How many monthly nighttime-sleep opportunities are optimal for recovery from fatigue among shift-working nurses? A 1-month sleep log observational study to test anchor nighttime sleep in Japan.

Background: Given that nighttime sleep has more recuperative power than daytime sleep, ensuring the former is important to recovery from work, especially for shift-working nurses. In this 1-month sleep log study, we preliminarily examined how the number of monthly nighttime-sleep opportunities relates to fatigue-related outcomes among shift-working nurses. Methods: 526 nurses were required to record their daily sleep duration immediately after waking from sleep for 1 month. We analysed the associations among the four sleep groups (ie, ≤ 12, 13-19, 20-24 and≥24 nighttime-sleep opportunities per month) and fatigue-related outcomes. A one-way analysis of covariance or generalised linear mixed model (factor: sleep group) was conducted using R (version 4.2.2.) to test the association. Results: Significant differences among the four sleep groups were obtained using the excessive fatigue symptom inventory (EFSI), Pittsburgh sleep quality index (PSQI) and the numbers of near-miss incidents. Moreover, significant linear trends were observed in the EFSI and PSQI scores. Conclusions: Shift-working nurses who experienced 12 or fewer monthly nighttime-sleep opportunities showed worse fatigue-related outcomes than those who had sufficient monthly nighttime-sleep opportunities. Therefore, more attention should be paid to ensuring monthly nighttime-sleep opportunities when creating a shift schedule.