title: Non-linear relationship between serum 25-hydroxyvitamin D concentration and subsequent hip fracture.
abstract: Serum 25-OH vitamin D levels were compared in 254 hip fracture subjects and 2,402 matched control subjects. There was a significant inverse association between 25-OH vitamin D and hip fracture only between 0 and 70 nmol/L.
  
  
  BACKGROUND
  Vitamin D is integral to bone metabolism, however the utility of serum 25-OH vitamin D as a risk marker for hip fractures is controversial.
  
  
  METHODS
  We conducted a case-control study of patients admitted to the hospitals with hip fractures in Calgary, Alberta, (catchment population 1.4 million) between January 1, 2007 and August 31, 2011. We searched the laboratory information system of Calgary Laboratory Services for serum 25-OH vitamin D levels within 6 months prior to admission on patients admitted to hospital with hip fractures. Cases were identified through the Calgary Laboratory Services laboratory information system and were matched to controls for age, sex, and month of testing. The hip fracture-25-OH vitamin D association was examined using multiple linear and spline regression.
  
  
  RESULTS
  Of 305 subjects initially identified with hip fractures, serum 25-OH vitamin D levels were available for 254 (83 %). These were matched to 2,402 control subjects. We observed a significant (p < 0.01) non-linear relationship such that 25-OH vitamin D was inversely associated with hip fracture only below 70 nmol/L (odds ratio = 0.81 per 10 nmol/L increase; 95 % CI 0.86-0.93).
  
  
  CONCLUSIONS
  The utility of 25-OH vitamin D level as a risk marker for hip fracture depends on the cut-off level used and was of potential use only for lower levels of 25-OH vitamin D.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Calgary, Calgary, Alberta, Canada.
authors.forename: L
authors.initials: L
authors.lastname: de Koning
authors.forename: D
authors.initials: D
authors.lastname: Henne
authors.forename: B R
authors.initials: BR
authors.lastname: Hemmelgarn
authors.forename: P
authors.initials: P
authors.lastname: Woods
authors.forename: C
authors.initials: C
authors.lastname: Naugler
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000097:blood; D016022:Case-Control Studies; D005260:Female; D006620:Hip Fractures / Q000097:blood* / Q000209:etiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D058866:Osteoporotic Fractures / Q000097:blood* / Q000209:etiology; D018570:Risk Assessment / Q000379:methods; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood / Q000150:complications
chemical_list: D015415:Biomarkers; D014807:Vitamin D; C104450:25-hydroxyvitamin D