title: Blood concentrations of carotenoids and retinol and lung cancer risk: an update of the WCRF-AICR systematic review of published prospective studies.
abstract: Carotenoids and retinol are considered biomarkers of fruits and vegetables intake, and are of much interest because of their anti-inflammatory and antioxidant properties; however, there is inconsistent evidence regarding their protective effects against lung cancer. We conducted a meta-analysis of prospective studies of blood concentrations of carotenoids and retinol, and lung cancer risk. We identified relevant prospective studies published up to December 2014 by searching the PubMed and several other databases. We calculated summary estimates of lung cancer risk for the highest compared with lowest carotenoid and retinol concentrations and dose-response meta-analyses using random effects models. We used fractional polynomial models to assess potential nonlinear relationships. Seventeen prospective studies (18 publications) including 3603 cases and 458,434 participants were included in the meta-analysis. Blood concentrations of α-carotene, β-carotene, total carotenoids, and retinol were significantly inversely associated with lung cancer risk or mortality. The summary relative risk were 0.66 (95% confidence interval [CI]: 0.55-0.80) per 5 μg/100 mL of α-carotene (studies [n] = 5), 0.84 (95% CI: 0.76-0.94) per 20 μg/100 mL of β-carotene (n = 9), 0.66 (95% CI: 0.54-0.81) per 100 μg/100 mL of total carotenoids (n = 4), and 0.81 (95% CI: 0.73-0.90) per 70 μg/100 mL of retinol (n = 8). In stratified analysis by sex, the significant inverse associations for β-carotene and retinol were observed only in men and not in women. Nonlinear associations were observed for β-carotene, β-cryptoxanthin, and lycopene, with stronger associations observed at lower concentrations. There were not enough data to conduct stratified analyses by smoking. In conclusion, higher blood concentrations of several carotenoids and retinol are associated with reduced lung cancer risk. Further studies in never and former smokers are needed to rule out confounding by smoking.
authors.affiliation: Department of Epidemiology and Biostatistics, Imperial College, London, United Kingdom.
authors.forename: Leila
authors.initials: L
authors.lastname: Abar
authors.affiliation: Department of Epidemiology and Biostatistics, Imperial College, London, United Kingdom.
authors.forename: Ana Rita
authors.initials: AR
authors.lastname: Vieira
authors.affiliation: Department of Epidemiology and Biostatistics, Imperial College, London, United Kingdom.|Department of Public Health and General Practice, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: Dagfinn
authors.initials: D
authors.lastname: Aune
authors.affiliation: Department of Epidemiology and Biostatistics, Imperial College, London, United Kingdom.
authors.forename: Christophe
authors.initials: C
authors.lastname: Stevens
authors.affiliation: Department of Epidemiology and Biostatistics, Imperial College, London, United Kingdom.
authors.forename: Snieguole
authors.initials: S
authors.lastname: Vingeliene
authors.affiliation: Department of Epidemiology and Biostatistics, Imperial College, London, United Kingdom.
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Navarro Rosenblatt
authors.affiliation: Department of Epidemiology and Biostatistics, Imperial College, London, United Kingdom.
authors.forename: Doris
authors.initials: D
authors.lastname: Chan
authors.affiliation: Biostatistics Unit, Centre for Epidemiology and Biostatistics, University of Leeds, Leeds, United Kingdom.
authors.forename: Darren C
authors.initials: DC
authors.lastname: Greenwood
authors.affiliation: Department of Epidemiology and Biostatistics, Imperial College, London, United Kingdom.
authors.forename: Teresa
authors.initials: T
authors.lastname: Norat
mesh_terms: D015415:Biomarkers; D002338:Carotenoids / Q000097:blood*; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000097:blood* / Q000453:epidemiology*; D008297:Male; D019572:Retinal Neoplasms / Q000097:blood* / Q000453:epidemiology*; D012306:Risk
chemical_list: D015415:Biomarkers; D002338:Carotenoids
keywords: Carotenoids; continuous update project; lung cancer; meta-analysis; retinol