No, your body can't just 'adjust' to a night shift

A study has found that a night shift really is worse for your sleep than a day shift, and that ‘adapting’ to nocturnal working hours is actually not how it works.

The University of Warwick’s research indicates that sleep quality and circadian rhythms in night shift workers are poorer than their daytime counterparts.

What’s more, the length of time you work the night shift doesn’t seem to have an impact, so it looks like the idea that your body will ‘get used to it’ after long enough could be incorrect.

While this might not sound like a huge deal, getting proper sleep is vital for maintaining good health.

Scientists at the University of Warwick partnered with those at the Université Paris-Saclay, Inserm and Assistance Publique-Hôpitaux de Paris (France), to monitor groups of French hospital staff working day or night shifts during their working and free time.

The results showed that not only does night work significantly disrupt both their sleep quality and their circadian rhythms, but also that workers can experience such problems even after years of night shift work.

The circadian rhythm is a roughly 24-hour cycle that regulates when we sleep and when we wake up, as well as our moods, our immune, metabolic, and reproductive systems, and our daily productivity and energy levels.

Think of it as being a body clock which naturally aligns with night and day – since we’re not technically nocturnal animals, working a night shift throws that clock out of whack.

And if you’re not getting good quality sleep, the knock-on effects on your health and mental wellbeing are wide-ranging and concerning – 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.

Dr Julia Brettschneider, of the University of Warwick Department of Statistics, said: ‘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.’

The study, reported in the Lancet group journal eBioMedicine, is thought to be the most detailed analysis of the sleep and circadian rhythm profiles of shift workers ever undertaken.

Researchers compared 63 night shift workers, working three or more nights of 10 hours each per week, and 77 day workers alternating morning and afternoon shifts at a single university hospital (Paul Brousse Hospital in Villejuif, near Paris).

Both groups wore accelerometers (devices that measure the vibration or acceleration of motion), with chest surface temperature sensors throughout the day and night for a week.

The devices measured movement intensity and allowed the researchers to estimate how much sleep the participants had, how regular their circadian rhythms were, and whether their sleep was disrupted by movement.

Patterns in the chest surface temperature helped researchers get an even better idea of the participants’ circadian rhythm.

After that, analysis by University of Warwick statisticians found that 48% of the night shift workers had a disrupted circadian temperature rhythm.

They also used questionnaires to determine whether the night shift workers were not sleeping in sync with their internal clocks.

Perhaps the study’s most significant finding was that this remained the case for workers who’ve been doing night shifts for many years. In fact, the more years they had been on night work, the more severe the circadian disruption, which directly contradicts the idea that people just ‘get used’ to working odd hours.

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% 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.’

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