title: A prospective study of aspirin use and the risk for colorectal adenoma.
abstract: BACKGROUND
  Randomized, double-blind, placebo-controlled trials have established that regular aspirin use reduces the risk for recurrent colorectal adenoma. However, the effect of dose and duration of use, particularly in an average-risk population, is not well understood.
  
  
  OBJECTIVE
  To examine the influence of dose and duration of aspirin use in the primary prevention of colorectal adenoma.
  
  
  METHODS
  Prospective cohort study.
  
  
  METHODS
  Nurses' Health Study.
  
  
  METHODS
  27 077 women, 34 to 77 years of age, without a history of adenoma, cancer, inflammatory bowel disease, or familial polyposis, who underwent lower endoscopy between 1980 and 1998.
  
  
  METHODS
  1368 cases of confirmed distal colorectal adenoma were diagnosed between 1980 and 1998. Self-reported data on aspirin use were collected from biennial questionnaires.
  
  
  RESULTS
  After other risk factors for adenoma were adjusted, women who regularly used aspirin (> or =2 standard aspirin tablets/wk) had a multivariate relative risk for adenoma of 0.75 (95% CI, 0.66 to 0.84) compared with nonregular users. Compared with women who denied any aspirin use, the multivariate relative risks for adenoma were 0.80 (CI, 0.70 to 0.93) for women who used 0.5 to 1.5 standard tablets per week, 0.74 (CI, 0.62 to 0.88) for those who used 2 to 5 tablets per week, 0.72 (CI, 0.61 to 0.85) for those who used 6 to 14 tablets per week, and 0.49 (CI, 0.36 to 0.65) for those who used more than 14 tablets per week (P < 0.001 for trend). Similar dose-response relationships were found among regular short-term users (< or =5 years; P < 0.001) and long-term users (>5 years; P < 0.001). In contrast, after adjustments were made for dose, increasing duration of aspirin use did not confer greater risk reduction (P > 0.2).
  
  
  CONCLUSIONS
  Regular, short-term use of aspirin is inversely associated with risk for colorectal adenoma. However, the greatest protective effect is evident at substantially higher doses (>14 tablets/wk) than those recommended for the prevention of cardiovascular disease. Before aspirin can be recommended for chemoprevention in the general adult population, these results suggest the need for a more thorough evaluation of the risks and benefits of routine aspirin use at doses not previously considered.
authors.affiliation: Massachusetts General Hospital, Brigham and Women's Hospital, Dana-Farber Cancer Institute, Harvard Medical School, and Harvard School of Public Health, Boston, Massachusetts 02114, USA.
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Chan
authors.forename: Edward L
authors.initials: EL
authors.lastname: Giovannucci
authors.forename: Eva S
authors.initials: ES
authors.lastname: Schernhammer
authors.forename: Graham A
authors.initials: GA
authors.lastname: Colditz
authors.forename: David J
authors.initials: DJ
authors.lastname: Hunter
authors.forename: Walter C
authors.initials: WC
authors.lastname: Willett
authors.forename: Charles S
authors.initials: CS
authors.lastname: Fuchs
mesh_terms: D000236:Adenoma / Q000517:prevention & control*; D000328:Adult; D000368:Aged; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000008:administration & dosage*; D001241:Aspirin / Q000008:administration & dosage*; D015179:Colorectal Neoplasms / Q000517:prevention & control*; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D008875:Middle Aged; D011446:Prospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D011795:Surveys and Questionnaires
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D001241:Aspirin