J Sleep Med.  2019 Jun;16(1):26-35. 10.13078/jsm.19026.

Effects of Light on Daytime Sleep in 12 Hours Night Shift Workers: A Field Study

• Choi SJ
• Park HR
• Joo EY

• KMID: 2452866
• DOI: http://doi.org/10.13078/jsm.19026

Abstract

OBJECTIVES
Night shift workers suffer from sleep and daytime disturbances due to circadian misalignment. To investigate the role of environmental light in daytime sleep following 12 h-night shift work.
METHODS
We enrolled 12 h-shift female nurses working at one university-affiliated hospital (n=10, mean age 26.6 years, shift work duration 3.8 years). This is a cross-over study to compare sleep between under light exposure (30 lux) and in the dark (<5 lux) following 12 h-night duty. Two sessions of experiments were underwent and the interval between sessions was about a month. Psychomotor vigilance test (PVT) had performed on awakening from sleep at each session and sleep-wake pattern had been monitored by actigraphy throughout the study period. Daytime sleep was also compared with night sleep of age-and gender matched daytime workers (n=10).
RESULTS
Sleep parameters and PVT scores were not different between two light conditions. Activities during sleep seemed to be more abundant under 30 lux condition than in the dark, which was not significant. Compared to night sleep, daytime sleep of shift workers was different in terms of rapid eye movement (REM) sleep. Three shift workers showed sleep onset REM sleep and first REM sleep period was the longest during daytime sleep.
CONCLUSIONS
Unexpectedly, daytime sleep of 12 h night shift workers was well-maintained regardless of light exposure. Early occurrence of REM sleep and shorter sleep latency during daytime sleep suggest that shift workers meet with misalignment of circadian rhythm as well as increased homeostatic sleep pressure drive.

Keyword

Shift work; Light exposure; Polysomnography; Sleep; Alertness

MeSH Terms

Actigraphy
Circadian Rhythm
Cross-Over Studies
Female
Humans
Polysomnography
Sleep, REM