Abstract
F18-fluorodeoxyglucose (FDG)-positron emission tomography (PET) along with computed tomography (CT) is a standard method for assessing brown adipose tissue (BAT) activity. We tested the usefulness of near-infrared time-resolved spectroscopy (NIRTRS) as a simple and noninvasive method for evaluating BAT density (BAT-d) by examining the effects of some factors known to influence BAT activity. The total hemoglobin concentration as a parameter of BAT-d was evaluated using NIRTRS in the supraclavicular region in 413 Japanese individuals. The associations were analyzed between BAT-d and sex, age, the percentages of body fat (%BF), visceral fat (VF), and the seasonal ambient temperature (AmT) fluctuations. Age was associated with decreased BAT-d (P < 0.05). There was no sex difference in the BAT-d, except for those in their twenties. Multivariate analyses revealed that %BF and VF were correlated with BAT-d, and the lower AmT (around 4°C or 5°C) for 4 and 6 weeks prior to the measurement day was associated with an increase in the BAT-d. Our NIRTRS results were analogous to those reported with FDG18-PET / CT, indicating the usefulness of NIRTRS. BAT-d might increase during the 4 and 6 weeks after the AmT decreases to lower than 4°C or 5°C.
Highlights
Active brown adipose tissue (BAT) has been detected by 18Ffluorodeoxyglucose (FDG)–positron emission tomography (PET) combined with computed tomography (CT)[1,2,3,4] in adults and neonates, as well as animals
The univariate regression analysis showed that BAT density (BAT-d), age, and sex significantly was correlated with Body mass index (BMI), %BF, and visceral fat area (VFA), respectively (Table 2)
The multivariate regression analysis revealed that BAT-d and sex were determinants of BMI, %BF, and VFA, but age did not affect BMI (Table 2)
Summary
Active brown adipose tissue (BAT) has been detected by 18Ffluorodeoxyglucose (FDG)–positron emission tomography (PET) combined with computed tomography (CT)[1,2,3,4] in adults and neonates, as well as animals. Most epidemiological studies related to BAT have been informed by work in oncology and used 18FDG-PET∕CT in thermoneutral conditions. 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] 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. The measurements were conducted under thermoneutral conditions, wherein the FDG uptake might have been underestimated.[1,18] the 18FDG-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] 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 AmT11 and the other study stating that BAT activity was higher in early winter than late winter or early spring.[21]
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