title: Obese young adults exhibit lower total and lower free serum 25-hydroxycholecalciferol in a randomized vitamin D intervention.
abstract: Although obesity is a risk factor for vitamin D insufficiency, its impact on vitamin D-binding protein (DBP) concentration, and thereby possibly also on free 25OHD, is less well known. Our aim was to compare total and free serum 25OHD, and DBP concentrations between obese and normal-weight young adults at baseline and their responses to cholecalciferol supplementation.
  
  
  
  A 12-week randomized, double-blinded clinical trial.
  
  
  
  Obese subjects N = 18 (BMI = 38, 67% men) with severe childhood-onset obesity and 24 normal-weight subjects (BMI = 23, 46% men), age between 15 and 25 years, were randomized into two groups to receive either placebo or cholecalciferol 50 μg (2000 IU) daily.
  
  
  
  At baseline, 6-week and 12-week blood samples and anthropometric measurements were collected; baseline body composition was assessed by dual-energy X-ray absorptiometry.
  
  
  
  At baseline, obese subjects had, compared with normal-weight, lower total and free serum 25OHD (49 vs 62 nmol/l, P = 0·041; 2·8 vs 4·7 pg/ml, P = 0·001), without differences in DBP concentrations (309 vs 346 μg/ml, P = 0·212). Cholecalciferol 50 μg per day increased both total and free 25OHD (ancova P < 0·001 and P = 0·021). The response of total 25OHD to supplementation was inferior in the obese compared with normal-weight subjects (P = 0·027). On the contrary, the change in free 25OHD concentration was similar in groups (P = 0·487).
  
  
  
  Obese young adults exhibit lower total and free 25OHD concentration, which is not directly explained by differences in DBP status. The response of free 25OHD to supplementation did not differ between obese and normal-weight subjects.
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.affiliation: Folkhälsan Research Centre, Helsinki, Finland.
authors.forename: Minna
authors.initials: M
authors.lastname: Pekkinen
authors.affiliation: Department of Cell Biology and Anatomy, Institute of Biomedicine, University of Turku, Turku, Finland.
authors.forename: Kaisa K
authors.initials: KK
authors.lastname: Ivaska
authors.affiliation: Children's Hospital, University of Helsinki and Helsinki University Hospital, Helsinki, Finland.
authors.forename: Sture
authors.initials: S
authors.lastname: Andersson
authors.affiliation: Children's Hospital, University of Helsinki and Helsinki University Hospital, Helsinki, Finland.|Folkhälsan Research Centre, Helsinki, Finland.|Department of Molecular Medicine and Surgery, and Center for Molecular Medicine, Karolinska Institutet, Stockholm, Sweden.|Department of Clinical Genetics, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: Outi
authors.initials: O
authors.lastname: Mäkitie
authors.affiliation: Children's Hospital, University of Helsinki and Helsinki University Hospital, Helsinki, Finland.|Folkhälsan Research Centre, Helsinki, Finland.
authors.forename: Heli
authors.initials: H
authors.lastname: Viljakainen
mesh_terms: D000293:Adolescent; D002112:Calcifediol / Q000097:blood; D002762:Cholecalciferol / Q000627:therapeutic use*; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008297:Male; D063766:Pediatric Obesity / Q000097:blood / Q000188:drug therapy*; D016896:Treatment Outcome; D014809:Vitamin D-Binding Protein / Q000097:blood; D055815:Young Adult
chemical_list: D014809:Vitamin D-Binding Protein; D002762:Cholecalciferol; D002112:Calcifediol