title: Influence of vitamin D binding protein on the association between circulating vitamin D and risk of bladder cancer.
abstract: BACKGROUND
  There is little research investigating the role of vitamin D binding protein (DBP) in the association between 25-hydroxyvitamin D (25(OH)D) and disease risk.
  
  
  METHODS
  Within the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) Study, 250 bladder cancer cases were randomly sampled and matched 1:1 to controls on age and date of blood collection. Odds ratios (OR) and 95% confidence intervals (CI) of bladder cancer were estimated by quartiles of DBP (measured by ELISA), 25(OH)D and the molar ratio of 25(OH)D:DBP, a proxy for free circulating 25(OH)D. Analyses were also conducted stratifying 25(OH)D by DBP (median split) and vice versa.
  
  
  RESULTS
  We found no direct association between circulating DBP levels and bladder cancer risk (P-trend=0.83). The inverse association between 25(OH)D and bladder cancer risk was unchanged after adjustment for DBP (Q4 vs Q1 OR=0.61, 95% CI=0.36-1.05; P-trend=0.04), and was stronger among men with lower DBP (low DBP: 25(OH)D Q4 vs Q1 OR=0.47, 95% CI=0.23-1.00; high DBP: 25(OH)D Q4 vs Q1 OR=0.83, 95% CI=0.40-1.75; P for interaction=0.11).
  
  
  CONCLUSIONS
  Our findings provide additional support for an aetiologic role for vitamin D in bladder cancer and suggest that free, rather than total, circulating vitamin D may be a more relevant exposure when examining bladder and, perhaps, other cancers.
authors.affiliation: Nutritional Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, NIH, Department of Health and Human Services, 6120 Executive Boulevard, Suite 320, Rockville, MD, USA. mondulam@mail.nih.gov
authors.forename: A M
authors.initials: AM
authors.lastname: Mondul
authors.forename: S J
authors.initials: SJ
authors.lastname: Weinstein
authors.forename: J
authors.initials: J
authors.lastname: Virtamo
authors.forename: D
authors.initials: D
authors.lastname: Albanes
mesh_terms: D016588:Anticarcinogenic Agents / Q000627:therapeutic use; D016022:Case-Control Studies; D004311:Double-Blind Method; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012307:Risk Factors; D001749:Urinary Bladder Neoplasms / Q000097:blood* / Q000517:prevention & control; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014809:Vitamin D-Binding Protein / Q000097:blood*; D024502:alpha-Tocopherol / Q000627:therapeutic use; D019207:beta Carotene / Q000627:therapeutic use
chemical_list: D016588:Anticarcinogenic Agents; D014809:Vitamin D-Binding Protein; D019207:beta Carotene; D014807:Vitamin D; C104450:25-hydroxyvitamin D; D024502:alpha-Tocopherol