title: Brown adipose tissue and seasonal variation in humans.
abstract: OBJECTIVE
  Brown adipose tissue (BAT) is present in adult humans where it may be important in the prevention of obesity, although the main factors regulating its abundance are not well established. BAT demonstrates seasonal variation relating to ambient temperature and photoperiod in mammals. The objective of our study was therefore to determine whether seasonal variation in BAT activity in humans was more closely related to the prevailing photoperiod or temperature.
  
  
  METHODS
  We studied 3,614 consecutive patients who underwent positron emission tomography followed by computed tomography scans. The presence and location of BAT depots were documented and correlated with monthly changes in photoperiod and ambient temperature.
  
  
  RESULTS
  BAT activity was demonstrated in 167 (4.6%) scans. BAT was demonstrated in 52/724 scans (7.2%) in winter compared with 27/1,067 (2.5%) in summer months (P < 0.00001, chi(2) test). Monthly changes in the occurrence of BAT were more closely related to differences in photoperiod (r(2) = 0.876) rather than ambient temperature (r(2) = 0.696). Individuals with serial scans also demonstrated strong seasonal variation in BAT activity (average standardized uptake value [SUV(max)] 1.5 in July and 9.4 in January). BAT was also more common in female patients (female: n = 107, 7.2%; male: n = 60, 2.8%; P < 0.00001, chi(2) test).
  
  
  CONCLUSIONS
  Our study demonstrates a very strong seasonal variation in the presence of BAT. This effect is more closely associated with photoperiod than ambient temperature, suggesting a previously undescribed mechanism for mediating BAT function in humans that could now potentially be recruited for the prevention or reversal of obesity.
authors.affiliation: Departments of Radiology and Nuclear Medicine, Queens Medical Centre, University Hospitals, Nottingham, U.K.
authors.forename: Iain T H
authors.initials: IT
authors.lastname: Au-Yong
authors.forename: Natasha
authors.initials: N
authors.lastname: Thorn
authors.forename: Rakesh
authors.initials: R
authors.lastname: Ganatra
authors.forename: Alan C
authors.initials: AC
authors.lastname: Perkins
authors.forename: Michael E
authors.initials: ME
authors.lastname: Symonds
mesh_terms: D002001:Adipose Tissue, Brown / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000517:prevention & control; D049268:Positron-Emission Tomography; D012621:Seasons; D013696:Temperature; D014057:Tomography, X-Ray Computed; D006113:United Kingdom; D055815:Young Adult
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