title: Age-, gender-, and weight-related effects on levels of 25-hydroxyvitamin D are not mediated by vitamin D binding protein.
abstract: OBJECTIVE
  25-hydroxyvitamin D (25OHD) levels are inversely related to body weight, and have been reported to decline with age and be lower in women than men. We hypothesized that these findings might be explained by effects of these variables on vitamin D binding protein (DBP) levels. We set out to determine the relationships between DBP and gender, 25OHD, body weight and body composition.
  
  
  METHODS
  Cross-sectional analysis.
  
  
  METHODS
  One hundred healthy, middle-aged and older, community-dwelling men and women.
  
  
  METHODS
  All participants were measured for 25OHD, DBP, body weight, bone mineral density and body composition.
  
  
  RESULTS
  Women had higher mean DBP levels than men but lower total 25OHD levels [DBP: women, mean (SD) 339 (36) mg/l, men 307 (71) mg/l, P = 0.005; 25OHD: women 67 (23) nmol/l, men 91 (39) nmol/l, P < 0.001]. In women, there were significant positive relationships between DBP and albumin (r = 0.33) and 25OHD (r = 0.34) whereas in men there were no significant relationships between DBP and any measured variables. There was no significant relationship between DBP and age, body weight, body mass index, fat mass or percentage fat in men or women.
  
  
  CONCLUSIONS
  We found no evidence to support the hypothesis that DBP levels are related to age, or adiposity. The changes in 25OHD levels with age, gender, or fat mass are not due to underlying relationships between DBP and these variables. This suggests that the relationships consistently observed between 25OHD and body composition and gender are of biological origin and not due to adaptation to changes in transport proteins.
authors.affiliation: Department of Medicine, University of Auckland, Auckland, New Zealand. m.bolland@auckland.ac.nz
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Bolland
authors.forename: Andrew B
authors.initials: AB
authors.lastname: Grey
authors.forename: Ruth W
authors.initials: RW
authors.lastname: Ames
authors.forename: Anne M
authors.initials: AM
authors.lastname: Horne
authors.forename: Barbara H
authors.initials: BH
authors.lastname: Mason
authors.forename: Diana J
authors.initials: DJ
authors.lastname: Wattie
authors.forename: Greg D
authors.initials: GD
authors.lastname: Gamble
authors.forename: Roger
authors.initials: R
authors.lastname: Bouillon
authors.forename: Ian R
authors.initials: IR
authors.lastname: Reid
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D001823:Body Composition; D001835:Body Weight; D015519:Bone Density; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D012737:Sex Factors; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014809:Vitamin D-Binding Protein / Q000097:blood*
chemical_list: D014809:Vitamin D-Binding Protein; D014807:Vitamin D; C104450:25-hydroxyvitamin D