Proceedings of The Physiological Society

Sleep Sleep and Circadian Rhythms (London, UK) (2018) Proc Physiol Soc 42, C22

Poster Communications

Can blue light exposure influence mood in night shift workers?

W. Kim1, W. Han1, T. Rose1, C. James-Harvey2, M. J. Morrell1,3,4

1. Clinical Research and Innovation Theme, Imperial College School of Medicine, London, United Kingdom. 2. Nuffield Department of Clinical Neurosciences, Sleep & Circadian Neuroscience Institute, University of Oxford, Oxford, United Kingdom. 3. National Institute for Health Research Respiratory Disease Biomedical Research Unit, Royal Brompton and Harefield National Health Service Foundation Trust, London, United Kingdom. 4. Imperial College, London, United Kingdom.


Background: Night-shift work is becoming more common as society moves towards services being available 24 hours a day. This is problematic as poor sleep quality in shift workers can lead to mood disorders such as depression and seasonal affective disorder. Phototherapy can be used to treat mood disorders that originate from circadian disruption. One form of phototherapy is the Re-timer light therapy glasses, which emit 500nm of blue-green light. Although the glasses have been shown to be effective in phase-shifting circadian rhythms, it is not known if they are effective in improving sleep or other downstream processes such as mood changes. We aimed to investigate whether the glasses had an effect on the mood of a cohort of night shift workers. Methods: A hypothesis generating, prospective cohort study was conducted in permanent night-shift workers at a supermarket distribution warehouse. Of the 200 warehouse workers working nights, 150 visited the ‘nightclub' project*. Volunteers were given the glasses and data was collected in 6 night shift workers. Workers were excluded if they had any photosensitive conditions such as epilepsy or were unable to wear the glasses for safety reasons. The positive and negative affect schedule (PANAS) generates a positive and negative arbitrary mood score, and was used to monitor mood, on a twice-daily basis for 18 days. After 9 days of baseline monitoring, phototherapy was administered via the Re-timer glasses for 30 minutes before each subsequent night-shift for another 9 days. The baseline and post-interventional mood scores were compared via a paired two sample Student's t-test. Results: There was a significant decrease in the negative mood scores with light therapy (baseline: 15.39±5.67 vs intervention: 12.88±2.98 (mean±1 SD), p<0.001). Due to the study design, monitoring phototherapy compliance was unfeasible and the participants were not blinded to the intervention. Sample size and study duration were also limited, with little information on demographic stratification. These points need to be considered in future studies. Summary: The results suggest that light therapy was was able to alleviate negative moods in night shift workers. Whether this was due to a physiological response to light or an ensuing effect from circadian stabilisation is unclear. However, these preliminary data do suggest that potential improvements in mental health of shift-workers can be achieved with light therapy. Therefore, making similar adjustments in night shift environments and increasing awareness of available therapies may have positive implications, in the interests of both employers and employees.

Where applicable, experiments conform with Society ethical requirements