Shift work and quality of sleep: effect of working in designed dynamic light

Abstract

Purpose: To examine the effect of designed dynamic light on staff's quality of sleep with regard to sleep efficiency, level of melatonin in saliva, and subjective perceptions of quality of sleep.

Methods: An intervention group working in designed dynamic light was compared with a control group working in ordinary institutional light at two comparable intensive care units (ICUs). The study included examining (1) melatonin profiles obtained from saliva samples, (2) quality of sleep in terms of sleep efficiency, number of awakenings and subjective assessment of sleep through the use of sleep monitors and sleep diaries, and (3) subjective perceptions of well-being, health, and sleep quality using a questionnaire. Light conditions were measured at both locations.

Results: A total of 113 nurses (88 %) participated. There were no significant differences between the two groups regarding personal characteristics, and no significant differences in total sleep efficiency or melatonin level were found. The intervention group felt more rested (OR 2.03, p = 0.003) and assessed their condition on awakening as better than the control group (OR 2.35, p = 0.001). Intervention-ICU nurses received far more light both during day and evening shifts compared to the control-ICU.

Conclusions: The study found no significant differences in monitored sleep efficiency and melatonin level. Nurses from the intervention-ICU subjectively assessed their sleep as more effective than participants from the control-ICU.

Keywords: Health; Melatonin; Shift work; Sleep efficiency; Sleep monitoring; Work environment.

Fig. 1

Average melatonin profiles for intervention-ICU and control-ICU. Based on all melatonin samples from an evening or night shift [9 p.m., midnight, 3 a.m., 6 a.m. (only night shifts), and awakening or before bed] and at awakening/before sleep on day shift or day off. The results were adjusted for shift, BMI, age and time of year

Fig. 2

Light measurements. Measurements were logged per minute at 150 cm above the floor level at the two ICUs during 1 week (i.e. every minute point contains an average of data from 7 days). The dashed lines representing the corridors are measurements of ten subareas (n = 10) and the solid lines represents the observation room with measurements of two subareas (n = 2)