Day and night shift schedules are associated with lower sleep quality in Evening-types

Eveningness has been suggested as a facilitating factor in adaptation to shift work, with several studies reporting evening chronotypes (E-types) as better sleepers when on night shifts. Conversely, eveningness has been associated with more sleep complaints during day shifts. However, sleep during day shifts has received limited attention in previous studies assessing chronotypes in shift workers. Environmental light exposure has also been reported to differ between chronotypes in day workers. Activity is also known to provide temporal input to the circadian clock. Therefore, the aim of this study was to compare objective sleep, light exposure and activity levels between chronotypes, both during the night and day shifts. Thirty-nine patrol police patrol officers working on a fast rotating shift schedule (mean age ± SD: 28.9 ± 3.2 yrs; 28 males) participated in this study. All subjects completed the Morningness–Eveningness Questionnaire (MEQ). Sleep and activity were monitored with actigraphy (Actiwatch-L; Mini-Mitter/Respironics, Bend, OR) for four consecutive night shifts and four consecutive day shifts (night work schedule: 00:00 h–07:00 h; day work schedule: 07:00 h–15:00 h). Sleep and activity parameters were calculated with Actiware software. MEQ scores ranged from 26 to 56; no subject was categorized as Morning-type. E-types (<i>n</i> = 13) showed significantly lower sleep efficiency, longer snooze time and spent more time awake after sleep onset than Intermediate-types (I-types, <i>n</i> = 26) for both the night and day shifts. E-types also exhibited shorter and more numerous sleep bouts. Furthermore, when napping was taken into account, E-types had shorter total sleep duration than I-types during the day shifts. E-types were more active during the first hours of their night shift when compared to I-types. Also, all participants spent more time active and had higher amount of activity per minute during day shifts when compared to night shifts. No difference was found regarding light exposure between chronotypes. In conclusion, sleep parameters revealed poorer sleep quality in E-types for both the night and day shifts. These differences could not be explained by sleep opportunity, light exposure or activity levels. This study challenges the notion that E-types adapt better to night shifts. Further studies must verify whether E-types exhibit lower sleep quality than Morning-types.

有研究表明，晚间型昼夜节律（evening chronotype，E型）可促进轮班工作适应，多项研究显示，晚间型节律者在夜班期间睡眠表现更佳。反之，日间班次期间，晚间型节律者的睡眠主诉更为多见。然而，过往针对轮班工作者昼夜节律型的相关研究中，对日间班次睡眠状况的关注较为有限。另有研究证实，日间工作者的不同昼夜节律型之间，环境光照暴露水平存在差异。此外，机体活动可向昼夜节律时钟提供时间输入信号。因此，本研究旨在对比不同昼夜节律型者在夜班与日间班次期间的客观睡眠状况、光照暴露与活动水平。本研究共纳入39名执行快速轮班制度的巡逻警务人员，平均年龄±标准差为28.9±3.2岁，其中男性28名。所有受试者均完成了清晨型-夜晚型问卷（Morningness-Eveningness Questionnaire，MEQ）。采用腕动记录仪（actigraphy，Actiwatch-L；Mini-Mitter/Respironics，美国俄勒冈州本德市）连续监测受试者4个连续夜班与4个连续日间班次期间的睡眠与活动情况，夜班排班为00:00–07:00，日间班次为07:00–15:00。睡眠与活动参数通过Actiware软件进行计算。MEQ得分范围为26至56，无受试者被归类为清晨型（Morning-type）。与中间型昼夜节律者（Intermediate-type，I型，n=26）相比，E型（n=13）在夜班与日间班次期间的睡眠效率均显著更低，打盹时长更长，睡眠起始后觉醒时间也更长。E型受试者的睡眠片段更短且频次更高。此外，若将小睡纳入考量，日间班次期间E型的总睡眠时长短于I型。与I型相比，E型在夜班最初数小时内活动量更高。同时，与夜班相比，所有受试者在日间班次期间的活动时长更长，每分钟活动量也更高。不同昼夜节律型者的光照暴露水平无显著差异。综上，睡眠参数显示，无论夜班还是日间班次，E型的睡眠质量均更差。上述差异无法通过睡眠机会、光照暴露或活动水平来解释。本研究对“E型更适应夜班”这一观点提出了挑战。未来仍需开展进一步研究，验证E型的睡眠质量是否确实低于清晨型节律者。