Impact of Age on the Relationships of Brown Adipose Tissue with Sex and Adiposity in Humans

Abstract Objective: Brown adipose tissue (BAT) regulates energy homeostasis and fat mass in mammals and newborns and, most probably, in adult humans. Because BAT activity and BAT mass decline with age in humans, the impact of BAT on adiposity may decrease with aging. In the present study we addressed this hypothesis, and further investigated the effect of age on the sex differences in BAT activity and BAT mass. Materials and Methods: Data from 260 subjects (98 with BAT and 162 study date-matched controls) who underwent 18 F-fluorodeoxyglucose positron-emission tomography/computed tomography ( 18 F-FDG PET/CT) under thermoneutral conditions were analyzed. BAT activity and BAT mass were determined in the upper body. Results: BAT activityand BAT mass were higher in females (1.59±0.10 and 32±5 g vs 1.02±0.10 and 18±4 g, both p≤0.0006) compared to males. In multivariate analyses, sex (p s =−0.38, p=0.015 and r s =−0.37, p=0.017, respectively) but not in the higher age tertiles. Furthermore, BAT activityand massdiffered between females and males only in the upper two age tertiles (all p≤0.09). Conclusions: Our data corroborate that, in general, BAT activity and BAT mass are elevated in females and in younger people. Importantly, we provide novel evidence that only in males the impact of BAT activity and BAT mass on adiposity appears to decline with aging. Furthermore, while with increasing age BAT activity and BAT mass merely moderately decline in females, a much stronger effect is found in males.