title: Associations between dietary fiber and colorectal polyp risk differ by polyp type and smoking status.
abstract: The association of dietary fiber intake with colorectal cancer risk is established. However, the association may differ between cigarette smokers and nonsmokers. We evaluated this hypothesis in a large colonoscopy-based case-control study. Dietary fiber intakes were estimated by self-administered food frequency questionnaire. Unconditional logistic regression analysis was used to estimate ORs and 95% CIs with adjustment for potential confounders. Analysis also was stratified by cigarette smoking and sex. High dietary fiber intake was associated with reduced risk of colorectal polyps (P-trend = 0.003). This association was found to be stronger among cigarette smokers (P-trend = 0.006) than nonsmokers (P-trend = 0.21), although the test for multiplicative interaction was not statistically significant (P = 0.11). This pattern of association was more evident for high-risk adenomatous polyps (ADs), defined as advanced or multiple ADs (P-interaction smoking and dietary fiber intake = 0.09). Among cigarette smokers who smoked ≥23 y, a 38% reduced risk of high-risk ADs was found to be associated with high intake of dietary fiber compared with those in the lowest quartile fiber intake group (P-trend = 0.004). No inverse association with dietary fiber intake was observed for low-risk ADs, defined as single nonadvanced ADs. Cigarette smoking may modify the association of dietary fiber intake with the risk of colorectal polyps, especially high-risk ADs, a well-established precursor of colorectal cancer.
authors.affiliation: Division of Epidemiology, Department of Medicine, Vanderbilt Epidemiology Center.
authors.forename: Zhenming
authors.initials: Z
authors.lastname: Fu
authors.forename: Martha J
authors.initials: MJ
authors.lastname: Shrubsole
authors.forename: Walter E
authors.initials: WE
authors.lastname: Smalley
authors.forename: Reid M
authors.initials: RM
authors.lastname: Ness
authors.forename: Wei
authors.initials: W
authors.lastname: Zheng
mesh_terms: D018256:Adenomatous Polyps / Q000453:epidemiology / Q000473:pathology; D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D003111:Colonic Polyps / Q000453:epidemiology* / Q000473:pathology; D003113:Colonoscopy; D015179:Colorectal Neoplasms / Q000453:epidemiology* / Q000473:pathology; D004043:Dietary Fiber / Q000008:administration & dosage*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011230:Precancerous Conditions / Q000453:epidemiology / Q000473:pathology; D012307:Risk Factors; D040242:Risk Reduction Behavior; D012907:Smoking / Q000453:epidemiology*; D013714:Tennessee / Q000453:epidemiology