title: Relationships among vitamin D levels, parathyroid hormone, and calcium absorption in young adolescents.
abstract: BACKGROUND
  Evidence suggests that vitamin D status in adults, as assessed by serum 25-hydroxyvitamin D (25-OHD), is positively associated with calcium absorption fraction and inversely associated with serum PTH. Few comparable pediatric data exist.
  
  
  OBJECTIVE
  The objective of this study was to evaluate the relationships among vitamin D status, PTH, and calcium absorption in midpubertal boys and girls.
  
  
  METHODS
  Calcium absorption was measured as part of an evaluation of the effects of prebiotics (inulin-type fructans) using a stable isotope method in 93 young adolescents, 12.7 +/- 1.0 yr of age, receiving diets averaging approximately 900 mg/d calcium.
  
  
  RESULTS
  A significant positive relation to calcium absorption was found for serum 1,25-dihydroxyvitamin D (P = 0.048) and PTH (P = 0.007), but not for 25-OHD (P = 0.77). PTH was significantly inversely related to 25-OHD and was positively related to serum 1,25-dihydroxyvitamin D and osteocalcin. PTH was marginally significantly inversely related to lumbar spinal, but not whole body, bone mineral density.
  
  
  CONCLUSIONS
  These data suggest that in adolescents, especially in the presence of vitamin D insufficiency, PTH secretion increases to adapt to higher rates of bone formation associated with growth. This results in higher serum 1,25(OH)2D concentrations and increased calcium absorption results. Vitamin D status, as reflected by the serum 25-OHD level, is not closely related to calcium absorption. Whether adaptation to low serum 25-OHD is adequate under physiologically stressful situations, including those leading to very low serum 25-OHD levels, is unknown.
authors.affiliation: United States Department of Agriculture/Agricultural Research Service, Children's Nutrition Research Center, 1100 Bates Street, Houston, Texas 77030, USA. sabrams@bcm.edu
authors.forename: Steven A
authors.initials: SA
authors.lastname: Abrams
authors.forename: Ian J
authors.initials: IJ
authors.lastname: Griffin
authors.forename: Keli M
authors.initials: KM
authors.lastname: Hawthorne
authors.forename: Sheila K
authors.initials: SK
authors.lastname: Gunn
authors.forename: Caren M
authors.initials: CM
authors.lastname: Gundberg
authors.forename: Thomas O
authors.initials: TO
authors.lastname: Carpenter
mesh_terms: D015652:25-Hydroxyvitamin D 2 / Q000378:metabolism; D000293:Adolescent; D015519:Bone Density; D002118:Calcium / Q000378:metabolism*; D002648:Child; D004032:Diet; D019587:Dietary Supplements; D023381:Endpoint Determination; D005260:Female; D005838:Genotype; D006801:Humans; D008297:Male; D015675:Osteocalcin / Q000097:blood; D010281:Parathyroid Hormone / Q000097:blood*; D011627:Puberty / Q000502:physiology; D014807:Vitamin D / Q000097:blood*
chemical_list: D010281:Parathyroid Hormone; D015675:Osteocalcin; D014807:Vitamin D; D015652:25-Hydroxyvitamin D 2; D002118:Calcium