Association of objectively measured physical activity with brown adipose tissue volume and activity in young adults

Purpose: Human brown adipose tissue (BAT) has gained considerable attention as a potential therapeutic target for obesity and type 2 diabetes; however, whether physical activity (PA) might be an efficient stimulus to activate and recruit BAT remains to be ascertained. We aimed to examine whether objectively measured PA levels were associated with BAT volume and activity in young sedentary adults. We additionally examined the association of PA levels with the skeletal muscles activity. Methods: A total of 130 young healthy and sedentary adults (67% women; age, 21.9 ± 2.1 years old; body mass index, 25 ± 4.8 kg/m2) participated in this cross-sectional study. PA was objectively measured with a wrist-worn accelerometer for 7 consecutive days. Age-specific cut points were applied to classify wrist accelerations into sedentary time and different PA intensities (i.e., light, moderate, vigorous, moderate-vigorous). The participants underwent 2 hours of a personalized cold exposure to determine the cold-induced BAT volume and activity and the skeletal muscles activity by means of an 18F-fluorodeoxyglucose positron emission tomography combined with a CT scan. Results: Objectively measured PA intensity levels were neither associated with BAT volume and activity nor with the skeletal muscles activity (all P > 0.05). The results remained after adjusting for sex, waking time, and environmental temperature. Conclusions: Although PA plays an important role in the prevention of obesity and related comorbidities, it seems that other physiological mechanisms rather than brown adipocyte activation or recruitment might moderate its beneficial metabolic effects in young sedentary adults.