title: Dietary supplement use and colorectal cancer risk: a systematic review and meta-analyses of prospective cohort studies.
abstract: Use of dietary supplements is rising in countries where colorectal cancer is prevalent. We conducted a systematic literature review and meta-analyses of prospective cohort studies on dietary supplement use and colorectal cancer risk. We identified relevant studies in Medline, Embase and Cochrane up to January 2013. Original and peer-reviewed papers on dietary supplement use and colorectal cancer, colon cancer, or rectal cancer incidence were included. "Use-no use"(U-NU), "highest-lowest"(H-L) and "dose-response"(DR) meta-analyses were performed. Random-effects models were used to estimate summary estimates. In total, 24 papers were included in the meta-analyses. We observed inverse associations for colorectal cancer risk and multivitamin (U-NU: RR = 0.92; 95% CI: 0.87,0.97) and calcium supplements (U-NU: RR = 0.86; 95% CI: 0.79,0.95; H-L: RR = 0.80; 95% CI: 0.70,0.92; DR: for an increase of 100 mg/day, RR = 0.96; 95% CI: 0.94,0.99). Inconsistent associations were found for colon cancer risk and supplemental vitamin A and vitamin C, and for colorectal cancer risk and supplemental vitamin D, vitamin E, garlic and folic acid. Meta-analyses of observational studies suggest a beneficial role for multivitamins and calcium supplements on colorectal cancer risk, while the association with other supplements and colorectal cancer risk is inconsistent. Residual confounding of lifestyle factors might be present. Before recommendations can be made, an extensive assessment of dietary supplement use and a better understanding of underlying mechanisms is needed.
authors.affiliation: Division of Human Nutrition, Wageningen University, Wageningen, The Netherlands.
authors.forename: Renate C
authors.initials: RC
authors.lastname: Heine-Bröring
authors.forename: Renate M
authors.initials: RM
authors.lastname: Winkels
authors.forename: Jacoba M S
authors.initials: JM
authors.lastname: Renkema
authors.forename: Lea
authors.initials: L
authors.lastname: Kragt
authors.forename: Anne-Claire B
authors.initials: AC
authors.lastname: van Orten-Luiten
authors.forename: Ettje F
authors.initials: EF
authors.lastname: Tigchelaar
authors.forename: Doris S M
authors.initials: DS
authors.lastname: Chan
authors.forename: Teresa
authors.initials: T
authors.lastname: Norat
authors.forename: Ellen
authors.initials: E
authors.lastname: Kampman
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002136:Calcium, Dietary / Q000008:administration & dosage*; D015179:Colorectal Neoplasms / Q000453:epidemiology* / Q000517:prevention & control; D019992:Databases as Topic; D019587:Dietary Supplements; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012307:Risk Factors; D014815:Vitamins / Q000008:administration & dosage*; D055815:Young Adult
chemical_list: D002136:Calcium, Dietary; D014815:Vitamins
keywords: colorectal cancer; dietary supplements; epidemiology; meta-analysis; nutrition; review