In total, 190,810 women were studied over 24 years to investigate the link between rotating night shift work and colorectal cancer risk.
No overall association was found between rotating night shift work duration and colorectal cancer risk in the cohorts.
In the Nurses' Health Study, long-term rotating night shift work (15+ years) was associated with an increased risk of rectal cancer ( 1.60).
For short to medium durations of rotating night shift work (1-14 years), the risk of rectal cancer did not significantly increase.
Subsite analysis revealed that while distal colon cancer and proximal colon cancer risks did not show significant increases, rectal cancer risk did increase with longer shift work duration.
Simplified
Animal and human data have suggested that shift work involving circadian disruption may be carcinogenic for humans, but epidemiological evidence for colorectal cancer remains limited. We investigated the association of rotating night shift work and colorectal cancer risk in two prospective female cohorts, the Nurses' Health Study (NHS) and NHS2, with 24 years of follow-up. In total, 190,810 women (NHS = 77,439; NHS2 = 113,371) were included in this analysis, and 1,965 incident colorectal cancer cases (NHS = 1,527; NHS2 = 438) were reported during followup (NHS: 1988-2012, NHS2: 1989-2013). We used Cox proportional hazards models adjusted for a wide range of potential confounders. We did not observe an association between rotating night work duration and colorectal cancer risk in these cohorts (NHS: 1-14 years: (HR) 1.04, 95% CI: 0.94, 1.16; 15+ years: HR 1.15, 95% CI: 0.95, 1.39; P= 0.14 and NHS2: 1-14 years: HR 0.81, 95% CI: 0.66, 0.99; 15+ years: HR 0.96, 95% CI: 0.56, 1.64 and P= 0.88). In subsite analysis in NHS, rectal cancer risk increased after long-term (15+ years) rotating night shift work (proximal colon cancer: HR 1.00, 95% CI: 0.75, 1.34, P= 0.90; distal colon cancer: HR 1.27, 95% CI: 0.87, 1.85, P= 0.32; rectal cancer: HR 1.60, 95% CI: 1.09, 2.34, P= 0.02). We found no overall evidence of an association between rotating night shift work and colorectal cancer risk in these two large cohorts of nurses. Risk for rectal cancer significantly increased with shift work duration, suggesting that long-term circadian disruption may play a role in rectal cancer development. trend trend trend trend trend
Key numbers
1.60
Rectal Cancer Increase
for rectal cancer in women with 15+ years of night shift work.
1,965
Total Colorectal Cancer Cases
Total colorectal cancer cases documented during 24 years of follow-up.
190,810
Study Cohort Size
Total number of women included from NHS and NHS2.
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