title: Risk factors for variation in 25-hydroxyvitamin D₃ and D₂ concentrations and vitamin D deficiency in children.
abstract: BACKGROUND
  Vitamin D status is believed to be best indicated by serum 25-hydroxyvitamin D [25(OH)D; consisting of 25(OH)D₃ and 25(OH)D₂] that are obtained from different sources. Suboptimal vitamin D status is common and associated with adverse health outcomes.
  
  
  OBJECTIVE
  The objectives were to report the prevalence and risk factors of vitamin D deficiency and determine associations of characteristics that have been shown to relate to total 25(OH)D with 25(OH)D₃ and 25(OH)D₂ concentrations.
  
  
  METHODS
  The Avon Longitudinal Study of Parents and Children is a population-based contemporary birth cohort (children born in 1991-1992) from southwest England.
  
  
  METHODS
  Seven thousand five hundred sixty children with serum 25(OH)D₃ and 25(OH)D₂ concentrations measured at the mean age of 9.9 yr participated in the study.
  
  
  RESULTS
  Vitamin D deficiency [total 25(OH)D concentration <20 ng/ml] was common (29%). The main risk factors were winter season, less time spent outdoors, low socioeconomic position, nonwhite ethnicity, older age, more advanced puberty stage, and female gender. Although there were some common risk factors for lower 25(OH)D₃ and 25(OH)D₂ concentrations (age, gender, puberty stage, body mass index, physical activity, household income, maternal education), several characteristics were associated with 25(OH)D₃ only (ethnicity, vitamin D intake, time spent outdoors, and UVB protection score) and others with 25(OH)D₂ only (protein and carbohydrate intake, parent's social class, and housing tenure).
  
  
  CONCLUSIONS
  Vitamin D deficiency was common in this contemporary U.K. cohort. Despite some overlap, there are differences in potential confounding structures for associations of 25(OH)D₃ and 25(OH)D₂ with health outcomes. These should be accounted for in future studies.
authors.affiliation: Medical Research Council, Centre for Causal Analysis in Translational Epidemiology, School of Social and Community Medicine, University of Bristol, Oakfield House, 15-23 Oakfield Grove, Clifton, Bristol BS8 2BN, United Kingdom.
authors.forename: Anna-Maija
authors.initials: AM
authors.lastname: Tolppanen
authors.forename: Abigail
authors.initials: A
authors.lastname: Fraser
authors.forename: William D
authors.initials: WD
authors.lastname: Fraser
authors.forename: Debbie A
authors.initials: DA
authors.lastname: Lawlor
mesh_terms: D015652:25-Hydroxyvitamin D 2 / Q000097:blood*; D002112:Calcifediol / Q000097:blood*; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D004739:England / Q000453:epidemiology; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D015995:Prevalence; D011446:Prospective Studies; D011627:Puberty; D012307:Risk Factors; D012621:Seasons; D012720:Severity of Illness Index; D012737:Sex Factors; D012959:Socioeconomic Factors; D013472:Sunlight; D014808:Vitamin D Deficiency / Q000097:blood* / Q000453:epidemiology* / Q000208:ethnology
chemical_list: D015652:25-Hydroxyvitamin D 2; D002112:Calcifediol