Researchers increasingly recognize sleep and circadian rhythm disturbances as important risk factors for chronic disease and poor quality of life. A substantial body of evidence demonstrates that both higher sleep quality and longer sleep duration contribute to better health.
An additional, important aspect of sleep is circadian rhythms—the natural internal clock that governs sleep–wake cycles. Researchers at the University of Southern California, Northeastern University, and Northwestern University recently published a study highlighting their collaborative work on a person-centered approach to identify distinct sleep-circadian profiles among young adults and to track how these profiles changed over a six-month period. This research provides new evidence that improves our understanding of the dynamic nature of sleep and circadian health.
What Were the Researchers Studying and Why?
Most studies examine sleep duration and quality separately from circadian rhythms and typically use cross-sectional designs that cannot capture how individuals’ sleep patterns change over time. Researchers sought to address this gap by classifying young adults into sleep-circadian status groups and examining whether individuals moved between these groups over 6 months.
The investigators also explored the relationships between sleep-circadian status group, demographic characteristics, and health outcomes, including body mass index, perceived stress, depression, health-related quality of life, and excessive daytime sleepiness. This approach allowed them to develop a detailed understanding of sleep behaviors at both individual and group levels.
How Did the Researchers Conduct the Study?
The researchers analyzed six months of data from the Intensive Longitudinal Temporal Influences on Movement & Exercise (TIME) Study. The TIME Study followed 151 young adults (average age 23.4 years) who wore smartwatches continuously and provided self-reported information through brief, real-time online surveys.
Using accelerometer data the smartwatches collected, the team measured both sleep metrics—total sleep time and wake after sleep onset—and circadian rest metrics, which included activity cycle indicators reflecting synchronization with the 24-hour day, fragmentation of rest–-activity periods, and the robustness of day–-night activity patterns.
The researchers aggregated these measures into person-level averages for months one, three, and six. Using latent transition analysis—a statistical approach that identifies clusters of people with similar behavior patterns—they classified participants into sleep-circadian status groups and examined transitions among statuses. They also captured the participants' experiences over time, including information on mental health, quality of life, and cardiometabolic risk. The team analyzed these data using latent transition analysis, multinomial logistic regression, ANOVA, and ANCOVA to understand the characteristics of individuals and groups.
What Did the Study Results Show?
The analysis revealed four distinct sleep-circadian status groups:
- Optimal Sleepers (29–34% of participants) showed high circadian synchronization, well-consolidated sleep and wake periods, robust day–night activity patterns, and adequate sleep duration (more than six hours per night).
- Restless Sleepers (5–8% of participants) had similar circadian patterns to Optimal Sleepers but with fragmented nighttime sleep (at least 30 minutes of wake after sleep onset).
- Nappers (32–37% of participants) demonstrated good circadian synchronization and minimal nighttime wake but high daytime fragmentation due to napping.
- Short Sleepers (26–31% of participants) had sleep duration of six hours or less per night with diverse circadian characteristics.
While most participants (77%) maintained their status membership across six months, nearly one-quarter (23%) transitioned between statuses. Notably, 10–13% of Optimal Sleepers and 21% of Restless Sleepers became Nappers over time. In contrast, 94–100% of Short Sleepers remained unchanged throughout the study period. The data showed that males were significantly more likely than females to be Short Sleepers rather than Optimal Sleepers at all three time points (odds ratios ranging from 7.81 to 9.50).
The researchers found that the different sleep-circadian statuses correlated with varying health outcomes. Restless Sleepers reported more days of physical dysfunction compared with both Short Sleepers and Nappers. Short Sleepers experienced more excessive daytime sleepiness than Optimal Sleepers and Nappers. Interestingly, Nappers showed health outcomes comparable to Optimal Sleepers, suggesting that napping has potential protective effects.
What Is the Potential Impact of These Findings?
This study demonstrates that sleep and circadian characteristics naturally cluster into distinct patterns within individuals and that these patterns can spontaneously change over time, even without intervention. The findings challenge the assumption that circadian rhythms are largely stable and suggest that sleep-circadian health may be more dynamic than previously recognized, particularly among young adults.
The person-centered longitudinal approach this research used could inform the development of more tailored diagnostic guidelines for sleep and circadian-related disorders that account for an individual’s fluctuations over time.
Clinicians and public health practitioners may benefit from considering the broader patterns of sleep and circadian characteristics rather than focusing solely on sleep duration. This could help them diagnose more rapidly and improve the treatment of sleep- and circadian-related disorders while helping them establish robust patient profiles for identifying and treating at-risk populations, particularly young adult males with the characteristics of Short Sleepers.
Citation
Crosley-Lyons, R., Li, J., Wang, W.-L., Wang, S. D., Huh, J., Bae, D., Intille, S. S., & Dunton, G. F. (2025). Exploring person-centered sleep and rest–activity cycle dynamics over 6 months. Journal of Sleep Research, 34(6), e14471. https://doi.org/10.1111/jsr.14471
