title: Early physical activity provides sustained bone health benefits later in childhood.
abstract: OBJECTIVE
  This study examined the potential effect of early childhood moderate and vigorous physical activity (MVPA) on later bone health.
  
  
  METHODS
  Three hundred and thirty-three children, participating in the Iowa Bone Development Study, were studied at ages 5, 8, and 11 yr. MVPA (min x d(-1)) was measured using an accelerometry-based physical activity monitor. Bone mineral content (BMC; g) of the whole body, lumbar spine, and hip was measured using dual-energy x-ray absorptiometry. Mixed regression models were used to test whether MVPA at age 5 yr had an effect on BMC at ages 8 and 11 yr after adjustment for concurrent height, weight, age, maturity, and MVPA. The analysis was repeated to control for bone outcomes at age 5 yr. Mixed-model least-squares mean values at the person level of covariates for age group were used to compare the BMC at ages 8 and 11 yr of children in the highest and lowest quartiles of MVPA at age 5 yr.
  
  
  RESULTS
  For boys and girls, MVPA at age 5 yr predicted BMC adjusted for concurrent height, weight, age, maturity, and MVPA at ages 8 and 11 yr (P < 0.05). When the analysis was repeated to also control for BMC at age 5 yr, the effect of MVPA at age 5 yr was significant for boys but not for girls. Boys and girls in the highest quartile of MVPA at age 5 yr had 4%-14% more BMC at ages 8 and 11 yr than those in the lowest quartile of MVPA at age 5 yr (P < 0.05).
  
  
  CONCLUSIONS
  These results provide support for the benefits of early MVPA on sustained bone health during childhood especially for boys. Results indicate the importance of increasing MVPA as a strategy to improve BMC later in childhood.
authors.affiliation: Department of Health and Sport Studies, The University of Iowa, Iowa City, IA 52242, USA. kathleen-janz@uiowa.edu
authors.forename: Kathleen F
authors.initials: KF
authors.lastname: Janz
authors.forename: Elena M
authors.initials: EM
authors.lastname: Letuchy
authors.forename: Julie M
authors.initials: JM
authors.lastname: Eichenberger Gilmore
authors.forename: Trudy L
authors.initials: TL
authors.lastname: Burns
authors.forename: James C
authors.initials: JC
authors.lastname: Torner
authors.forename: Marcia C
authors.initials: MC
authors.lastname: Willing
authors.forename: Steven M
authors.initials: SM
authors.lastname: Levy
mesh_terms: D015519:Bone Density / Q000502:physiology*; D002648:Child; D002657:Child Development / Q000502:physiology; D002675:Child, Preschool; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D018670:Monitoring, Ambulatory; D011446:Prospective Studies; D012737:Sex Factors