title: Physical activity, calcium intake, and bone mineral content in children in The Netherlands.
abstract: OBJECTIVE
  To examine the relation between physical activity, calcium intake, and bone mineral content in children.
  
  
  METHODS
  Population based, cross sectional study.
  
  
  METHODS
  Primary schools in Zoetermeer, The Netherlands.
  
  
  METHODS
  Altogether 1359 Dutch boys and girls, aged 7 to 11 years (response rate 88%).
  
  
  METHODS
  Bone mineral content was measured by quantitative roentgen microdensitometry of the midphalanx of the second digit at the diaphyseal and metaphyseal site. Maximal exercise testing, according to the Bruce treadmill protocol, was used to assess physical fitness. Habitual physical activity was assessed by use of a questionnaire on physical activities. Daily calcium intake from dairy products was estimated by use of a semiquantitative food frequency questionnaire.
  
  
  RESULTS
  Bone mineral content in boys was not linearly associated with physical fitness after adjustments for differences in height, body weight, chronological age, and skeletal age. In girls a linear association was found at the metaphyseal site only. When extreme groups were compared, bone mineral content was found to be higher in "high fitness children" (upper decile) than "low fitness children" (lowest decile), with statistical significance reached in boys only. When analyses were performed in subgroups of skeletal age, a clear linear relation between physical fitness and bone mineral content was seen in the mature subgroup in both boys and girls. No linear association was found between habitual physical activity and bone mineral content, while the results in extreme groups (that is, upper versus lowest decile) and in subgroups of skeletal age were comparable to those on physical fitness in boys only. No association was found between daily calcium intake and bone mineral content in this age group.
  
  
  CONCLUSIONS
  This cross sectional study in children aged 7 to 11 years suggests that an increased bone mineral content is found only in those with a high level of physical activity. This association is most pronounced in the more mature children. No evidence was found for an association between daily calcium intake and bone mineral content in childhood.
authors.affiliation: Department of Epidemiology and Biostatistics, Erasmus University Medical School, Rotterdam, The Netherlands.
authors.forename: M F
authors.initials: MF
authors.lastname: VandenBergh
authors.forename: S A
authors.initials: SA
authors.lastname: DeMan
authors.forename: J C
authors.initials: JC
authors.lastname: Witteman
authors.forename: A
authors.initials: A
authors.lastname: Hofman
authors.forename: W T
authors.initials: WT
authors.lastname: Trouerbach
authors.forename: D E
authors.initials: DE
authors.lastname: Grobbee
mesh_terms: D000365:Age Determination by Skeleton; D015519:Bone Density / Q000502:physiology*; D002136:Calcium, Dietary / Q000008:administration & dosage*; D002648:Child; D003430:Cross-Sectional Studies; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009426:Netherlands / Q000453:epidemiology; D010809:Physical Fitness; D012737:Sex Factors
chemical_list: D002136:Calcium, Dietary