Cancer Causes & Control

, Volume 26, Issue 1, pp 143–150 | Cite as

Shift work and breast cancer among women textile workers in Shanghai, China

  • Wenjin Li
  • Roberta M. Ray
  • David B. Thomas
  • Scott Davis
  • Michael Yost
  • Norman Breslow
  • Dao Li Gao
  • E. Dawn Fitzgibbons
  • Janice E. Camp
  • Eva Wong
  • Karen J. Wernli
  • Harvey Checkoway
Original paper

Abstract

Purpose

Although night-shift work has been associated with elevated risk of breast cancer in numerous epidemiologic studies, evidence is not consistent. We conducted a nested case–cohort study to investigate a possible association between shift work including a night shift and risk of breast cancer within a large cohort of women textile workers in Shanghai, China.

Methods

The study included 1,709 incident breast cancer cases and 4,780 non-cases. Data on historical shift work schedules were collected by categorized jobs from the factories, where the study subjects had worked, and then were linked to the complete work histories of each subject. No jobs in the factories involved exclusively night-shift work. Therefore, night shift was evaluated as part of a rotating shift work pattern. Hazard ratios and 95 % confidence intervals were calculated using Cox proportional hazards modeling adapted for the case–cohort design for years of night-shift work and the total number of nights worked. Additionally, analyses were repeated with exposures lagged by 10 and 20 years.

Results

We observed no associations with either years of night-shift work or number of nights worked during the entire employment period, irrespective of lag intervals. Findings from the age-stratified analyses were very similar to those observed for the entire study population.

Conclusions

The findings from this study provide no evidence to support the hypothesis that shift work increases breast cancer risk. The positive association between shift work and breast cancer observed in Western populations, but not observed in this and other studies of the Chinese population, suggests that the effect of shift work on breast cancer risk may be different in Asian and Caucasian women.

Keywords

Breast cancer Night-shift work Shift work Dose–response 

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Copyright information

© Springer International Publishing Switzerland 2014

Authors and Affiliations

  • Wenjin Li
    • 1
  • Roberta M. Ray
    • 1
  • David B. Thomas
    • 1
  • Scott Davis
    • 1
    • 6
  • Michael Yost
    • 2
  • Norman Breslow
    • 1
    • 3
  • Dao Li Gao
    • 4
  • E. Dawn Fitzgibbons
    • 5
  • Janice E. Camp
    • 2
  • Eva Wong
    • 6
  • Karen J. Wernli
    • 5
  • Harvey Checkoway
    • 2
    • 7
  1. 1.Program in EpidemiologyFred Hutchinson Cancer Research CenterSeattleUSA
  2. 2.Department of Environmental and Occupational Health SciencesUniversity of WashingtonSeattleUSA
  3. 3.Department of BiostatisticsUniversity of WashingtonSeattleUSA
  4. 4.Department of EpidemiologyZhong Shan Hospital BranchShanghaiChina
  5. 5.Group Health Research InstituteSeattleUSA
  6. 6.Department of EpidemiologyUniversity of WashingtonSeattleUSA
  7. 7.Department of Family and Preventive MedicineUniversity of CaliforniaSan DiegoUSA

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