Progress in Neuro-Psychopharmacology and Biological Psychiatry
Using blue-green light at night and blue-blockers during the day to improves adaptation to night work: A pilot study
Section snippets
Background
In our modern society, night working has become unavoidable in many fields of activities. Accordingly, an increasing number of workers suffer from the harmful consequences of working night shifts on their health (Boivin et al., 2007, Haus and Smolensky, 2006) and social life (Berger and Hobbs, 2006). Night shifts generate a misalignment between the biological clock and the sleep/wake cycle, which leads to increased sleepiness and reduced performance at night when the body is set to be asleep,
Study participants
This study conformed to international ethical standards and was approved by the CHUQ ethics committee in Québec City before written informed consent was obtained. Four male workers (46, 45, 31 and 57 years old) were recruited from the Abitibi-Bowater sawmill of La Doré, Qc, Canada. Participants reported to be in good health and non-smoker. No drug or medication consumption that could affect sleep, vigilance and/or the circadian clock was allowed. Exclusion criteria consisted of having journeyed
Materials
Melatonin assessment was performed on the night before, as well as on the fifth night of the experimental night week. For that second assessment, participants were relieved from their working duty. For both melatonin assessment nights, an hourly saliva sample was collected from 00:00 h to 08:00 h in a dim illuminated (< 5 lx) isolated room. Melatonin concentration was subsequently extracted from samples as previously described (Sasseville et al., 2006).
For sleep evaluation, the Actiwatch-L
Results
MEQ scores of participant 1, 2, 3 and 4 were 65, 58, 64 and 64 respectively. Melatonin profiles are presented in Fig. 3. After four days of experimental conditions, participant 1 showed no melatonin secretion phase shift (Fig. 3A), whereas participants 2, 3 and 4 presented a phase delay of 4:16 (Fig. 3B), 1:57 (Fig. 3C) and 1:56 (Fig. 3D) hours respectively. Individual sleep results with mean value, derived from actigraphy analysis, are presented in Table 1. A main effect was found for TST (p =
Discussion
Even with a sample of 4 workers, we were able to observe consistent improvement in terms of vigilance, performance and sleep, along with a melatonin rhythm phase shift. These observations are likely to be associated with the strategic use of adequately timed blue-green light exposure at night combined with blue-blockers during the day. In fact, melatonin secretion among three of the four participants phase shifted by at least two hours, a degree of phase shift which is not usually reported to
Conclusions
When planning modifications of the L/D cycle to facilitate adaptation to night work, focusing on the control of short wavelengths could be useful since blue-green light does not need to be as bright as white light to induce partial circadian rhythm adjustment. Moreover, blue-blockers could be worn all day, to provide “circadian darkness” and prevent acute and circadian adverse effects of bright sunlight when outside, without incapacitating drivers' vision. Even though this combined strategies
Acknowledgements
We thank Marc Audet MD and Bernard Gilbert MD for their close collaboration as well as Abitibi-Bowater for access to their installation, the Abitibi-Bowater La Doré sawmill employe for there cooperation and workers who volunteered for this study. This research was supported by “Fonds de la Recherche en Santé du Québec (FRSQ)” and “Institut de Recherche en Santé Sécurité au Travail (IRSST)”.
Competing interests: The authors may have future financial interest for the commercialization of
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