Do you bounce out of bed early in the morning full of zest and ready to go? Or do you slap the snooze alarm until the last possible second and drag your tired body to work?
Hooray if you're a morning lark because your natural sleep habits, or circadian rhythms, are aligned with traditional 8 to 5 work schedules and school drop-off times.
But it's a bummer if you're a night owl, primed to perform better in the afternoon and evening and stay up late, according to a new study published Monday in the journal Molecular Psychiatry.
The study used sleep data gathered from wrist activity monitors worn by more than 85,000 participants of the UK Biobank Study, which houses in-depth genetic and health information on more than a half a million Brits.
Researchers compared that sleep information to self-reports of mood and found that people with a misaligned sleep cycle more likely to report depression, anxiety and have fewer feelings of well-being.
"The health problems associated with being a night owl are likely a result of being a night owl living in a morning person's world, which leads to disruption in their body's circadian rhythms," said sleep specialist Kristen Knutson, an associate professor of neurology and preventive medicine at Northwestern University Feinberg School of Medicine, who was not involved in the study.
Defying our internal body clock appears to be highly associated with levels of depression, and "having a higher misalignment was associated with higher odds of depression," said study author Dr. Jessica Tyrrell, a senior lecturer at the University of Exeter Medical School in the UK.
Prior studies, including one by Knutson, have identified a relationship between depression and sleep cycles, "although the strongest evidence is from shift workers," Tyrrell said, "with some studies suggesting that these individuals have a higher prevalence of depression and lower well-being."
Good news for morning people
On the flip side, a "novel and important finding" of the study is that those who love getting up in the morning were less likely to have irregular sleep timing than night owls, Knutson said.
"if you're a morning person, then you are less likely to have depression and more likely to report a higher well-being. This may in part be due to people who are morning people are less likely to have 'social jet lag,' " Tyrrell explained.
"Social jet lag" occurs when we go to bed later and wake up later at the weekend than we do on weekdays when we have to get up for work. It's a term borrowed from the jet lag we experience when we travel between time zones, only social jet lag is the "consequence of the discrepancy between an individual's own biological rhythm and the daily timing determined by social constraints," Tyrrell explained.
Other possible reasons include more exposure to sunlight for those who rise early, Knutson said.
"Light exposure is greater among morning types and may be reduced in those with greater sleep variability. Indeed bright light therapy is a treatment for some forms of depression," she explained.
"Circadian misalignment could also lead to inadequate sleep duration and quality, which could also impair mood and exacerbate mood disorders," Knutson said.
And finally there's the chicken and egg problem, which often plagues research that can only show an association, not causation. It's also possible that people with depression have more irregular sleep schedules, which would need to be explored in future research.