Cancer
Night shift work and risk of colorectal cancer: results from a prospective cohort study among 56,490 female nurses in the Netherlands Linske de Bruijn* Linske de Bruijn Nina E. Berentzen Jelle J. Vlaanderen Roel C.H. Vermeulen Hans Kromhout Katarzyna Flora E. van Leeuwen Michael Schaapveld
Introduction: Shift work that involves night shifts has been classified as probably carcinogenic to humans, possibly related to the suppression of melatonin secretion. Although experimental studies suggest that melatonin inhibits intestinal tumor proliferation, epidemiological evidence for a relationship between night shift work and colorectal cancer (CRC) risk is lacking.
Methods: We prospectively examined the association between night shift work exposure and CRC in the Nightingale study. In 2011, 59,947 Dutch female nurses completed a questionnaire, including lifetime occupational history with detailed information on night shift work. Up to July 2021, 312 incident CRCs were recorded. Age-adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for associations between night shift work exposure variables and CRC risk were estimated using Cox regressions.
Results: The analysis included 56,490 nurses of whom 81% ever worked night shifts for a mean duration of 11.8 (SD=8.4) years. Compared with nurses who never worked night shifts, the risk of CRC for nurses who ever worked night shifts was slightly above the null (HR=1.15; 95%CI=0.85-1.54). A longer duration of working night shifts (≤9, 10-19, ≥20 years) and lifetime cumulative number of night shifts (tertiles in cases: 1-432; 433-1080; >1080 shifts) were not associated with CRC risk. Chronotype did not affect the associations of CRC risk with any shift work variable.
Conclusion: Our results suggest that exposure to longer durations of night shift work, as well as exposure to different measures of cumulative lifetime night shift work, are not associated with CRC risk. Our study does not provide further evidence for an association between night shift work and CRC.