Unravelling the association between sleep traits and reproductive cancers: A systematic review and meta-analysis

Sleep traits (duration, insomnia, chronotype, snoring) are modifiable lifestyle factors that may influence cancer risk, but their association with reproductive cancers remains unclear. We systematically searched PubMed, Scopus, and Web of Science (until 09/2024) for observational studies investigating associations between sleep traits and reproductive cancers (including breast, prostate, endometrial, epithelial ovarian). We extracted estimates from maximally adjusted models and performed random-effects and dose-response meta-analyses. This study included 62 observational studies (45 cohort, 17 case-control) from 55 publications, but cohorts were primarily considered in interpretation. Compared to a morning chronotype, evening chronotype was associated with higher risk of breast cancer (HR = 1.12; 95 %CI: 1.07-1.17; I² = 14 %; 4 cohorts) and epithelial ovarian cancer (HR = 1.15; 95 %CI: 1.02-1.29; I² = 0 %; 2 cohorts). Insomnia was associated with elevated breast cancer risk (RR = 1.23; 95 %CI: 1.01-1.50; I² = 94 %; 9 cohorts), and the association remained similar for diagnosed insomnia (RR = 1.26; 95 %CI: 1.01-1.58; I² = 96 %; 5 studies), but high between-study heterogeneity was observed and the association was lost in properly adjusted studies (RR = 1.04; 95 %CI: 0.95-1.14; I² = 41.5 %; 3 cohorts). These findings support a role for circadian disruption in carcinogenesis. Future research should use objective sleep assessments and evaluate whether modifying sleep behaviours or circadian alignment can reduce cancer risk.