Background: Poor sleep has been linked to a number of adverse health outcomes. Recent studies suggest that late bedtimes, short or long sleep durations, and poor sleep quality may impair semen quality. No study has previously explored all three factors in relation to semen quality. Results: One hundred and four men and their partners treated at three fertility clinics in Denmark between 2010 and 2012 completed an online-version of the Pittsburgh Sleep Quality Index (PSQI). The results of the semen analyses conducted at the fertility clinics were self-reported and categorised as normal or reduced. Early bedtime (< 10:30 PM) was more often associated with normal semen quality compared with both regular (10:30 PM-11:29 PM) and late (≥11:30 PM) bedtime (OR: 2.75, 95%CI: 1.1-7.1, p = 0.04 and OR: 3.97, 95%CI: 1.2-13.5, p = 0.03). Conventional sleep duration (7.5-7.99 h) was more often associated with normal semen quality than both short (7.0-7.49 h) and very short (< 7.0 h) sleep duration (OR: 1.36, 95% CI: 1.2-12.9, p = 0.03 and OR: 6.18, 95%CI: 1.6-24.2, p = 0.01). Although poor sleep quality was associated with reduced semen quality in the descriptive statistics (p = 0.04), no differences were found between optimal (PSQI ≤6) and either borderline (PSQI 7-8) or poor (PSQI ≥9) sleep quality (OR: 1.19, 95%CI: 0.4-3.4, p = 0.75 and OR: 2.43, 95%CI: 0.8-7.1, p = 0.11) in multivariate regression models. Conclusion: Early bedtimes (< 10:30 PM) and conventional sleep duration (7.5-7.99 h) were associated with selfreported normal semen quality. The role of subjective sleep quality remains uncertain.

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