title: Dietary compared with blood concentrations of carotenoids and breast cancer risk: a systematic review and meta-analysis of prospective studies.
abstract: BACKGROUND
  Measurement errors in the dietary assessment of fruit and vegetable intake may attenuate associations with breast cancer risk and might explain the weak associations observed in epidemiologic studies. Carotenoid concentrations in blood are biomarkers of fruit and vegetable intake; however, no systematic assessment has compared dietary intake with blood concentrations of carotenoids and breast cancer risk.
  
  
  OBJECTIVE
  We conducted a systematic review and meta-analysis of prospective studies of dietary intake and blood concentrations of carotenoids and breast cancer risk.
  
  
  METHODS
  We searched PubMed and several other databases for relevant studies up to 31 August 2011. Random-effects models were used to estimate summary estimates.
  
  
  RESULTS
  Of the 6 dietary carotenoids assessed, only intake of β-carotene was significantly associated with a reduced breast cancer risk (summary RR: 0.95; 95% CI: 0.91, 0.99; I(2): 0%) per 5000 μg/d (n = 10). In contrast, the summary RR for blood concentrations of carotenoids was 0.78 (95% CI: 0.61, 0.99; I(2): 53%) per 100 μg total carotenoids/dL (n = 7), 0.74 (95% CI: 0.57, 0.97; I(2): 43%) per 50 μg β-carotene/dL (n = 13), 0.82 (95% CI: 0.73, 0.92, I(2): 3%) per 10 μg α-carotene/dL (n = 12), and 0.68 (95% CI: 0.52, 0.89; I(2): 0%) per 25 μg lutein/dL (n = 6).
  
  
  CONCLUSIONS
  Blood concentrations of carotenoids are more strongly associated with reduced breast cancer risk than are carotenoids assessed by dietary questionnaires. Our results suggest that the use of certain biomarkers may clarify inconsistent and weak results between dietary intake and breast cancer risk.
authors: Department of Epidemiology and Biostatistics, School of Public Health, Imperial College, London, United Kingdom. d.aune@imperial.ac.uk
authors: Dagfinn
authors: D
authors: Aune
authors: Doris S M
authors: DS
authors: Chan
authors: Ana Rita
authors: AR
authors: Vieira
authors: Deborah A
authors: DA
authors: Navarro Rosenblatt
authors: Rui
authors: R
authors: Vieira
authors: Darren C
authors: DC
authors: Greenwood
authors: Teresa
authors: T
authors: Norat
mesh_terms: D015415:Biomarkers / Q000097:blood; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000209:etiology; D002338:Carotenoids / Q000008:administration & dosage* / Q000097:blood*; D065366:Cryptoxanthins; D004032:Diet; D019587:Dietary Supplements; D005260:Female; D005638:Fruit; D006801:Humans; D014975:Lutein / Q000008:administration & dosage / Q000097:blood; D000077276:Lycopene; D012307:Risk Factors; D014675:Vegetables; D024341:Xanthophylls / Q000008:administration & dosage / Q000097:blood; D065146:Zeaxanthins; D019207:beta Carotene / Q000008:administration & dosage* / Q000097:blood*
chemical_list: D015415:Biomarkers; D065366:Cryptoxanthins; D024341:Xanthophylls; D065146:Zeaxanthins; D019207:beta Carotene; D002338:Carotenoids; C041635:alpha-carotene; D000077276:Lycopene; D014975:Lutein