Work and school schedules that suit early risers could be the cause of more widespread depression among night owls, according to UK researcher Jessica O'Loughlin.
The lead author of a new, large-scale University of Exeter study, O'Loughlin said people's preference for rising early or being night owls was linked to 351 genes and therefore set at birth.
Using the UK Biobank, the researchers examined information from 60,000 adults who wore activity monitors for a week, providing data on their sleep patterns, and 150,000 adults whose mental health had been surveyed.
"We found the most robust evidence to date that morning people are less likely to be depressed and have a better well-being," O'Loughlin told Sunday Morning.
"This might be because of the way society is set up to suit those early risers with a nine to five schedule.
"We think it's because early risers are more aligned to their natural body clock and night owls are fighting their body clock to wake up early to go to work."
If social expectations that everyone should start work or school at the same time changed, happiness levels might lift for those who can barely drag themselves out of bed first thing, she said.
"Perhaps if we introduced a bit more flexibility into the day and allowed night owls to work a bit later and work a bit more suited to their body clock, maybe that would improve their mental health."
While the study focused on adults, O'Loughlin hopes more research will be done on whether children and teenagers who struggle against their natural sleep patterns face poorer mental health and well-being as a consequence.
People who went to bed and got up at the same time each day also fared better on the mental health and well-being scales, the study found.
"People who had regular sleep were less likely to report depression.
"Those that... had a bit more of a varied sleep schedule, they had poorer mental health and well-being."
The study showed morning people were protected from depression if they worked normal hours, but that protection disappeared when they worked different shifts. However, O'Loughlin said low numbers of shift workers among their research subjects meant more study was needed to confirm this finding.