Daytime Napping and Liver Cancer Risk: A Systematic Review and Meta-Analysis of Prospective Cohort Studies

Background: Liver cancer is a major global public health challenge, with substantial morbidity, mortality, and economic costs. Growing attention has turned to sleep-related behaviors, including daytime napping, as potential risk factors for cancer. Evidence regarding the association between daytime napping and liver cancer remains inconsistent. We, therefore, conducted a systematic review and meta-analysis to investigate this association. Methods: Several databases were searched up to 1 October 2025, for studies assessing the association between daytime napping and liver cancer. Study quality was evaluated using the Newcastle–Ottawa Scale (NOS). Pooled hazard ratio (HR) and 95% confidence interval (CI) were calculated with random-effects models. Results: Four prospective cohort studies, involving 1,281,628 participants, were included. All studies were of high methodological quality according to NOS. The pooled analysis showed a significant association between daytime napping and liver cancer risk (HR = 1.24; 95% CI: 1.07, 1.43). The results did not significantly vary by sex or region. Exploratory subgroup analyses showed similar findings across sex and region. Sensitivity analyses, performed by sequentially removing each study and recombining the remaining studies, yielded pooled HRs ranging from 1.20 to 1.29. Conclusions: Daytime napping was associated with a higher risk of liver cancer. However, residual confounding and reverse causation cannot be excluded, and whether this association reflects a causal relationship or underlying health conditions remains uncertain. Further large-scale prospective studies with detailed assessments of the frequency and duration of daytime napping are needed to confirm this association.