title: A comprehensive meta-analysis on dietary flavonoid and lignan intake and cancer risk: Level of evidence and limitations.
abstract: To summarize available evidence on the association between dietary flavonoid as well as lignan intake and cancer risk in observational studies.
  
  
  
  A systematic search on electronic databases of all English language case-control and prospective studies published up to June 2016 was performed. Risk ratios (RRs) and 95% confidence intervals were calculated by random-effects model separately by study design. Heterogeneity and publication bias were tested. Out of the 143 studies included, meta-analyses of prospective studies showed isoflavones significantly associated with decreased risk of lung and stomach cancers and nearly significant breast and colorectal cancers; total flavonoids showed nonsignificant decreased risk of breast cancer. Meta-analyses of case-control studies showed: total and/or individual classes of flavonoids associated with upper aero-digestive tract, colorectal, breast, and lung cancers; isoflavones with ovarian, breast, and colorectal cancers, endometrial and lung cancers.
  
  
  
  Most evidence reported in previous meta-analyses was driven by case-control studies. Overall results may be promising but are inconclusive. Further prospective cohorts assessing dietary polyphenol exposure and studies using other methods to evaluate exposure (i.e. markers of consumption, metabolism, excretion) are needed to confirm and determine consumption levels required to achieve health benefits.
authors.affiliation: Integrated Cancer Registry of Catania-Messina-Siracusa-Enna, Azienda Ospedaliero-Universitaria Policlinico-Vittorio Emanuele, Catania, Italy.|NNEdPro Global Centre for Nutrition and Health, St John's Innovation Centre, Cambridge, UK.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Grosso
authors.affiliation: Integrated Cancer Registry of Catania-Messina-Siracusa-Enna, Azienda Ospedaliero-Universitaria Policlinico-Vittorio Emanuele, Catania, Italy.
authors.forename: Justyna
authors.initials: J
authors.lastname: Godos
authors.affiliation: Biomedical Research Center Network on Obesity and Nutrition (CIBERobn) Physiopathology of Obesity and Nutrition, Institute of Health Carlos III, Madrid, Spain.|Nutrition and Food Science Department-XaRTA, INSA, University of Barcelona, Barcelona, Spain.
authors.forename: Rosa
authors.initials: R
authors.lastname: Lamuela-Raventos
authors.affiliation: NNEdPro Global Centre for Nutrition and Health, St John's Innovation Centre, Cambridge, UK.|Medical Research Council (MRC) Human Nutrition Research Unit, Cambridge, UK.
authors.forename: Sumantra
authors.initials: S
authors.lastname: Ray
authors.affiliation: Department of Epidemiology and Population Studies, Jagiellonian University Medical College, Krakow, Poland.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Micek
authors.affiliation: Department of Epidemiology and Population Studies, Jagiellonian University Medical College, Krakow, Poland.
authors.forename: Andrzej
authors.initials: A
authors.lastname: Pajak
authors.affiliation: Integrated Cancer Registry of Catania-Messina-Siracusa-Enna, Azienda Ospedaliero-Universitaria Policlinico-Vittorio Emanuele, Catania, Italy.
authors.forename: Salvatore
authors.initials: S
authors.lastname: Sciacca
authors.affiliation: Department of Medical and Oral Sciences and Biotechnologies, University of Chieti, Chieti, Italy.
authors.forename: Nicolantonio
authors.initials: N
authors.lastname: D'Orazio
authors.affiliation: NNEdPro Global Centre for Nutrition and Health, St John's Innovation Centre, Cambridge, UK.|Department of Food Science, University of Parma, Parma, Italy.
authors.forename: Daniele
authors.initials: D
authors.lastname: Del Rio
authors.affiliation: Department of Biomedical and Biotechnological Sciences, University of Catania, Catania, Italy.
authors.forename: Fabio
authors.initials: F
authors.lastname: Galvano
mesh_terms: D001943:Breast Neoplasms; D016022:Case-Control Studies; D015179:Colorectal Neoplasms; D004032:Diet; D005260:Female; D005419:Flavonoids / Q000008:administration & dosage*; D006801:Humans; D017705:Lignans / Q000008:administration & dosage*; D016017:Odds Ratio; D059808:Polyphenols / Q000008:administration & dosage*; D011446:Prospective Studies; D012307:Risk Factors
chemical_list: D005419:Flavonoids; D017705:Lignans; D059808:Polyphenols
keywords: Cancer; Dietary polyphenols; Flavonoids; Lignans; Meta-analysis; Observational studies