title: Relationship between serum parathyroid hormone levels, vitamin D sufficiency, and calcium intake.
abstract: BACKGROUND
  Adequate vitamin D status for optimum bone health has received increased recognition in recent years; however, the ideal intake is not known. Serum 25-hydroxyvitamin D is the generally accepted indicator of vitamin D status, but no universal reference level has been reached.
  
  
  OBJECTIVE
  To investigate the relative importance of high calcium intake and serum 25-hydroxyvitamin D for calcium homeostasis, as determined by serum intact parathyroid hormone (PTH).
  
  
  METHODS
  Cross-sectional study of 2310 healthy Icelandic adults who were divided equally into 3 age groups (30-45 years, 50-65 years, or 70-85 years) and recruited from February 2001 to January 2003. They were administered a semi-quantitative food frequency questionnaire, which assessed vitamin D and calcium intake. Participants were further divided into groups according to calcium intake (<800 mg/d, 800-1200 mg/d, and >1200 mg/d) and serum 25-hydroxyvitamin D level (<10 ng/mL, 10-18 ng/mL, and >18 ng/mL).
  
  
  METHODS
  Serum intact PTH as determined by calcium intake and vitamin D.
  
  
  RESULTS
  A total of 944 healthy participants completed all parts of the study. After adjusting for relevant factors, serum PTH was lowest in the group with a serum 25-hydroxyvitamin D level of more than 18 ng/mL but highest in the group with a serum 25-hydroxyvitamin D level of less than 10 ng/mL. At the low serum 25-hydroxyvitamin D level (<10 ng/mL), calcium intake of less than 800 mg/d vs more than 1200 mg/d was significantly associated with higher serum PTH (P = .04); and at a calcium intake of more than 1200 mg/d, there was a significant difference between the lowest and highest vitamin D groups (P = .04).
  
  
  CONCLUSIONS
  As long as vitamin D status is ensured, calcium intake levels of more than 800 mg/d may be unnecessary for maintaining calcium metabolism. Vitamin D supplements are necessary for adequate vitamin D status in northern climates.
authors.affiliation: Public Health Institute of Iceland.
authors.forename: Laufey
authors.initials: L
authors.lastname: Steingrimsdottir
authors.forename: Orvar
authors.initials: O
authors.lastname: Gunnarsson
authors.forename: Olafur S
authors.initials: OS
authors.lastname: Indridason
authors.forename: Leifur
authors.initials: L
authors.lastname: Franzson
authors.forename: Gunnar
authors.initials: G
authors.lastname: Sigurdsson
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002118:Calcium / Q000008:administration & dosage* / Q000378:metabolism*; D003430:Cross-Sectional Studies; D004034:Diet Surveys; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood*; D014807:Vitamin D / Q000008:administration & dosage* / Q000031:analogs & derivatives* / Q000097:blood / Q000378:metabolism*
chemical_list: D010281:Parathyroid Hormone; D014807:Vitamin D; C104450:25-hydroxyvitamin D; D002118:Calcium