title: Fibroblast Growth Factor 23 Concentrations Reflect Sex Differences in Mineral Metabolism and Growth in Early Infancy.
abstract: BACKGROUND
  The role of fibroblast growth factor 23 (FGF23) in the regulation of mineral homeostasis in early life is inadequately understood. We aimed to explore the effects of vitamin D supplementation on serum FGF23 and to elucidate longitudinal changes in FGF23, in addition to studying its association with mineral metabolism in early infancy.
  
  
  METHODS
  Altogether 113 healthy infants received vitamin D3 10, 30 or 40 µg/day from age 0.5 to 3.0 months. Cord blood at birth and capillary blood samples at 3 months were analyzed for serum 25-hydroxyvitamin D, parathyroid hormone, phosphate, calcium and intact and C-terminal FGF23.
  
  
  RESULTS
  In repeated-measures ANCOVA, intact FGF23 concentration increased with time (p < 0.001) and C-terminal FGF23 decreased (p < 0.001). At 3 months, girls had a higher concentration of intact FGF23 (51 vs. 26 pg/ml, p < 0.001) and a greater increase over time (x0394;FGF23 intact 45 vs. 16 pg/ml, p = 0.001) than boys. Vitamin D did not affect serum intact or C-terminal FGF23 concentrations. Girls showed a positive correlation between phosphate and intact FGF23 (p = 0.004), whereas in boys phosphate and C-terminal FGF23 correlated inversely (p = 0.006).
  
  
  CONCLUSIONS
  A substantial sex-related difference in intact FGF23 concentration exists during early infancy, possibly related to differences in skeletal growth between boys and girls.
authors.affiliation: Children's Hospital, University of Helsinki and Helsinki University Hospital, Helsinki, Finland.
authors.forename: Elisa
authors.initials: E
authors.lastname: Holmlund-Suila
authors.forename: Heli
authors.initials: H
authors.lastname: Viljakainen
authors.forename: Östen
authors.initials: Ö
authors.lastname: Ljunggren
authors.forename: Timo
authors.initials: T
authors.lastname: Hytinantti
authors.forename: Sture
authors.initials: S
authors.lastname: Andersson
authors.forename: Outi
authors.initials: O
authors.lastname: Mäkitie
mesh_terms: D002762:Cholecalciferol / Q000008:administration & dosage*; D019587:Dietary Supplements; D005260:Female; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000097:blood*; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D010710:Phosphates / Q000097:blood*; D012727:Sex Characteristics
chemical_list: C000717427:FGF23 protein, human; D010710:Phosphates; D002762:Cholecalciferol; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23