Dietary intake of ω-6 and ω-3 fatty acids and risk of colorectal cancer in a prospective cohort of U.S. men and women

Background: ω-6 and ω-3 polyunsaturatedfatty acids intakes may play opposing roles in inflammation-driven colorectal carcinogenesis. We examined the relationship of these polyunsaturatedfatty acids and the ratio of their intake with colorectal cancer risk in a large U.S. prospective cohort. Design: Participants in the Cancer Prevention Study-II Nutrition Cohort completeda detailedquestionnaire on diet, medical history, and lifestyle in 1999. Between 1999 and 2005, 869 incident colorectal cancer cases (452 men and417 women) were identifiedamong 99,080 participants (43,108 men and 55,972 women). Multivariate-adjusted rate ratios were calculated using Cox proportional hazards models. Results: The ratio of total ω-6 to total ω-3 intake was not associatedwith colorectal cancer risk in either sex. Contrary to our initial hypothesis, total ω-6 intake was inversely relatedto colorectal cancer risk in men [multivariate relative risk (95% confidence interval) for highest to lowest quartile, 0.81 (0.61-1.07); P _trend = 0.07],and α-linolenic acid, the primary contributor to total ω-3 intake, was associatedwith increasedrisk in women for quartiles 2 through 4 versus the lowest quartile [relative risk (95% confidence interval), 1.50 (1.12-2.01), 1.40 (1.04-1.87), and 1.38 (1.02-1.85), respectively; P _trend = 0.13]. In women, total ω-6 andmarine ω-3 intake appearedto be associatedwith higher andlower risk, respectively, but associations were attenuated with adjustment for other risk factors. Conclusions: The ratio of ω-6 to ω-3 intake was not relatedto colorectal cancer risk in this cohort, which may be due to unexpected findings for the individual components. Differential associations by sex warrant further investigation.