Does night work increase the risk of breast cancer? A systematic review and meta-analysis of epidemiological studies

Cancer Epidemiol. 2013 Jun;37(3):197-206. doi: 10.1016/j.canep.2013.01.005. Epub 2013 Feb 9.


Objective: To conduct a systematic review, with meta-analysis, of studies assessing the association between night work and the risk of breast cancer, using available epidemiological evidence.

Method: Relevant studies were identified by searching several databases and the reference lists of retrieved articles. We combined the relative risks (RR) from individual studies using a random-effects model. Subgroup analysis was carried out as the data showed statistically significant heterogeneity.

Results: Thirteen studies consisting of eight case-control studies and five cohort studies were included in the analysis. In the combined analysis of all studies, night work was associated with an increased risk for breast cancer (RR = 1.20, 95%CI = 1.08-1.33). The higher-quality studies showed a similar finding with a pooled RR of 1.40 (95%CI = 1.13-1.73). Both case-control studies (RR = 1.32, 95%CI = 1.17-1.50) and cohort studies (RR=1.08, 95%CI = 0.97-1.21) showed a positive association between night work and the risk of breast cancer. No publication bias was found either from Begg's funnel plot (P = 0.086) or the Egger's test (P = 0.107). Additional well-conducted and large-scale epidemiological studies are needed.

Publication types

  • Meta-Analysis
  • Review
  • Systematic Review

MeSH terms

  • Breast Neoplasms / epidemiology*
  • Case-Control Studies
  • Circadian Rhythm
  • Cohort Studies
  • Female
  • Humans
  • Incidence
  • Risk Factors
  • Work Schedule Tolerance*