title: 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 likely, 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.
  
  
  METHODS
  Data from 260 subjects (98 with BAT and 162 study date-matched control subjects) 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 activity and BAT mass were higher in female (1.59 +/- 0.10 and 32 +/- 5 g vs. 1.02 +/- 0.10 and 18 +/- 4 g, both P < or = 0.0006) than in male subjects. In multivariate analyses, sex (P < 0.0001), age (P < 0.0001), and BMI (P = 0.0018) were associated independently with BAT activity. Interestingly, only in male subjects was there an interaction between BMI and age in determining BAT activity (P = 0.008) and BAT mass (P = 0.0002); BMI decreased with increasing BAT activity and BAT mass in the lowest age tertile (Spearman rank correlation coefficient r(s) = -0.38, P = 0.015 and r(s) = -0.37, P = 0.017, respectively), not in the higher age tertiles. Furthermore, BAT activity and mass differed between female and male subjects only in the upper two age tertiles (all P < or = 0.09).
  
  
  CONCLUSIONS
  Our data corroborate that, in general, BAT activity and BAT mass are elevated in female subjects and in younger people. Importantly, we provide novel evidence that the impact of BAT activity and BAT mass on adiposity appears to decline with aging only in male subjects. Furthermore, while BAT activity and BAT mass only moderately decline with increasing age in female subjects, a much stronger effect is found in male subjects.
authors.affiliation: Department of Diagnostic and Interventional Radiology, University of Tübingen, Tübingen, Germany.
authors.forename: Christina
authors.initials: C
authors.lastname: Pfannenberg
authors.forename: Matthias K
authors.initials: MK
authors.lastname: Werner
authors.forename: Sabine
authors.initials: S
authors.lastname: Ripkens
authors.forename: Irina
authors.initials: I
authors.lastname: Stef
authors.forename: Annette
authors.initials: A
authors.lastname: Deckert
authors.forename: Maria
authors.initials: M
authors.lastname: Schmadl
authors.forename: Matthias
authors.initials: M
authors.lastname: Reimold
authors.forename: Hans-Ulrich
authors.initials: HU
authors.lastname: Häring
authors.forename: Claus D
authors.initials: CD
authors.lastname: Claussen
authors.forename: Norbert
authors.initials: N
authors.lastname: Stefan
mesh_terms: D002001:Adipose Tissue, Brown / Q000000981:diagnostic imaging* / Q000378:metabolism*; D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001823:Body Composition / Q000502:physiology; D015992:Body Mass Index; D002648:Child; D004734:Energy Metabolism / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography; D012016:Reference Values; D012737:Sex Factors; D018709:Statistics, Nonparametric