title: Higher serum 25-hydroxyvitamin D levels in school-age children are inconsistently associated with increased calcium absorption.
abstract: BACKGROUND
  Increasing serum 25-hydroxyvitamin D (25-OHD) in adults may enhance calcium absorption (Ca-abs). There are few similar pediatric data leading to uncertainty about the optimal target for 25-OHD to maximize Ca-abs.
  
  
  OBJECTIVE
  Our objective was to evaluate the relationship between 25-OHD and Ca-abs in a large cohort of school-age children and adolescents.
  
  
  METHODS
  We evaluated data from 439 Ca-abs measurements performed using dual-tracer stable isotope techniques conducted at our center over a 15-yr period in 251 healthy children, 4.9-16.7 yr of age.
  
  
  RESULTS
  Serum 25-OHD ranged from 28 to 197 nmol/liter (mean 85 +/- 2 nmol/liter) (sem). Total Ca-abs (intake times fractional absorption) were significantly correlated to 25-OHD in the whole population (r = 0.16, P = 0.001). This relationship was closer in the 197 studies in early puberty (Tanner 2 or 3, r = 0.35, P < 0.001) and not significant in pre- or late pubertal subjects. For the whole population, fractional Ca-abs adjusted for calcium intake were slightly but significantly higher at 25-OHD of 28-50 nmol/liter (0.344 +/- 0.019) compared with 25-OHD of 50-80 nmol/liter (0.280 +/- 0.014) or 25-OHD greater than 80 nmol/liter (0.297 +/- 0.015, P < 0.01 for each), suggesting adaptation to moderately low 25-OHD values.
  
  
  CONCLUSIONS
  There is no consistent pattern of relationship between 25-OHD and either fractional or total calcium absorption in school-age children. However, there appears to be a modest calcium absorptive response to higher 25-OHD during early puberty.
authors.affiliation: United States Department of Agriculture/Agricultural Research Service, Children's Nutrition Research Center, Houston, Texas 77030, USA. sabrams@bcm.edu
authors.forename: Steven A
authors.initials: SA
authors.lastname: Abrams
authors.forename: Penni D
authors.initials: PD
authors.lastname: Hicks
authors.forename: Keli M
authors.initials: KM
authors.lastname: Hawthorne
mesh_terms: D000042:Absorption; D000293:Adolescent; D002118:Calcium / Q000378:metabolism / Q000493:pharmacokinetics*; D002136:Calcium, Dietary / Q000378:metabolism / Q000493:pharmacokinetics; D002648:Child; D002675:Child, Preschool; D004435:Eating / Q000502:physiology; D005260:Female; D006801:Humans; D007408:Intestinal Absorption / Q000502:physiology; D008297:Male; D011153:Population; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood / Q000378:metabolism
chemical_list: D002136:Calcium, Dietary; D014807:Vitamin D; C104450:25-hydroxyvitamin D; D002118:Calcium