Research has challenged the widespread belief that shift workers gradually adjust to working nights, with sleep quality and circadian rhythms in night-shift workers found to be poorer than in those who work day shifts.
Scientists at the University of Warwick, Université Paris-Saclay, Inserm, and Assistance Publique-Hôpitaux de Paris in France used wearable technology to monitor groups of French hospital workers working day or night shifts during their working and free time.
The researchers showed that night-work significantly disrupts both sleep quality and circadian rhythms and, critically, that workers can experience such disruption even after years of night shift work.
The findings, reported in a study in the Lancet group journal eBioMedicine, are believed to be the most detailed analysis of the sleep and circadian rhythm profiles of shift workers yet attempted, and the first to also monitor body temperature.
The research also demonstrated the value of telemonitoring technology for identifying early warning signs of disease risks associated with night-shift work.
The study compared 63 night-shift workers, working three or more nights of 10 hours each per week, and 77 day-shifters alternating morning and afternoon shifts at a single university hospital (Paul Brousse Hospital in Villejuif, near Paris).
Night working and health
Both groups wore accelerometers with chest surface temperature sensors throughout the day and night for a full week, with the data collected by the research team at Université Paris-Saclay and Inserm.
Analysis by University of Warwick statisticians 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. A total of 48% of the night-shift workers had a 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 didn’t correlate with their respective chronotype, in other words their ‘morningness’ or ‘eveningness’ orientation. This meant they were not sleeping in sync 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 may help to 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, the researchers argued.
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Professor Bärbel Finkenstädt from the University of Warwick’s 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.”
Dr Julia Brettschneider of the same department added: “I think there’s a misunderstanding that night shift work is just an inconvenience, whereas it can be linked to serious health risks. 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. A better understanding of the biological mechanisms helps to find answers to this question.”
