title: Blood levels of long-chain polyunsaturated fatty acids, aspirin, and the risk of colorectal cancer.
abstract: BACKGROUND
  N-3 fatty acids may decrease risk of colorectal cancer by inhibiting the cyclooxygenase-2 enzyme and production of proinflammatory eicosanoids derived from arachidonic acid (20:4n-6). Aspirin also inhibits the cyclooxygenase-2 enzyme and may share with n-3 fatty acids a potential mechanism to decrease the risk of colorectal cancer.
  
  
  METHODS
  We conducted a nested case-control analysis using blood samples collected from the Physicians' Health Study participants in 1982 to 1984. N-3 and n-6 fatty acid levels were measured using gas-liquid chromatography for 178 men who developed colorectal cancer through December 31, 1995 and 282 age- and smoking-matched controls. We used conditional logistic regression to examine associations. All statistical tests were two-sided.
  
  
  RESULTS
  Total long-chain n-3 fatty acids were nonsignificantly inversely associated with colorectal cancer risk [relative risk (RR) for highest versus lowest quartile, 0.60; 95% confidence interval (95% CI), 0.32 to 1.11; P(trend) = 0.10], after adjustment for possible confounders. We observed potential interaction between randomized aspirin assignment and long-chain n-3 fatty acid levels (P(interaction) = 0.04). Among men not on aspirin, RRs (95% CI) for increasing quartiles of long-chain n-3 fatty acids were 1.00 (reference), 0.60 (0.28-1.28), 0.51 (0.22-1.17), and 0.34 (0.15-0.82), P(trend) = 0.006. For participants taking aspirin, there was no additional benefit of increasing n-3 fatty acid levels. The RR (95% CI) for the highest versus lowest quartile of n-6 fatty acids was 0.64 (0.35-1.17).
  
  
  CONCLUSIONS
  Blood levels of long-chain n-3 fatty acids were associated with decreased risk of colorectal cancer among men not using aspirin. N-6 fatty acids were nonsignificantly inversely associated with colorectal cancer risk.
authors.affiliation: Department of Nutrition, Harvard School of Public Health, Boston, MA, USA.
authors.forename: Megan N
authors.initials: MN
authors.lastname: Hall
authors.forename: Hannia
authors.initials: H
authors.lastname: Campos
authors.forename: Haojie
authors.initials: H
authors.lastname: Li
authors.forename: Howard D
authors.initials: HD
authors.lastname: Sesso
authors.forename: Meir J
authors.initials: MJ
authors.lastname: Stampfer
authors.forename: Walter C
authors.initials: WC
authors.lastname: Willett
authors.forename: Jing
authors.initials: J
authors.lastname: Ma
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000008:administration & dosage* / Q000494:pharmacology; D001241:Aspirin / Q000008:administration & dosage* / Q000494:pharmacology; D002318:Cardiovascular Diseases / Q000517:prevention & control; D016022:Case-Control Studies; D015179:Colorectal Neoplasms / Q000097:blood* / Q000517:prevention & control; D015525:Fatty Acids, Omega-3 / Q000097:blood*; D043371:Fatty Acids, Omega-6 / Q000097:blood*; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000517:prevention & control; D011446:Prospective Studies; D016032:Randomized Controlled Trials as Topic; D012306:Risk; D012307:Risk Factors; D011795:Surveys and Questionnaires
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D015525:Fatty Acids, Omega-3; D043371:Fatty Acids, Omega-6; D001241:Aspirin