Irregular bedtimes increase the risk of developing conditions ranging from depression to bipolar disorder, data from 100,000 UK Biobank participants suggest.
Summary
Activity data from 100,000 UK Biobank participants suggest that people with irregular bedtimes have a higher risk of developing mental health conditions such as depression – even if they sleep the recommended seven to nine hours.
People who go to bed and wake up at vastly different times every day are more likely to develop a mental health condition – even if they get enough sleep overall. “Eight erratic hours slept are not comparable to eight consistent hours,” suggests Christian Holz from ETH Zurich in Switzerland after analysing 100,000 UK Biobank participants’ sleeping habits.
Duration matters – but consistency matters more
Eight erratic hours slept are not comparable to eight consistent hours.
Professor Christian Holz, ETH Zurich, Switzerland
People who sleep the recommended seven to nine hours each night are less likely to develop diabetes, dementia and many other chronic conditions than people who sleep a lot less or more. But having regular bedtimes might be just as important, at least when it comes to mental health.
Holz and his colleague found that sleeping around eight hours minimises the risk of developing conditions ranging from depression to bipolar disorder – but only if the rest spans at least the same seven hours each night.
Activity tracker data from 100,000 UK Biobank participants revealed that many only slept the same five hours each night
The results come from an analysis of sleep data from 100,000 UK Biobank participants who wore an activity tracker for a week. “While people slept 8.9 hours on average, they were only reliably asleep during the same 4.8 hours each night,” Holz says. More than 25% of participants changed their sleep schedules on weekends.
According to the researchers’ estimate, 23% fewer people would develop mental health disorders in the future if everyone stuck to regular bedtimes (on top of getting enough sleep). “If people would hit seven to nine hours average duration without any focus on consistency, we only saw a 3% reduction in mental disorder incidents downstream,” Holz says.
Steady sleep schedules for mental health
Why regular bedtimes are linked to better mental health isn’t clear yet. Holz hypothesises that it might be most beneficial for our natural circadian rhythm.
Sleep is an accessible biomarker of general health.
Dr Shreejoy Tripathy, University of Toronto, Canada
And whether inconsistent sleep directly worsens mental health over time, or whether declining mental health leads to having inconsistent bedtimes, will be difficult to tease apart, says neuroinformatics researcher Shreejoy Tripathy from Canada’s University of Toronto. “The scientific establishment has yet to do that.”
Tripathy’s own analysis of UK Biobank data previously showed that people living with a mental health condition often have poorer sleep quality, even if they sleep as much as healthy people. He suggests that more doctors should be asking their patients about their sleep: “Sleep is an accessible biomarker of general health.”
Doing sleep research prompted both Holz and Tripathy to examine their own habits. “For me, the biggest thing was to stop drinking alcohol right before I went to bed,” Tripathy recalls. “My sleep improved more or less instantly.”
“I’m not at the optimum that we propose in the article,” Holz laughs. “Sometimes it’s very hard to stay consistent because there’s so many demands on us. But if you’re at the lower end of the routine hours, maybe you should ask yourself: What can you do to improve this a little bit without it costing too much?”
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- BMC Public Health, November 2025
