title: Tracking of bone mass and density during childhood and adolescence.
abstract: BACKGROUND
  Whether a child with low bone mineral density (BMD) at one point in time will continue to have low BMD, despite continued growth and maturation, is important clinically. The stability of a characteristic during growth is referred to as "tracking."
  
  
  OBJECTIVE
  We examined the degree of tracking in bone mineral content (BMC) and BMD during childhood and adolescence and investigated whether tracking varied according to age, sexual maturation, and changes in growth status.
  
  
  METHODS
  We conducted a longitudinal study with measurements at baseline and annually for 3 yr.
  
  
  METHODS
  The Bone Mineral Density in Childhood Study was conducted at five clinical centers in the United States.
  
  
  METHODS
  A total of 1554 girls and boys, ages 6-16 yr at baseline, participated in the study.
  
  
  METHODS
  Whole body, spine, hip, and forearm BMC and BMD were measured by dual-energy x-ray absorptiometry, and age-, sex-, and race-specific Z-scores were calculated. Deviation from tracking was calculated as the Z-score at yr 3 minus baseline.
  
  
  RESULTS
  Correlations between Z-scores at baseline and yr 3 ranged from 0.76-0.88. Among children with a Z-score below -1.5 at baseline, 72-87% still had a Z-score below -1 after 3 yr. Age, sexual maturation, and deviations in growth status (P < 0.01) were associated with deviation from tracking; however, tracking was strongly evident even after adjusting for the effects of age, maturation, and growth.
  
  
  CONCLUSIONS
  Bone density showed a high degree of tracking over 3 yr in children and adolescents. Healthy children with low bone density will likely continue to have low bone density unless effective interventions are instituted.
authors.affiliation: Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio 45229, USA. heidi.kalkwarf@cchmc.org
authors.forename: Heidi J
authors.initials: HJ
authors.lastname: Kalkwarf
authors.forename: Vicente
authors.initials: V
authors.lastname: Gilsanz
authors.forename: Joan M
authors.initials: JM
authors.lastname: Lappe
authors.forename: Sharon
authors.initials: S
authors.lastname: Oberfield
authors.forename: John A
authors.initials: JA
authors.lastname: Shepherd
authors.forename: Thomas N
authors.initials: TN
authors.lastname: Hangartner
authors.forename: Xangke
authors.initials: X
authors.lastname: Huang
authors.forename: Margaret M
authors.initials: MM
authors.lastname: Frederick
authors.forename: Karen K
authors.initials: KK
authors.lastname: Winer
authors.forename: Babette S
authors.initials: BS
authors.lastname: Zemel
mesh_terms: D015502:Absorptiometry, Photon; D000293:Adolescent; D001827:Body Height / Q000502:physiology; D001835:Body Weight / Q000502:physiology; D015519:Bone Density / Q000502:physiology*; D001846:Bone Development / Q000502:physiology*; D001842:Bone and Bones / Q000033:anatomy & histology*; D002648:Child; D005260:Female; D005272:Femur Neck / Q000737:chemistry / Q000254:growth & development; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D009929:Organ Size / Q000502:physiology; D011884:Radius / Q000737:chemistry / Q000254:growth & development; D012044:Regression Analysis; D012741:Sexual Maturation; D013131:Spine / Q000737:chemistry / Q000254:growth & development