title: Effects of birth cohort and age on body composition in a sample of community-based elderly.
abstract: BACKGROUND
  The effect of the recent obesity epidemic on body composition remains unknown. Furthermore, age-related changes in body composition are still unclear.
  
  
  OBJECTIVE
  The objective was to simultaneously examine the effects of birth cohort and age on body composition.
  
  
  METHODS
  A total of 1786 well-functioning, community-based whites and blacks (52% women and 35% blacks) aged 70-79 y from the Health, Aging, and Body Composition Study underwent dual-energy X-ray absorptiometry annually from 1997 to 2003.
  
  
  RESULTS
  At baseline, mean +/- SD percentage body fat, fat mass, and lean mass (bone-free) were 28 +/- 5%, 24 +/- 7 kg, and 56 +/- 7 kg, respectively, for men and 39 +/- 6%, 28 +/- 9 kg, and 40 +/- 6 kg for women. Mixed models were used to assess the effects of cohort and age-related changes on body composition. Later cohorts in men had a greater percentage body fat (0.32% per birth year, P < 0.0001) than did earlier cohorts. This cohort effect was due to a greater increase in fat mass than in lean mass (0.45 kg and 0.17 kg/birth year, respectively). With increasing age, percentage body fat in men initially increased and then leveled off. This age-related change was due to an accelerated decrease in lean mass and an initial increase and a later decrease in fat mass. Similar but less extreme effects of cohort and age were observed in women.
  
  
  CONCLUSIONS
  The combination of effects of both birth cohort and age leads to bigger body size and less lean mass in the elderly.
authors.affiliation: Sticht Center on Aging, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA. jding@wfubmc.edu
authors.forename: Jingzhong
authors.initials: J
authors.lastname: Ding
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Kritchevsky
authors.forename: Anne B
authors.initials: AB
authors.lastname: Newman
authors.forename: Dennis R
authors.initials: DR
authors.lastname: Taaffe
authors.forename: Barbara J
authors.initials: BJ
authors.lastname: Nicklas
authors.forename: Marjolein
authors.initials: M
authors.lastname: Visser
authors.forename: Jung Sun
authors.initials: JS
authors.lastname: Lee
authors.forename: Michael
authors.initials: M
authors.lastname: Nevitt
authors.forename: Frances A
authors.initials: FA
authors.lastname: Tylavsky
authors.forename: Susan M
authors.initials: SM
authors.lastname: Rubin
authors.forename: Marco
authors.initials: M
authors.lastname: Pahor
authors.forename: Tamara B
authors.initials: TB
authors.lastname: Harris
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D001823:Body Composition / Q000502:physiology*; D049628:Body Size / Q000502:physiology; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male