Associations between shift work and risk of colorectal cancer in two German cohort studies

ABSTRACT

The association between shift work and the risk of colorectal cancer (CRC) is still unclear. Therefore, we studied the associations between exposure to shift or night work and incident CRC in two German population-based cohort studies, the Heinz Nixdorf Recall Study (HNR) and the Study of Health in Pomerania (SHIP). Including up to 6,903 participants, we analyzed the cohorts pooled and individually. We estimated incidence rate ratios (IRRs) with adjusted log-linear Poisson regression models with the natural logarithm of person-years as offset and performed subgroup analyses by sex and tumor localization in HNR. The pooled analysis revealed no increased risks for men working in night shifts (IRR: 1.03, 95% CI: 0.62; 1.71). In male HNR participants, we found an increased risk estimate for cancer of the distal colon in shift workers (IRR: 1.60, 95% CI: 0.53; 4.87) and in shift workers who did not perform night work (IRR: 3.93, 95% CI: 0.98; 15.70), but not in night workers. In SHIP, we observed elevated CRC risk estimates for rotating shift work including night work (IRR: 1.45, 95% CI: 0.72; 2.92) and for long-term exposure (IRR: 1.79, 95% CI: 0.81; 3.92) for men. In conclusion, night-shift work was not associated with CRC, although an increased risk was suggested for rotating shift work including nights in SHIP. The heterogeneity of shift-work jobs and schedules and associated lifestyle factors should be taken into account to disentangle a possible relationship between shift work and the risk for CRC in future investigations.

KEYWORDS:

• Circadian disruption
• night work
• Heinz Nixdorf Recall Study
• Study of Health in Pomerania
• risk factor

Acknowledgments

We would like to thank the investigative groups and the entire study staff of the Heinz Nixdorf Recall Study and the Study of Health in Pomerania. We also commemorate the late Evelyn Heinze at IPA for data management and performance of descriptive analyses.

Disclosure of interest

The authors report no conflict of interest. KW, SR, TB, and TBr, as staff of the Institute for Prevention and Occupational Medicine (IPA), are employed at the “Berufsgenossenschaft Rohstoffe und chemische Industrie” (BG RCI), a public body, which is a member of the study’s main sponsor, the German Social Accident Insurance. IPA is an independent research institute of the Ruhr-Universität Bochum. The authors are independent from the German Social Accident Insurance in study design, access to the collected data, responsibility for data analysis and interpretation, and the right to publish. The views expressed in this paper are those of the authors and not necessarily those of the sponsor.

Supplementary material

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Additional information

Funding

The HNR follow-up was funded by the German Social Accident Insurance (DGUV) (grant number FP 295). We thank the Heinz Nixdorf Foundation (Germany) for the generous support of the Heinz Nixdorf Study. This study was also supported by the German Ministry of Education and Science (BMBF) and the Kulturstiftung Essen. The German Research Foundation supported the study (DFG project: ER 155/6-2) and funded the study of psychosocial factors (DFG project SI 236/8-1 and SI 236/9-1).SHIP is part of the Community Medicine Net of the University Medicine Greifswald, which is supported by the German Federal State of Mecklenburg-West Pomerania.