title: Effect of smoking on the serum levels of 25-hydroxyvitamin D depends on the assay employed.
abstract: OBJECTIVE
  Because we found higher serum 25-hydroxyvitamin D (25(OH)D) levels among smokers than among non-smokers with analyses using an electrochemiluminescence immunoassay (ECLIA) from Roche, the purpose of the present study was to examine whether this difference between smokers and non-smokers was maintained using other serum 25(OH)D assays.
  
  
  METHODS
  A cross-sectional population-based study on 6932 participants from the Tromsø study, 1994-1995, and one validation study comparing six different serum 25(OH)D assays in 53 non-smokers and 54 smokers were performed.
  
  
  METHODS
  The association between smoking, season and serum 25(OH)D as measured by ECLIA (Roche) was assessed in the population-based study using general linear models with multivariate adjustments. In the validation study, serum levels of 25(OH)D were analysed with liquid chromatography coupled with mass spectrometry assay from two different laboratories, RIA (DiaSorin), HPLC, RIA (IDS) and ECLIA (Roche). T-tests and linear mixed model analyses were performed to compare the serum 25(OH)D levels in smokers and non-smokers within and between the methods.
  
  
  RESULTS
  In the population-based study, the serum levels of 25(OH)D using the ECLIA method were 51.9, 53.2 and 72.0 nmol/l in never, former and current smokers (P<0.01). In the validation study, the serum concentration of 25(OH)D was 10.3 nmol/l higher in smokers than in non-smokers (P<0.01) using the ECLIA (Roche), while non-significantly lower serum levels of 25(OH)D were found in smokers using the other five methods.
  
  
  CONCLUSIONS
  These two studies indicate that the ECLIA (Roche) overestimates serum 25(OH)D levels in smokers by unknown mechanisms. If confirmed, this might have clinical consequences, and the issue needs further exploration.
authors.affiliation: Medical Clinic, University Hospital of North Norway, Tromsø, Norway. guri.grimnes@unn.no
authors.forename: Guri
authors.initials: G
authors.lastname: Grimnes
authors.forename: Bjørg
authors.initials: B
authors.lastname: Almaas
authors.forename: Anne Elise
authors.initials: AE
authors.lastname: Eggen
authors.forename: Nina
authors.initials: N
authors.lastname: Emaus
authors.forename: Yngve
authors.initials: Y
authors.lastname: Figenschau
authors.forename: Laila Arnesdatter
authors.initials: LA
authors.lastname: Hopstock
authors.forename: Moira Strand
authors.initials: MS
authors.lastname: Hutchinson
authors.forename: Paal
authors.initials: P
authors.lastname: Methlie
authors.forename: Albena
authors.initials: A
authors.lastname: Mihailova
authors.forename: Monica
authors.initials: M
authors.lastname: Sneve
authors.forename: Peter
authors.initials: P
authors.lastname: Torjesen
authors.forename: Tom
authors.initials: T
authors.lastname: Wilsgaard
authors.forename: Rolf
authors.initials: R
authors.lastname: Jorde
mesh_terms: D000328:Adult; D000368:Aged; D002853:Chromatography, Liquid / Q000592:standards*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000592:standards*; D008297:Male; D013058:Mass Spectrometry / Q000592:standards*; D008875:Middle Aged; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity; D012907:Smoking / Q000097:blood*; D011795:Surveys and Questionnaires; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D