title: Serum 25-hydroxyvitamin D concentration does not independently predict incident diabetes in older women.
abstract: OBJECTIVE
  To investigate whether 25-hydroxyvitamin D concentration was associated with incident diabetes in a large cohort of older women.
  
  
  METHODS
  Data were analysed from women included in the Study of Osteoporotic Fractures, a cohort of community-dwelling women aged ≥65 years at enrolment. Serum 25-hydroxyvitamin D concentration was assessed at the year 6 visit, as were BMI and other factors associated with vitamin D and/or diabetes. Diabetes status was determined at each subsequent visit by self-report and medication use. Only those without prevalent diabetes at the year 6 visit were included in the present analysis (N = 5463, mean age 76.5 years).
  
  
  RESULTS
  During a mean ±sd follow-up of 8.6 ± 4.4 years, incident diabetes was reported in 320 participants. The mean BMI was higher in those with a 25-hydroxyvitamin D concentration <20 ng/ml (<50 nmol/l) than in those with concentrations 20-30 or ≥30 ng/ml [50-74 or ≥75 nmol/l (P < 0.0001)]. A higher 25-hydroxyvitamin D concentration was associated with a 13% lower risk of incident diabetes after adjustment for age and clinic site [hazard ratio 0.87, 95% CI 0.76-0.99, per sd increase in 25-hydroxyvitamin D]; however, the addition of BMI to the model attenuated the estimated effect (hazard ratio 0.97, 95% CI 0.86-1.11). Adjustment for additional potential confounders yielded similar results.
  
  
  CONCLUSIONS
  Serum 25-hydroxyvitamin D does not independently predict incident diabetes in older women. Although those with higher 25-hydroxyvitamin D concentrations are less likely to develop diabetes, this is mainly explained by their lower BMI.
authors.affiliation: Department of Medicine, University of California, San Francisco, CA, USA; Endocrine Research Unit, Veterans Affairs Medical Center, San Francisco, CA, USA.
authors.forename: A L
authors.initials: AL
authors.lastname: Schafer
authors.forename: N
authors.initials: N
authors.lastname: Napoli
authors.forename: L
authors.initials: L
authors.lastname: Lui
authors.forename: A V
authors.initials: AV
authors.lastname: Schwartz
authors.forename: D M
authors.initials: DM
authors.lastname: Black
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000097:blood; D015992:Body Mass Index; D015331:Cohort Studies; D003924:Diabetes Mellitus, Type 2 / Q000097:blood* / Q000453:epidemiology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008137:Longitudinal Studies; D011237:Predictive Value of Tests; D012307:Risk Factors; D012737:Sex Factors; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood
chemical_list: D015415:Biomarkers; D014807:Vitamin D; C104450:25-hydroxyvitamin D