IARC 60th Anniversary - 19-21 May 2026
Session : 20/05/26 - Posters
Night shift work and risk of colorectal cancer in the Norwegian Offshore Petroleum Workers cohort
BABIGUMIRA R. 1,2, INGER KRISTIN L. 3, MARIT B V. 2, TOM K G. 1, STENEHJEM J. 1,2
1 Dept. of Research, Cancer Registry of Norway, Norwegian Institute of Public Health, Oslo, Norway; 2 Dept. of Biostatistics, Oslo Centre for Biostatistics and Epidemiology, University of Oslo, Oslo, Norway; 3 Dept. of Registration, Cancer Registry of Norway, Norwegian Institute of Public Health, Oslo, Norway
Background: Night shift work (NSW) is classified as a probable carcinogen by the International Agency for Research on Cancer, mainly based on studies in female nurses where exposure contrasts between NSW and day work have been relatively weak. The existing evidence for an association between NSW and colorectal cancer (CRC) is limited, and there is a need for further study with high-quality NSW data. In the offshore petroleum industry, workers are exposed both to extreme NSW schedules (14 day shifts, 14 night shifts, or 14 rollover shifts [7 days + 7 nights or vice versa]). We have previously found support for an association between long duration of rollover shifts and risk of aggressive prostate cancer and suggestively so for male breast cancer in the Norwegian Offshore Petroleum Workers (NOPW) cohort.
Objective: To investigate the association between NSW and CRC risk, overall and by anatomical subtypes, in the NOPW cohort.
Methods: Among the 25,347 men in the NOPW cohort with offshore work history between 1965 and 1998, we identified 469 CRC cases 1999–2021 and compared them with 2031 non-cases drawn from the cohort in case-cohort analyses. NSW information for each job was retrieved before start of follow-up from self-reported work histories. NSW was categorized as day only, night only, rollover shifts only, and mixed (combinations of day, night or rollover). Duration was calculated as years within each category and split in quartiles, with quartile 4 split by the median. Weighted Cox regression was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for overall CRC and anatomical subtypes (right- and left-sided colon cancer and rectal cancer), adjusted for age and education.
Results: The most common shift schedules were day shift (38%) and rollover shift (33%), while only 1.5% worked night (mixed schedule=16%, missing=11.5%). For rollover shift, increased risks were seen with increasing duration for CRC overall and for right-sided colon cancer, but less clear for left-sided colon cancer and not for rectum. For CRC overall, we found a HR=1.73 (95% CI: 1.14–2.64) for the highest category of rollover duration (20–34 years) vs. day shift only. For right-sided colon cancer, the corresponding HR was 2.98 (95% CI: 1.49–5.99).
Conclusions/Implications for practice or policy: Our results suggest that risks of CRC, and particularly right-sided colon cancer, increased with increasing duration of rollover shift work in male offshore workers. These results add to the existing literature and point at extreme NSW as a possible etiological factor for CRC.