Light at the end of the tunnel for night shift workers

The Flinders University trial is amongst the first tightly controlled in-laboratory studies to have simultaneously evaluated circadian-lighting effects on markers of body-clock timing, work-shift cognitive performance, and sleep following an abrupt transition to night shift work.

The results of the trial have produced two papers published in the Oxford University Press SLEEP journal, finding that strategic exposure to light accelerated body-clock adjustment and improved alertness and performance, as well as sleep after a night shift.

"Circadian rhythms reflect our body's internal clocks that control the activity and timing of bodily functions, including our sleep-wake cycle," says Flinders University sleep researcher Dr Hannah Scott, author of Circadian-informed lighting improves vigilance, sleep, and subjective sleepiness during simulated night shift work.

"Shift work causes circadian disruption, for which well-timed light exposure, designed to promote alertness and facilitate circadian adjustment, is one of the most potent methods to help retime the body clock."

In Australia, around 15-16 per cent of Australian workers report being shift workers. For both men and women, rotating shifts with varying schedules each week are the most prevalent type of shift work.

Supported by the Defence Science and Technology Group through the Research Network for Undersea Decision Superiority, the findings will be of particular interest for shift workers in enclosed environments such as submarines where lighting is typically dim.

"Given the complete lack of normal day-night lighting, shift work on submarines maybe be particularly challenging for the body clock to adjust to," says Dr Scott.

"We wanted to explore the unique challenges posed by night shifts, particularly the disruption to sleep-wake schedules, which can lead to impaired mental and physical performance, poorer sleep and health issues.

"We found that the use of circadian-informed lighting promoted better improved job performance and sleep for those working irregular hours," says Dr Scott.

19 adults participated in the study, which took place in FHMRI Sleep Health's laboratory under tightly controlled conditions that simulated night work environments.

Participants were exposed to two different lighting scenarios for a period of eight days to compare how their body clock adjusted and how they performed in a series of tasks.

The circadian-informed lighting, consisted of blue-enriched and dim, blue-depleted conditions designed to help the body clock adjust to night work, whilst the traditional dim, blue-depleted lighting simulated the standard lighting conditions onboard submarines.

The research team then assessed key circadian measures including melatonin levels and core body temperature, along with other outcomes including cognitive performance and sleep.

Importantly, over four consecutive simulated night shifts, the circadian informed lighting shifted participants' body-clocks around one hour faster per day compared to the standard lighting.

Alisha Guyett, lead author of A circadian-informed lighting intervention accelerates circadian adjustment to a night work schedule in a submarine lighting environment says that the findings are very promising for night shift employers and employees.

"The overarching benefits of circadian-informed lighting on sleep and alertness are very clear from this study. Our findings suggest that strategic lighting interventions can likely be used to enhance the performance, sleep, safety and well-being of night shift workers exposed to inadequate light during their work shift," says Ms Guyett.

"The circadian-informed lighting interventions significantly accelerated participants' adjustment to night work, which could have important implications for improving the health and performance of those who regularly work night shifts."

Notably, after circadian-informed lighting, participants achieved almost one hour more of sleep compared to the standard lighting condition as well as reporting lower levels of sleepiness during their shifts.

To test alertness, participants in both lighting conditions were subjected to the Psychomotor Vigilance Task (PVT) test, a behavioural attention measure. Those in circadian-informed lighting conditions made half as many (7.4 lapses) mistakes as those in standard lighting (15.6 lapses).

Senior Flinders Health and Medical Research Institute: Sleep Health researcher Professor Peter Catcheside says: "This study highlights the importance of the circadian system and circadian friendly lighting to help alleviate some of the significant challenges of shift work.

"It adds to what we already know about the use of these interventions to help optimise workspaces for enhanced performance, safety, and well-being in the modern workforce.

"These findings have important implications for submariner lighting conditions, but also mining and other workplace environments where lighting conditions may make it more difficult for shift workers to successfully adjust their body-clocks to the work schedule," he adds.