Proceedings of The Physiological Society

Sleep Sleep and Circadian Rhythms (London, UK) (2018) Proc Physiol Soc 42, C23

Poster Communications

Does exposure to blue light reduce sleepiness in night shift workers?

T. Dorji1, S. Sharma1, S. Lowe1, M. J. Morrell2,1,3, C. James-Harvey4

1. School of Medicine, Imperial College London, London, United Kingdom. 2. Academic Unit of Sleep and Ventilation, National Heart and Lung Institute, Imperial College London, London, United Kingdom. 3. Respiratory Biomedical Research Unit at the Royal Brompton Hospital, Imperial College London, London, United Kingdom. 4. Nuffield Department of Clinical Neurosciences, University of Oxford, London, United Kingdom.


Background: Approximately 12% of all employees in the UK undertake night shifts to serve an increasingly 24/7 modern society, according to the Labour Force Survey (2016). Night shift work is thought to cause circadian phase-shift, associated with decreased alertness, workplace accidents, diabetes and cancer.1 Light plays a crucial role in circadian rhythm entrainment and regulating melatonin release.2 Previous experiments3 have shown that blue/green light of wavelength 470-525nm shows the greatest melatonin suppression, reducing and postponing sleepiness within individuals, but this has not been explored outside controlled conditions in a real-world setting. Methods: A prospective cohort study was conducted in long-term night shift (22:00 - 06:00) workers, at a Co-op warehouse in Thurrock. Approximately 150 workers were invited to take part and those who had planned annual leave, a diagnosed sleep disorder or were non-English speaking were excluded. Participants (n=10) who gave their consent filled in two questionnaires at the start and end of each shift every day for two weeks: the Karolinska Sleepiness Scale (KSS) scored from 1-9 with 9 indicating extreme sleepiness, and the Epworth Sleepiness Scale (ESS) which is scored from 0-24 (24 being very sleepy).4,5 The first week was assigned as the baseline week in which there was no intervention. During the second week, goggles (Re-TimerTM) emitting blue-green light (500nm) were worn for 30 minutes before the start of each shift. Ethical approval was obtained from the University of Oxford CUREC. Results: KSS and ESS scores from 6 participants were analysed as median and interquartile range (IQR). Data from 4 participants were neither returned nor completed properly. The average scores of weeks 1 and 2 were compared. The median KSS score decreased from 4.5 (IQR:3) a.u in week 1 to 4 (IQR:3) a.u in week 2. The median ESS score decreased from 9.5 (IQR:5) a.u to 8 (IQR:8) a.u. Both questionnaires revealed that the workers were alert, and their sleepiness was found to be low, albeit higher than normal. It was observed that exposure to blue light may reduce self-perceived sleepiness, however further studies are needed to increase the sample size and add an effective control group. Conclusions: It is important to note that to our knowledge this is the study first to examine the direct real-world effects of blue light on subjective sleepiness in shift warehouse shift workers. The project hopes to raise awareness on improving occupational lighting, encouraging the installation of blue-enriched white lights to boost mental performance and productivity in the workplace setting.

Where applicable, experiments conform with Society ethical requirements