Using blue-green light at night and blue-blockers during the day to improves adaptation to night work: A pilot study

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Abstract

Background

Bright light at night paired with darkness during the day seem to facilitate adaptation to night work. Considering the biological clock sensitive to short wavelengths, we investigated the possibility of adaptation in shift workers exposed to blue-green light at night, combined with using blue-blockers during the day.

Methods

Four sawmill shift workers were evaluated during two weeks of night shifts (control and experimental) and one week of day shifts. Throughout the experimental week, ambient light (≈ 130 lx) was supplemented with blue-green light (200 lx) from 00:00 h to: 05:00 h on Monday and Tuesday, 06:00 h on Wednesday and 07:00 h on Thursday. Blue-blockers had to be worn outside from the end of the night shift until 16:00 h. For circadian assessment, salivary melatonin profiles were obtained between 00:00 h and 08:00 h, before and after 4 experimental night shifts. Sleep was continuously monitored with actigraphy and subjective vigilance was measured at the beginning, the middle and the end of each night and day shifts. The error percentage in wood board classification was used as an index of performance.

Results

Through experimental week, melatonin profiles of 3 participants have shifted by at least 2 hours. Improvements were observed in sleep parameters and subjective vigilance from the third night (Wednesday) as performance increased on the fourth night (Thursday) from 5.14% to 1.36% of errors (p = 0.04).

Conclusions

Strategic exposure to short wavelengths at night, and/or daytime use of blue-blocker glasses, seemed to improve sleep, vigilance and performance.

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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