Table 1

Important studies investigating BAT and its relevance for obesity and insulin sensitivity/glucose metabolism in humans

StudyDesignMain findings
Lee et al. 2010 (46)Retrospective analysis of 2,934 PET/CT scans; no cold stimulation usedPrevalence of BAT in 8.5% of all scans; detection of BAT inversely associated with age, BMI, and fasting glucose level
Ouellet et al. 2011 (42)Retrospective analysis of 4,842 PET/CT scans; no cold stimulation usedActive BAT in 6.8% of patients; highly significant inverse association with outdoor temperature, age, BMI, and diabetes status
Orava et al. 2011 (71)Prospective controlled study in 27 healthy volunteers (20 male, 7 female), using mild cold exposure (2 h at 17°C in light clothing) to stimulate BATGlucose uptake induced 12-fold in BAT by cold; induced fivefold in BAT by insulin
Ouellet et al. 2012 (40)Prospective controlled study in 6 healthy men using cold exposure by liquid-cooled suit and PET/CTIncreased glucose and nonesterized fatty acid uptake in BAT upon cold exposure; reduction in BAT triglyceride content after cold-induced thermogenesis, indicating consumption of intracellular lipids
Vijgen et al. 2012 (63)Prospective observational study in 10 patients undergoing bariatric surgery for morbid obesity (BMI 42 kg/m2 at baseline, 30 kg/m2 after weight loss); individual cooling by cold air, BAT detection by FDG PETActive BAT in 2 of 10 patients at baseline and in 5 of 10 patients after weight loss; BAT activity increased significantly after weight loss in those positive for BAT at baseline
Orava et al. 2013 (73)Prospective study in 27 lean (BMI 22.7 kg/m2) and 36 obese (BMI 38.1 kg/m2) individuals; mild cold exposure (2 h at 17°C in light clothing) to stimulate BAT PET/CTBAT glucose uptake to cold and insulin stimulation were twice as large in lean as in obese subjects; weight loss (15% of body weight) did not increase BAT volume or activity
Yoneshiro et al. 2013 (52)Prospective controlled study in 51 healthy men (24 years of age, BMI 22 kg/m2); 22 subjects without detectable BAT at baseline underwent repeated cold exposure (2 h/day at 17°C) or control for 6 weeks; BAT activity was assessed by FDG PETIncreased BAT activity and decreased body fat mass after “cold training”
Chondronikola et al. 2014 (72)Prospective controlled study in 12 male volunteers (7 BAT positive, 5 BAT negative), who underwent controlled cold exposure for 8 h using a water-cooled vest and blanket PET/CTCold exposure increased resting energy expenditure, whole-body glucose disposal, plasma glucose oxidation, and insulin sensitivity in BAT-positive subjects
Lee et al. 2014 (74)Prospective study in 5 healthy men; cold acclimatization by exposure to a controlled temperature environment for 1 month, with mild cold exposure to air at 19°C; PET/CTNo change in cold-induced thermogenesis, but increased insulin sensitivity after cold acclimatization
Blondin et al. 2014 (51)Prospective study in 6 healthy men; daily exposure to cold at 10°C using liquid-conditioned suit for 4 weeks, 2 h/day; PET/CT45% increase in BAT volume, 2.2-fold increase in BAT oxidative metabolism, and 37% increase in BAT glucose uptake