title: Parathyroid hormone-ionized calcium dynamics over the first year of life.
abstract: BACKGROUND
  Ionized calcium (iCa) is believed to be the principle determinant of parathyroid hormone concentration (PTH). However, previous studies contained few infants.
  
  
  METHODS
  This ancillary study from our vitamin D3 dose-response trial in healthy, breastfed infants measured calcium, phosphorus, PTH and 25(OH)D (25-hydroxyvitamin D) at 1, 2, 3, 6, 9 and 12 months of age. The relationship between iCa and PTH was assessed by Pearson correlation and a mixed effects regression model to account for repeated measures.
  
  
  RESULTS
  No significant correlations were observed between iCa and PTH at individual visits (p>0.2). After accounting for repeated measures, PTH decreased with increasing iCa (slope -5.25; 95% confidence intervals (CI) -8.78 to -1.73), decreased with increasing 25(OH)D (slope -0.006; 95% CI -0.009 to -0.002, and increased with later visits (6-12 months, p<0.001), CONCLUSIONS: We observed a weak negative relationship between iCa and PTH and an increase with age consistent with physiologic maturation.
authors.forename: Atul K
authors.initials: AK
authors.lastname: Sharma
authors.forename: Sina
authors.initials: S
authors.lastname: Gallo
authors.forename: Catherine A
authors.initials: CA
authors.lastname: Vanstone
authors.forename: Sherry
authors.initials: S
authors.lastname: Agellon
authors.forename: Mary
authors.initials: M
authors.lastname: L'Abbé
authors.forename: Ali
authors.initials: A
authors.lastname: Khamessan
authors.forename: Kathryn
authors.initials: K
authors.lastname: Comeau
authors.forename: Hope A
authors.initials: HA
authors.lastname: Weiler
authors.forename: Celia
authors.initials: C
authors.lastname: Rodd
mesh_terms: D000367:Age Factors; D002118:Calcium / Q000097:blood*; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D010281:Parathyroid Hormone / Q000097:blood*; D011446:Prospective Studies
chemical_list: D010281:Parathyroid Hormone; D002118:Calcium