title: Plasma vitamin D metabolites and risk of colorectal cancer in women.
abstract: OBJECTIVE
  Experimental evidence suggests that 1,25-dihydroxyvitamin D and its precursor, 25-hydroxyvitamin D [25(OH)D], may aid in the prevention of colorectal cancer. We therefore examined risk in relation to plasma concentrations of these vitamin D metabolites.
  
  
  METHODS
  In a nested case-control study among women in the Nurses' Health Study, we identified 193 colorectal cancer cases, ages 46 to 78 years, diagnosed up to 11 years after blood collection. Two controls were matched per case on year of birth and month of blood draw. Odds ratios (OR) for risk of colorectal cancer were calculated using conditional logistic regression adjusted for body mass index, physical activity, smoking, family history, use of hormone replacement therapy, aspirin use, and dietary intakes.
  
  
  RESULTS
  We found a significant inverse linear association between plasma 25(OH)D and risk of colorectal cancer (P = 0.02). Among women in the highest quintile, the OR (95% confidence interval) was 0.53 (0.27-1.04). This inverse association remained strong when limited to women > or =60 years at blood collection (P = 0.006) but was not apparent among the younger women (P = 0.70). Benefit from higher 25(OH)D concentrations was observed for cancers at the distal colon and rectum (P = 0.02) but was not evident for those at the proximal colon (P = 0.81). In contrast to 25(OH)D, we did not observe an association between 1,25-dihydroxyvitamin D and colorectal cancer, although risk was elevated among the women in the highest quintile if they were also in the lower half of the 25(OH)D distribution (OR, 2.52; 95% confidence interval, 1.04-6.11).
  
  
  CONCLUSIONS
  From these results and supporting evidence from previous studies, we conclude that higher plasma levels of 25(OH)D are associated with a lower risk of colorectal cancer in older women, particularly for cancers at the distal colon and rectum.
authors.affiliation: Channing Laboratory, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA. diane.feskanich@channing.harvard.edu
authors.forename: Diane
authors.initials: D
authors.lastname: Feskanich
authors.forename: Jing
authors.initials: J
authors.lastname: Ma
authors.forename: Charles S
authors.initials: CS
authors.lastname: Fuchs
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Kirkner
authors.forename: Susan E
authors.initials: SE
authors.lastname: Hankinson
authors.forename: Bruce W
authors.initials: BW
authors.lastname: Hollis
authors.forename: Edward L
authors.initials: EL
authors.lastname: Giovannucci
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D015179:Colorectal Neoplasms / Q000097:blood / Q000453:epidemiology*; D005247:Feeding Behavior; D005260:Female; D006306:Health Surveys; D006801:Humans; D016015:Logistic Models; D008875:Middle Aged; D016017:Odds Ratio; D012016:Reference Values; D012306:Risk; D014481:United States; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood*
chemical_list: D014807:Vitamin D; C097949:1,25-dihydroxyvitamin D; C104450:25-hydroxyvitamin D