title: Night Shift Work and Breast Cancer Incidence: Three Prospective Studies and Meta-analysis of Published Studies.
abstract: It has been proposed that night shift work could increase breast cancer incidence. A 2007 World Health Organization review concluded, mainly from animal evidence, that shift work involving circadian disruption is probably carcinogenic to humans. We therefore aimed to generate prospective epidemiological evidence on night shift work and breast cancer incidence.
  
  
  
  Overall, 522 246 Million Women Study, 22 559 EPIC-Oxford, and 251 045 UK Biobank participants answered questions on shift work and were followed for incident cancer. Cox regression yielded multivariable-adjusted breast cancer incidence rate ratios (RRs) and 95% confidence intervals (CIs) for night shift work vs no night shift work, and likelihood ratio tests for interaction were used to assess heterogeneity. Our meta-analyses combined these and relative risks from the seven previously published prospective studies (1.4 million women in total), using inverse-variance weighted averages of the study-specific log RRs.
  
  
  
  In the Million Women Study, EPIC-Oxford, and UK Biobank, respectively, 673, 28, and 67 women who reported night shift work developed breast cancer, and the RRs for any vs no night shift work were 1.00 (95% CI = 0.92 to 1.08), 1.07 (95% CI = 0.71 to 1.62), and 0.78 (95% CI = 0.61 to 1.00). In the Million Women Study, the RR for 20 or more years of night shift work was 1.00 (95% CI = 0.81 to 1.23), with no statistically significant heterogeneity by sleep patterns or breast cancer risk factors. Our meta-analysis of all 10 prospective studies included 4660 breast cancers in women reporting night shift work; compared with other women, the combined relative risks were 0.99 (95% CI = 0.95 to 1.03) for any night shift work, 1.01 (95% CI = 0.93 to 1.10) for 20 or more years of night shift work, and 1.00 (95% CI = 0.87 to 1.14) for 30 or more years.
  
  
  
  The totality of the prospective evidence shows that night shift work, including long-term shift work, has little or no effect on breast cancer incidence.
authors.affiliation: Cancer Epidemiology Unit, Nuffield Department of Population Health, University of Oxford, Oxford, UK (RCT, AB, GKF, PNA, GKR, XSW, AWR, TG, JG, TJK, VB); Worldwide Epidemiology, GlaxoSmithKline R&D, Uxbridge, UK (AWR); Department of Oncoplastic Breast Surgery, Oxford University Hospitals NHS Trust, Oxford, UK (TG); Clinical Trial Service Unit and Epidemiological Studies Unit (CTSU), Nuffield Department of Population Health, University of Oxford, Oxford, UK (RP) ruth.travis@ceu.ox.ac.uk.
authors.forename: Ruth C
authors.initials: RC
authors.lastname: Travis
authors.affiliation: Cancer Epidemiology Unit, Nuffield Department of Population Health, University of Oxford, Oxford, UK (RCT, AB, GKF, PNA, GKR, XSW, AWR, TG, JG, TJK, VB); Worldwide Epidemiology, GlaxoSmithKline R&D, Uxbridge, UK (AWR); Department of Oncoplastic Breast Surgery, Oxford University Hospitals NHS Trust, Oxford, UK (TG); Clinical Trial Service Unit and Epidemiological Studies Unit (CTSU), Nuffield Department of Population Health, University of Oxford, Oxford, UK (RP).
authors.forename: Angela
authors.initials: A
authors.lastname: Balkwill
authors.affiliation: Cancer Epidemiology Unit, Nuffield Department of Population Health, University of Oxford, Oxford, UK (RCT, AB, GKF, PNA, GKR, XSW, AWR, TG, JG, TJK, VB); Worldwide Epidemiology, GlaxoSmithKline R&D, Uxbridge, UK (AWR); Department of Oncoplastic Breast Surgery, Oxford University Hospitals NHS Trust, Oxford, UK (TG); Clinical Trial Service Unit and Epidemiological Studies Unit (CTSU), Nuffield Department of Population Health, University of Oxford, Oxford, UK (RP).
authors.forename: Georgina K
authors.initials: GK
authors.lastname: Fensom
authors.affiliation: Cancer Epidemiology Unit, Nuffield Department of Population Health, University of Oxford, Oxford, UK (RCT, AB, GKF, PNA, GKR, XSW, AWR, TG, JG, TJK, VB); Worldwide Epidemiology, GlaxoSmithKline R&D, Uxbridge, UK (AWR); Department of Oncoplastic Breast Surgery, Oxford University Hospitals NHS Trust, Oxford, UK (TG); Clinical Trial Service Unit and Epidemiological Studies Unit (CTSU), Nuffield Department of Population Health, University of Oxford, Oxford, UK (RP).
authors.forename: Paul N
authors.initials: PN
authors.lastname: Appleby
authors.affiliation: Cancer Epidemiology Unit, Nuffield Department of Population Health, University of Oxford, Oxford, UK (RCT, AB, GKF, PNA, GKR, XSW, AWR, TG, JG, TJK, VB); Worldwide Epidemiology, GlaxoSmithKline R&D, Uxbridge, UK (AWR); Department of Oncoplastic Breast Surgery, Oxford University Hospitals NHS Trust, Oxford, UK (TG); Clinical Trial Service Unit and Epidemiological Studies Unit (CTSU), Nuffield Department of Population Health, University of Oxford, Oxford, UK (RP).
authors.forename: Gillian K
authors.initials: GK
authors.lastname: Reeves
authors.affiliation: Cancer Epidemiology Unit, Nuffield Department of Population Health, University of Oxford, Oxford, UK (RCT, AB, GKF, PNA, GKR, XSW, AWR, TG, JG, TJK, VB); Worldwide Epidemiology, GlaxoSmithKline R&D, Uxbridge, UK (AWR); Department of Oncoplastic Breast Surgery, Oxford University Hospitals NHS Trust, Oxford, UK (TG); Clinical Trial Service Unit and Epidemiological Studies Unit (CTSU), Nuffield Department of Population Health, University of Oxford, Oxford, UK (RP).
authors.forename: Xiao-Si
authors.initials: XS
authors.lastname: Wang
authors.affiliation: Cancer Epidemiology Unit, Nuffield Department of Population Health, University of Oxford, Oxford, UK (RCT, AB, GKF, PNA, GKR, XSW, AWR, TG, JG, TJK, VB); Worldwide Epidemiology, GlaxoSmithKline R&D, Uxbridge, UK (AWR); Department of Oncoplastic Breast Surgery, Oxford University Hospitals NHS Trust, Oxford, UK (TG); Clinical Trial Service Unit and Epidemiological Studies Unit (CTSU), Nuffield Department of Population Health, University of Oxford, Oxford, UK (RP).
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Roddam
authors.affiliation: Cancer Epidemiology Unit, Nuffield Department of Population Health, University of Oxford, Oxford, UK (RCT, AB, GKF, PNA, GKR, XSW, AWR, TG, JG, TJK, VB); Worldwide Epidemiology, GlaxoSmithKline R&D, Uxbridge, UK (AWR); Department of Oncoplastic Breast Surgery, Oxford University Hospitals NHS Trust, Oxford, UK (TG); Clinical Trial Service Unit and Epidemiological Studies Unit (CTSU), Nuffield Department of Population Health, University of Oxford, Oxford, UK (RP).
authors.forename: Toral
authors.initials: T
authors.lastname: Gathani
authors.affiliation: Cancer Epidemiology Unit, Nuffield Department of Population Health, University of Oxford, Oxford, UK (RCT, AB, GKF, PNA, GKR, XSW, AWR, TG, JG, TJK, VB); Worldwide Epidemiology, GlaxoSmithKline R&D, Uxbridge, UK (AWR); Department of Oncoplastic Breast Surgery, Oxford University Hospitals NHS Trust, Oxford, UK (TG); Clinical Trial Service Unit and Epidemiological Studies Unit (CTSU), Nuffield Department of Population Health, University of Oxford, Oxford, UK (RP).
authors.forename: Richard
authors.initials: R
authors.lastname: Peto
authors.affiliation: Cancer Epidemiology Unit, Nuffield Department of Population Health, University of Oxford, Oxford, UK (RCT, AB, GKF, PNA, GKR, XSW, AWR, TG, JG, TJK, VB); Worldwide Epidemiology, GlaxoSmithKline R&D, Uxbridge, UK (AWR); Department of Oncoplastic Breast Surgery, Oxford University Hospitals NHS Trust, Oxford, UK (TG); Clinical Trial Service Unit and Epidemiological Studies Unit (CTSU), Nuffield Department of Population Health, University of Oxford, Oxford, UK (RP).
authors.forename: Jane
authors.initials: J
authors.lastname: Green
authors.affiliation: Cancer Epidemiology Unit, Nuffield Department of Population Health, University of Oxford, Oxford, UK (RCT, AB, GKF, PNA, GKR, XSW, AWR, TG, JG, TJK, VB); Worldwide Epidemiology, GlaxoSmithKline R&D, Uxbridge, UK (AWR); Department of Oncoplastic Breast Surgery, Oxford University Hospitals NHS Trust, Oxford, UK (TG); Clinical Trial Service Unit and Epidemiological Studies Unit (CTSU), Nuffield Department of Population Health, University of Oxford, Oxford, UK (RP).
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Key
authors.affiliation: Cancer Epidemiology Unit, Nuffield Department of Population Health, University of Oxford, Oxford, UK (RCT, AB, GKF, PNA, GKR, XSW, AWR, TG, JG, TJK, VB); Worldwide Epidemiology, GlaxoSmithKline R&D, Uxbridge, UK (AWR); Department of Oncoplastic Breast Surgery, Oxford University Hospitals NHS Trust, Oxford, UK (TG); Clinical Trial Service Unit and Epidemiological Studies Unit (CTSU), Nuffield Department of Population Health, University of Oxford, Oxford, UK (RP).
authors.forename: Valerie
authors.initials: V
authors.lastname: Beral
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000453:epidemiology*; D002940:Circadian Rhythm; D005260:Female; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D010561:Personnel Staffing and Scheduling; D011446:Prospective Studies; D011795:Surveys and Questionnaires; D006113:United Kingdom / Q000453:epidemiology; D014940:Work Schedule Tolerance; D055815:Young Adult