Working Time Society consensus statements: Evidence based interventions using light to improve circadian adaptation to working hours

Abstract

Interventions and strategies to improve health through the management of circadian (re) adaptation have been explored in the field, and in both human and animal laboratory manipulations of shiftwork. As part of an initiative by the Working Time Society (WTS) and International Committee on Occupational Health (ICOH), this review summarises the literature on the management of circadian (re) adaption using bright light treatment. Recommendations to maximise circadian adaptation are summarised for practitioners based on a variety of shiftwork schedules. In slowly rotating night shift schedules bright light appears most suitable when used in connection with the first three night shifts. These interventions are improved when combined with orange glasses (to block blue-green light exposure) for the commute home. Non-shifting strategies involve a lower dosage of light at night and promoting natural daylight exposure during the day (also recommended for day shifts) in acordance with the phase and amplitude response curves to light in humans.

The effects of bright light treatment on subjective and objective sleepiness during three consecutive night shifts among hospital nurses – a counter-balanced placebo-controlled crossover study

“…Separate ANOVA were performed for the three days before the night shifts, the three night shifts, and for the three days following the night shifts. The KSS data during the night work period were analyzed with a three-way ANOVA (GLM) with condition (red versus bright light), night (1)(2)(3) 24:00, 02:00, 04:00 and 06:00 hours) as factors. The KSS data during the three days following the night shifts were analyzed with a two-way ANOVA (GLM) using condition (red versus bright light) and day (mean KSS values while awake from 10:00-20:00 hours during days 7-9) as factors.…”

“…However, adaptation to night work may lead to problems when the worker wants to adapt back to a normal day-night rhythm during time off or if the work schedule also includes day work. Thus, use of bright light may be most appropriate when shift workers have several consecutive night shifts (2,6). The effect of light depends on the timing of exposure relative to the nadir of the endogenous rhythm of the person's biological clock, which is usually 1-2 hours before the habitual time of natural awakening (13).…”

“…Even though it seems evident that timed bright light will facilitate circadian adaptation to night work, and thereby improve alertness and recovery (2,6), several issues remain unsolved. Most previous studies have been well-controlled laboratory-based experiments.…”

“…This lack of restrictions at and off work is likely to explain why bright light is more effective in laboratory studies where such restrictions are common (16). For instance, it is shown that being exposed to daylight on the way home from work in the morning will impede adaptation to night work (2). Nurses who stay in shift work assumingly cope better with night work than those who quit; hence, another explanation may be that the participants could have represented healthy shift workers (25), where the therapeutic potential of light therapy would have been expected to be limited.…”

International consensus statements on non-standard working time arrangements and occupational health and safety

“…While acknowledging that the understanding of shiftwork tolerance is limited in the current body of evidence, the authors offer a number of practical solutions for employers and employees to mitigate the harmful effects of shiftwork at the level of individuals. Evidence based interventions using light to improve circadian adaptation to working hours . Lowden and colleagues27 ) discuss the significant role that light plays in entraining circadian rhythms and how exposure to light at night, as is common among shift workers, can have adverse health and safety implications. The authors review human and animal laboratory studies to highlight effective use of lighting strategies, including timing and intensity, to adapt and realign circadian rhythms. A multi-level approach to managing occupational sleep-related fatigue .…”