Circadian Disruption from Night-shift Work and Colorectal Cancer Risk: A Systematic Review and Meta-analysis

Background: Night-shift work significantly disrupts the circadian rhythm and has been classified by the International Agency for Research on Cancer as a probable human carcinogen. However, evidence regarding its association with colorectal cancer (CRC) remains inconsistent. This systematic review and meta-analysis aimed to assess the relationship between night-shift work and the risk of CRC. Methods: Following PRISMA 2020 guidelines, registered with PROSPERO (CRD420251014202), we systematically searched PubMed, ProQuest, PsycINFO, Cochrane Library, and Google Scholar for cohort and case-control studies published between January 2020 and March 2025. Studies assessing night-shift work exposure with CRC outcomes and effect estimates were included. Study quality was assessed using the Newcastle-Ottawa Scale. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated using fixed- effects models, with subgroup, sensitivity and dose-response analyses. Results: Five studies involving 143,058 participants were included. Meta-analysis demonstrated a significantly increased CRC risk among individuals exposed to ALAN or night- shift work (pooled OR = 1.62; 95% CI: 1.28–2.05; p < 0.001), with moderate heterogeneity (I² = 45%). Subgroup analyses revealed stronger associations among females (OR = 1.29) and European populations (OR = 1.62). A dose-response relationship was observed, with long-term exposure (≥10 years) associated with higher risk (HR = 1.64, 95% CI: 1.01–2.66). Sensitivity analyses confirmed robustness, and no significant publication bias was detected (Begg‘s test p = 0.35). Conclusion: This study suggests that night-shift work may increase the risk of colorectal cancer, highlighting circadian disruption as a potentially modifiable occupational risk factor. Future research employing objective measures of light exposure and sleep disruption is needed to clarify this association.