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Disruptions to body clock linked to mood disorders in shift workers

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Disrupting the body’s internal clock – such as by doing regular night shifts – has been linked to increased risk of depression and reduced all-round wellbeing in a major new UK study.

The study, published in The Lancet Psychiatry, is said to be the largest to date to explore the impact of disturbing the body’s “circadian rhythms” – the normal pattern of activity and rest that people experience every 24 hours.

“We found a robust association between disruption of circadian rhythms and mood disorders”

Laura Lyall

Researchers from the University of Glasgow found that interrupting these patterns was linked to a range of adverse outcomes, including increased risk of depression and bipolar disorder.

People who experienced disruption to their circadian rhythms were more likely to be dissatisfied with their all-round health, were generally less happy and more likely to say they felt lonely. They also had slower reaction times.

The researchers used data on more than 91,000 people from the UK Biobank to measure their daily patterns of activity and rest or “relative amplitude”.

All participants wore accelerometers for seven days to record their activity and completed questionnaires to assess mental health, wellbeing and cognitive function.

Even after adjusting for various factors including age, sex, lifestyle and childhood trauma, the researchers found those with a lower relative amplitude – more disruption – were at greater risk of poorer mental health.

“Relative amplitude might be useful for identifying people at greater risk of major depressive disorder or bipolar disorder”

Study authors

Lead author Laura Lyall said the study was particularly significant given its scale. “In the largest such study ever conducted, we found a robust association between disruption of circadian rhythms and mood disorders,” she said.

“Previous studies have identified associations between disrupted circadian rhythms and poor mental health, but these were on relatively small samples,” she said.

Meanwhile, previous research linking disrupted circadian rhythms and poor mental health typically relied on participants accurately reporting sleep patterns and the amount of activity they did, rather than using a device to measure activity objectively.

While the study demonstrates clear links between altered circadian rhythms and wellbeing, it was not possible to identify cause and effect, the researchers noted.

“These are observational associations and cannot tell us whether mood disorders and reduced wellbeing cause disturbed rest-activity patterns, or whether disturbed circadian rhythmicity make people vulnerable to mood disorders and poorer wellbeing,” said Ms Lyall.

“To look at this in more detail, it would be useful for future studies to track participants’ rest-activity patterns over time to see whether disturbed rhythms can predict whether someone is more likely to develop a mood disorder,” she added.

The researchers suggested that using accelerometers to measure relative amplitude could even help clinicians predict patients’ likelihood of developing a range of conditions.

“Our results also highlight the potential usefulness accelerometry-derived relative amplitude as a marker of susceptibility to negative mental health and wellbeing outcomes,” said the researchers.

“Relative amplitude is relatively cheaply and easily measured and might be useful for identifying people at greater risk of major depressive disorder or bipolar disorder, or subgroups of patients who might benefit from therapies aimed at improving circadian rhythmicity,” they said.

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Readers' comments (1)

  • As many nursing staff are forced to work days and nights in the same week I would think it impossible not to interfere with every system in the body. It is time this practice was outlawed and sufficient staff put in place to provide adequate cover so nursing staff can work night duty in blocks of at least two weeks with an extra day off to acclimatise back to day duty.

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