Work schedule, sleep duration, insomnia, and risk of fatal prostate cancer

Background: Studies of breast cancer in women and laboratory studies provide evidence that shift work involving circadian rhythm disruption is a probable human carcinogen. However, evidence linking shift work and other circadian disruption factors to prostate cancer risk is limited.

Purpose: To examine associations of work schedule (i.e., rotating shift work, fixed night and fixed afternoon/evening shift work); sleep duration; and insomnia frequency with prostate cancer mortality.

Methods: The Cancer Prevention Study-II is a large prospective cohort study of U.S. adults. Work schedule, sleep duration, insomnia frequency, and other information was self-reported in 1982. Among 305,057 employed men, aged ≥29 years who were cancer free at baseline, there were 4974 prostate cancer deaths during follow-up through 2010. In 2013, multivariable-adjusted relative risks (RRs) and 95% CIs were computed using Cox proportional hazards regression.

Results: Work schedule and insomnia frequency were not associated with risk of fatal prostate cancer. Short sleep duration was associated with higher risk of prostate cancer during the first 8 years of follow-up, compared to 7 hours/night, the RRs (95% CIs) for 3-5 and 6 hours/night were 1.64 (1.06, 2.54), and 1.28 (0.98, 1.67), respectively. There was no association between sleep duration and fatal prostate cancer during later follow-up.

Conclusions: These results do not support associations of work schedule or insomnia frequency with prostate cancer mortality. The association between short sleep duration and higher risk of fatal prostate cancer only during the first 8 years of follow-up suggests that short sleep duration could affect later stages of prostate carcinogenesis.