title: Abdominal adiposity is not a mediator of the protective effect of Mediterranean diet on colorectal cancer.
abstract: Adherence to the Mediterranean diet (MD) has a preventive effect on colorectal cancer (CRC). Several biological mechanisms have been hypothesized to explain this effect, but the involvement of clinical mediators has not been experimentally proven. We examined the role of abdominal adiposity (i.e., waist-to-hip ratio, WHR) as a potential mediator of the relationship between the MD and CRC in the Italian centres of the European Prospective Investigation into Cancer and Nutrition. We evaluated the effect of the Italian Mediterranean Index (IMI) on WHR and of WHR on CRC risk. We then estimated the natural indirect effect (NIE, mediated by WHR) and the pure direct effect (PDE, unmediated) of IMI on CRC risk using mediation analyses, considering age, sex, education, physical activity, smoking and EPIC centre as confounders. Increased IMI was associated with significantly decreased odds of high WHR (odds ratio [OR] for an IMI of 6-11 vs. 0-1: 0.88, 95% confidence interval [CI]: 0.81-0.97). There was a positive relationship between WHR and CRC (hazard ratio [HR] for high vs. low WHR: 1.34, 95%CI: 1.09-1.66). The total effect of IMI was protective on CRC risk and was mainly explained by the PDE (HR for an IMI of 6-11 vs. 0-1: 0.51, 95%CI: 0.31-0.83), whereas the NIE was 1.00 (95%CI: 0.94-1.10). In this Mediterranean cohort, the protective effect of the MD on the development of CRC was not mediated by abdominal adiposity. Since this is the first study to investigate the mediating effect of abdominal obesity, other studies are needed to replicate this result.
authors.affiliation: Unit of Cancer Epidemiology, Department of Medical Sciences, University of Turin and Città della Salute e della Scienza University-Hospital Center for Cancer Prevention (CPO), Turin, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Fasanelli
authors.affiliation: Unit of Cancer Epidemiology, Department of Medical Sciences, University of Turin and Città della Salute e della Scienza University-Hospital Center for Cancer Prevention (CPO), Turin, Italy.
authors.forename: Daniela
authors.initials: D
authors.lastname: Zugna
authors.affiliation: Department of Mathematics, University of Turin, Turin, Italy.
authors.forename: Maria Teresa
authors.initials: MT
authors.lastname: Giraudo
authors.affiliation: Epidemiology and Prevention Unit, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: Vittorio
authors.identifier: 0000-0003-0122-8624
authors.initials: V
authors.lastname: Krogh
authors.affiliation: Epidemiology and Prevention Unit, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: Sara
authors.initials: S
authors.lastname: Grioni
authors.affiliation: Department of Clinical Medicine and Surgery, Federico II University, Naples, Italy.
authors.forename: Salvatore
authors.initials: S
authors.lastname: Panico
authors.affiliation: Department of Clinical Medicine and Surgery, Federico II University, Naples, Italy.
authors.forename: Amalia
authors.initials: A
authors.lastname: Mattiello
authors.affiliation: Cancer Risk Factors and Lifestyle Epidemiology Unit Cancer Research and Prevention Institute - ISPO, Florence, Italy.
authors.forename: Giovanna
authors.initials: G
authors.lastname: Masala
authors.affiliation: Cancer Risk Factors and Lifestyle Epidemiology Unit Cancer Research and Prevention Institute - ISPO, Florence, Italy.
authors.forename: Saverio
authors.initials: S
authors.lastname: Caini
authors.affiliation: Cancer Registry, Department of Prevention, ASP, Ragusa, Italy.
authors.forename: Rosario
authors.initials: R
authors.lastname: Tumino
authors.affiliation: Cancer Registry, Department of Prevention, ASP, Ragusa, Italy.
authors.forename: Graziella
authors.initials: G
authors.lastname: Frasca
authors.affiliation: Unit of Epidemiology, Regional Health Service, Grugliasco, Turin, Italy.|Department of Clinical and Biological Sciences, University of Turin, Orbassano (Torino), Italy.
authors.forename: Veronica
authors.initials: V
authors.lastname: Sciannameo
authors.affiliation: Unit of Cancer Epidemiology, Department of Medical Sciences, University of Turin and Città della Salute e della Scienza University-Hospital Center for Cancer Prevention (CPO), Turin, Italy.|Unit of Epidemiology, Regional Health Service, Grugliasco, Turin, Italy.
authors.forename: Fulvio
authors.initials: F
authors.lastname: Ricceri
authors.affiliation: Unit of Cancer Epidemiology, Department of Medical Sciences, University of Turin and Città della Salute e della Scienza University-Hospital Center for Cancer Prevention (CPO), Turin, Italy.
authors.forename: Carlotta
authors.identifier: 0000-0002-8008-5096
authors.initials: C
authors.lastname: Sacerdote
mesh_terms: D050154:Adiposity; D015992:Body Mass Index; D015179:Colorectal Neoplasms / Q000453:epidemiology / Q000517:prevention & control*; D038441:Diet, Mediterranean; D015444:Exercise; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007558:Italy / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D009752:Nutritional Status; D056128:Obesity, Abdominal; D011379:Prognosis; D011446:Prospective Studies; D012307:Risk Factors; D055105:Waist Circumference; D049629:Waist-Hip Ratio; D044465:White People