Night shift workers can continue to experience sleep disruption even after years of such shift patterns, new research has revealed.
The findings have challenged the widespread belief that shift workers can adjust to night shift work, using data collected from wearable tech.
By monitoring groups of French hospital workers working day or night shifts during their working and free time, researchers have shown that night work significantly disrupts both their sleep quality and their circadian rhythms, and also that workers can experience such disruption even after years of night shift work.
The study – by the University of Warwick with Université Paris-Saclay, Inserm and Assistance Publique-Hôpitaux de Paris – gives the most detailed analysis of the sleep and circadian rhythm profiles of shift workers to date, and is the first to also monitor body temperature.
“I think there’s a misunderstanding that night shift work is just an inconvenience, whereas it can be linked to serious health risks,” said Dr Julia Brettschneider of the University of Warwick Department of Statistics.
“We can’t avoid shift work for many professions, like healthcare workers, so we should be thinking about what can be done in terms of real-world adjustments to improve working conditions and schedules of shift workers.”
The study compared 63 night-shift workers, working three or more nights of ten hours each per week, and 77 day-shifters alternating morning and afternoon shifts at a single university hospital.
Both groups wore accelerometers with chest surface temperature sensors throughout the day and night for a full week.
Analysis of interruptions to sleep and rhythmic variations in core body temperature showed that night shift workers had less than half the median regularity and quality of sleep of their day shift colleagues, with 48 per cent of the night shift workers having disrupted circadian temperature rhythm.
Using information from questionnaires on the participants’ chronotypes, they also found that the centre of sleep for those working the night shift did not correlate with their respective chronotype, showing they were not sleeping in synch with their internal clocks.
Importantly, even workers who had been on night shifts for many years still showed these negative effects on circadian and sleep health.
The more years they had been on night work, the more severe the circadian disruption, contradicting widespread assumptions about adaptation to night work.
This helps explain why previous research has linked disrupted circadian rhythms with long term health risks, including the development of cancer and cardiovascular diseases, as well as metabolic and infectious diseases.
Professor Bärbel Finkenstädt from the University of Warwick Department of Statistics said: “There’s still an assumption that if you do night work, you adjust at some stage. But you don’t. We saw that most workers compensate in terms of quantity of sleep, but not in terms of quality during the work time.”
Professor Francis Lévi, from Université Paris-Saclay, added: “Nearly 20 per cent of the night workers could not even adjust their circadian rhythms during their free time, with the severity of impairment tending to increase with the number of years of night work.
“The telemonitoring technology, and analysis methods we have set up, make it now possible to objectively evaluate circadian and sleep health in night workers in near real time, and design prevention measures for individual workers whenever necessary.”
In addition, the team has the potential in future research to look at more long-term outcomes, such as particular diseases such as cancer that have been linked to disruption of the circadian clock.
