A new study from the University of Michigan uncovers the profound impact of sleep schedules on mood. By analyzing data from fitness trackers and surveys, researchers found that aligning sleep with internal body clocks can significantly enhance emotional well-being.
As the year comes to a close and to-do lists lengthen, sleep is often the first thing people sacrifice. However, a new study led by the University of Michigan suggests that maintaining a sleep schedule aligned with our internal clocks — or circadian rhythms — can provide a powerful boost to emotional well-being, potentially mitigating symptoms associated with mood disorders.
“This is not going to solve depression. We need to be very, very clear about that,” senior author Daniel Forger, a professor in the Department of Mathematics and director of the Michigan Center for Applied and Interdisciplinary Mathematics, said in a news release. “But this is a key factor that we can actually control. We can’t control someone’s life events. We can’t control their relationships or their genetics. But what we can do is very carefully look at their individual sleep patterns and circadian rhythms to really see how that’s affecting their mood.”
The study, published in the journal npj Digital Medicine, pivots from controlled laboratory research to real-world scenarios, leveraging data from the Intern Health Study.
Funded by the National Institutes of Health, this study tracks first-year training physicians who wear fitness trackers, such as Fitbits, and complete daily mood surveys alongside quarterly depression screening questionnaires.
“[T]here’s been a tremendous amount of research coming out showing that mood affects circadian rhythms and sleep, and that circadian rhythms and sleep affect mood,” Forger added.
Using this data, Forger and his team developed algorithms to analyze how well individuals’ sleep patterns align with their circadian rhythms, linking these alignments to real-world measures of mental health.
One striking finding emerged from the Nine-Item Patient Health Questionnaire (PHQ-9), a widely used tool in depression research and clinics. When individuals’ rhythms were misaligned, their PHQ-9 scores rose significantly.
“When people start to get desynchronized, we see the PHQ-9 go up, on average, by 2.5,” Forger added. “That’s clinically important.”
Misalignments in sleep and our internal clocks can significantly impact mood, but the type of misalignment matters.
“It’s not just, ‘If you go to bed earlier, you will be happier.’ To some degree, that will be true, but it will be because your sleep schedule is aligning with your internal rhythms,” co-lead author Minki Lee, an undergraduate researcher at U-M and a 2023 Goldwater Scholar, said in the news release.
The study identified three key patterns: the central circadian clock in the brain, the peripheral circadian clock in the heart and the interns’ sleep cycles. The most significant mood disturbances occurred when the central circadian clock and sleep cycle were misaligned, particularly among shift workers.
“Specifically, the misalignment between the central circadian clock and sleep exhibited the strongest negative association with mood and depressive symptoms, including poor sleep, appetite issues and even suicidal thoughts,” added co-lead author Dae Wook Kim, a former postdoctoral fellow at U-M and now an assistant professor at the Korea Advanced Institute of Science and Technology.
These findings challenge longstanding assumptions about the uniform impact of circadian disruptions, suggesting that different physiological clocks must be considered in light of one’s lifestyle and working conditions.
“This shows us we have to look at different rhythms representing different parts of your body and consider them in light of your working conditions and your lifestyle in general,” Lee added.
The implications of this research are profound, extending beyond interns to other groups such as students, older adults and individuals diagnosed with psychiatric disorders. The ability to monitor and address these rhythms using widely accessible technology, such as fitness trackers, offers a scalable solution.
“That’s why this is scalable,” added Forger. “That’s why I think this could help tons of people.”
The study not only highlights the critical role of circadian rhythms in mental health but also opens new avenues for personalized interventions aimed at improving emotional well-being through better sleep practices.