WE ALL love a weekend lie-in, but could a longer snooze on a Sunday morning be pushing you towards the blues?
That’s the suggestion from a new US study that found when you sleep is just as important as how much shut-eye you get.
People who don’t stick to regular sleeping and waking times are more likely to become depressed than those who do, the findings, just published in the journal NPJ Digital Medicine, and conducted by researchers at the University of Michigan, found.
"This is the first time that a study has shown clearly that disturbed sleep, not necessarily less sleep, can lower mood," Srijan Sen, a professor of depression and neurosciences and director of the University of Michigan Depression Center, says.
The findings were based on the sleep pattern of 2,100 student doctors, who were tracked for a year using digital devices (a Fitbit or an Apple watch) that detected periods of sleep and wakefulness. The students also recorded how they felt every day on a smartphone app, rating on a scale of one to ten their mood that day.
Before the start of the study and then every three months, the young doctors also filled in symptom questionnaires that are used clinically to diagnose depression.
The medical students whose sleeping schedule shifted the most – ie varied by one to two hours a night, and/or had later waking times on the weekends – were more likely to score higher on the questionnaires and to have lower daily mood ratings.
Those who regularly stayed up late, or got the fewest hours of sleep, also scored higher on depression symptoms and lower on daily mood.
Commenting on the findings, Kevin Morgan, a professor of psychology and director of the Clinical Sleep Research Unit at Loughborough University in England, says that the research adds to what’s already known about the association between sleep, daily mood and long-term risk of depression.
"If you are depressed, you almost certainly have sleep problems," he says. "If you are not depressed but have long-standing insomnia, you can be up to three times more likely to develop depression."
And, for some people, a shift to their sleep patterns is all it takes to push them into depression, adds consultant psychiatrist Dr Natasha Bijlani.
"I always encourage people to stick to the same sleeping schedule if they can, but life isn’t always like that," she says. "If you change your schedule between one to two hours outside normal times for sleeping and waking once or twice a week, it probably won’t have much of an effect. But sleeping in until noon on weekends, when you normally get up at 7am, could be enough to knock you off-kilter.
"I have lots of clients who have coped with stressful lives, but this level of disruption to their sleep and wake cycles is enough to push them over the edge."
So why should topsy-turvy sleep patterns lead to low mood or depression? One theory is that the circadian rhythm (our body clock which regulates sleep and waking cycles) goes out of kilter, disrupting the production of chemical messengers that, in turn, alter brain function and the nervous system.
"You can end up with a jet lag phenomenon where your body doesn’t know when it should be asleep and when it should be awake," says Prof Morgan.
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