FDG positron emission tomography/computed tomography (PET/CT) examinations. We found 18F-FDG BAT in 217 of the 6454 patients (3.36%). Some of them underwent more than one scan and the positive scans were 278 among 8004 (3.47%). The prevalence of patients with at least one positive scan was lower in men (1.77%; 56 of 3161) compared with women (4.88%; 161 of 3293). The BAT positive patients were most frequently younger, thinner and with lower plasma glucose levels compared with BAT negative patients. The amount of BAT in the defined region of interest, the activity of BAT and the number of positive sites of active BAT were similar in both sexes. The prevalence of patients with 18F-FDG positive PET/CT was highest in December-February, lower in March-May and September-November, and lowest in June-August and was positively correlated with night length and negatively correlated with ambient temperature. Changes in day length and variations of temperature, associated with the prevalence of positive BAT patients. Among the patients who had multiple scans, outdoor temperature was significantly lower and day length was shorter on the occasion when BAT was detected.ConclusionsThis study identifies day length, outdoor temperature, age, sex, BMI, and plasma glucose levels as major determinants of the prevalence, mass, and activity of 18F-FDG-detected BAT.

Brown adipose tissue density measured by near-infrared time-resolved spectroscopy in Japanese, across a wide age range

“…6,[13][14][15][16][17]19,21 BAT activity was found to be higher in women, in many oncology studies. [13][14][15][16][17]20 However, no sex differences were found in 18 FDG-PET∕CT studies with cold exposure. 6,22 The oncology studies had very large sample sizes but did not include cold exposure, whereas the studies using 18 FDG-PET∕CT with cold exposure had relatively small sample sizes.…”

“…We showed that body fatness parameters were negatively correlated with BAT-d, which is consistent with the results of various studies that used 18 FDG-PET∕CT, regardless of the presence of cold exposure. 6,[14][15][16][17]19,20 Although we should consider the possibility that the BAT-d was affected by subcutaneous fat thickness, 26 the subcutaneous fat thickness in the supraclavicular region is within a very narrow range and has little effect on the measured parameters. For instance, the fat thickness in the supraclavicular region ranged from 0.6 to 2.5 mm when evaluated by B-mode ultrasonography in this study.…”

“…These data showed that BAT activity was higher in women, younger individuals, and lean patients, as well as under conditions of lower ambient temperatures (AmT). [11][12][13][14][15][16][17] However, since these data were collected for the diagnosis of cancer, data on healthy adults were lacking, and the mean age was biased toward patients older than 60 years of age. In addition, the measurements were conducted under thermoneutral conditions, wherein the FDG uptake might have been underestimated.…”

“…1,18 Indeed, the 18 FDG-PET∕CT-positive BAT ratio is variable; in studies involving cancer patients without cold exposure, the ratio was found to be extremely low (∼5%). [11][12][13][14][15][16][17]19,20 However, in younger healthy individuals, who were exposed to cold, the ratio was much higher (∼50% to 100%). 3,6 With regards to the effect of AmT on the activation of BAT, the results are conflicting with one study demonstrating that the rise in the BAT activity was delayed by a few months in association with a beginning in the decline in the AmT 11 and the other study stating that BAT activity was higher in early winter than late winter or early spring.…”

Prolonged daily light exposure increases body fat mass through attenuation of brown adipose tissue activity

“…The detectability of BAT by [ 18 F]fluorodeoxyglucose-PET-CT imaging at room temperature follows a circannual cycle, both in the northern and southern hemispheres (31)(32)(33), with low detectability of BAT in summer (i.e., short day) compared with winter (i.e., long day). Although differences in outside temperature over the year would be a likely explanation for this phenomenon, the detectability of BAT showed a stronger correlation with day length than with outside temperature (31).…”