Sleep duration and the risk of prostate cancer: the Ohsaki Cohort Study.

In a prospective study of prostate cancer incidence (127 cases), among 22 320 Japanese men, sleep duration was associated with lower risk; the multivariate hazard ratio of men who slept >or=9 h per day compared with those who slept less was 0.48 (95% confidence interval: 0.29-0.79, P for trend=0.02).