title: Plasma retinol-binding protein is not a marker of insulin resistance in overweight subjects: a three year longitudinal study.
abstract: OBJECTIVE
  This longitudinal study investigated whether or not plasma retinol-binding protein (RBP), recently referred to as RBP4, was a marker of insulin resistance in overweight subjects.
  
  
  METHODS
  We measured anthropometric markers as well as RBP, fasting glucose and insulin in 206 overweight subjects and repeated these measurements 36 months later. Subjects were grouped according to fasting plasma glucose concentration at baseline and 36 months.
  
  
  RESULTS
  Subjects (n=51) with a normal basal fasting glucose (<5.6 mmol/L) who developed impaired fasting glucose (IFG) 3 years later (>or=5.6 mmol/L) showed a highly significant increase in both fasting insulin and insulin resistance, but importantly no change in plasma RBP. This group had a significant increase in body mass index (BMI). Subjects (n=101) with a normal fasting glucose at both baseline (<5.6 mmol/L) and 36 months showed no significant change in fasting insulin, insulin resistance, RBP or BMI. The remaining subjects had impaired basal fasting glucose and were not analysed on a group-wise basis. Overall, RBP correlated significantly, but inversely, with anthropometric measures, but not with fasting glucose, insulin or insulin resistance.
  
  
  CONCLUSIONS
  This is the first report of a long-term longitudinal study on RBP and the major finding is that subjects who developed insulin resistance showed no change in plasma RBP. On the basis of our results we consider that RBP cannot be construed as a marker of insulin resistance in overweight humans.
authors.affiliation: Steroid and Immunobiochemistry Laboratory, Canterbury Health Laboratories, P.O. Box 151, Christchurch, New Zealand. john.lewis@cdhb.govt.nz
authors.forename: John G
authors.initials: JG
authors.lastname: Lewis
authors.forename: Brett I
authors.initials: BI
authors.lastname: Shand
authors.forename: Chris M
authors.initials: CM
authors.lastname: Frampton
authors.forename: Peter A
authors.initials: PA
authors.lastname: Elder
authors.forename: Russell S
authors.initials: RS
authors.lastname: Scott
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood*; D001786:Blood Glucose / Q000378:metabolism; D005260:Female; D006801:Humans; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance / Q000502:physiology*; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D050177:Overweight / Q000097:blood*; D054839:Retinol-Binding Proteins, Plasma / Q000378:metabolism*
chemical_list: D015415:Biomarkers; D001786:Blood Glucose; D007328:Insulin; C101326:RBP4 protein, human; D054839:Retinol-Binding Proteins, Plasma