Is Night Shift Work Associated with Ovarian Cancer? A Systematic Review and Meta-Analysis

Background: Night shift work has been classified as a probable carcinogen due to its disruption of circadian rhythms. However, whether night shift work can increase the risk of ovarian cancer remains unclear. Herein, we investigated this association using a systematic review and meta-analysis. Methods: We systematically searched several databases until June 2025 for relevant studies. Effect estimates were extracted and pooled using a random-effects model to calculate odds ratios (ORs) with 95% confidence intervals (CIs). Heterogeneity across studies was assessed using the I² statistic, and publication bias was assessed using Egger's regression test and funnel plot asymmetry. Results: Seven studies (eight cohorts) involving >2.5 million women were included. Overall, night shift work was not significantly associated with ovarian cancer (OR = 1.13; 95% CI: 0.96, 1.32; I² = 49%). However, significant associations were observed in case-control studies (OR = 1.36; 95% CI: 1.12, 1.66; I² = 0.8%) and in high-quality studies (OR = 1.17; 95% CI: 1.00, 1.37; I² = 52%). Sensitivity analyses suggested that exposure misclassification in some cohort studies attenuated risk estimates. No publication bias was detected (z = -0.63, p = 0.53). Conclusions: While the overall findings did not demonstrate a statistically significant association, evidence from case-control studies that collected detailed information about night shift work suggests an increased ovarian cancer risk in night shift workers. Future large-scale prospective studies with detailed exposure assessments are warranted to confirm these findings.