Introduction More than 30% of cancer deaths could be prevented by modifying or avoiding risk factors, such as unhealthy living habits, including night-shift work, daytime napping, and nighttime sleep. We aimed to investigate the independent and combined effects of these three sleep habits on cancer incidence and cancer-caused mortality among middle-aged and older Chinese in the Dongfeng-Tongji Cohort Study (27 009 retired workers were recruited from Dong-Feng Motor Corporation (DMC) in 2008, and 25 978 participants were successfully followed-up during the first follow-up period from June, 2013 to October, 2013). During 1 14 162 person-years of follow up, we identified a total of 1251 cancer cases and 379 cancer-caused deaths.
Methods Information on sleep habits, cancer incidences and mortalities were collected at baseline 2008. Self-reported cancer incidences and cancer-caused deaths were confirmed from DMC’s health-care service system, which consists of five DMC-owned hospitals that covers all retired employees. Cox proportional hazards models were used to calculate the adjusted hazard ratios and 95% confidence intervals (HRs, 95% CIs).
Results Males experienced ≥20 years of night-shift work, or no daytime napping had increased cancer incidence, when compared to males who did not have night-shift work or had daytime napping for 1~30 min [HR(95% CI)=1.27(1.01–1.59), 2.03 (1.007–4.13), respectively]. Males who slept ≥10 hours/night had a 40% increase in cancer incidence and 59% increase in cancer-caused mortality than males who slept 7~8 hours/night [HR (95% CI)=1.40(1.04–1.88) and 1.59 (1.01–2.49), respectively]. There was an interaction effect between night-shift work of ≥20 years and sleep of ≥10 hours/night on cancer incidence (Pinteraction=0.027).
Conclusion For male subjects, both long night-shift work (≥20 years) and nighttime sleep duration (≥10 hours) were independently and jointly associated with higher cancer incidence.
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