A recent study published in Psychiatry Research has found that going to bed late is associated with poorer mental health, regardless of whether individuals naturally prefer to stay up late or not. This finding suggests that late bedtimes come with psychological risks, even for those who are naturally inclined to be night owls.
The human body’s internal clock, known as the circadian rhythm, plays a critical role in regulating sleep patterns. This circadian clock is located in the brain’s hypothalamus and influences various 24-hour behaviors, including sleep timing. People generally have different sleep preferences, with some preferring to go to bed early (often referred to as “morning people” or “larks”) and others preferring to stay up late (“night owls”). This preference is known as chronotype.
Previous research has indicated that an individual’s chronotype can affect their susceptibility to mental health disorders. For instance, those with a morning preference tend to have better mental health outcomes compared to evening types. However, the impact of aligning one’s actual sleep timing with their chronotype on mental health had not been thoroughly investigated. The new study aimed to fill that gap by examining the relationship between sleep timing, chronotype, and mental health outcomes, specifically focusing on depression and generalized anxiety disorder.
“Our initial thinking was that alignment between the circadian system and sleep timing would be the preeminent factor in determining mental health, more so than timing or chronotype alone. This was based on a number of smaller studies and a theory about how the circadian system works. We wanted to test it in a large, robust data set,” said study author Jamie M. Zeitzer, a professor at Stanford University and health science specialist at the Palo Alto VA Medical Center.
For their study, the researchers utilized data from the UK Biobank, a large-scale biomedical database, to analyze the sleep patterns and mental health of a substantial cohort of middle-aged and older adults. Participants were required to wear a wrist-worn accelerometer for seven consecutive days to accurately record their activity levels and sleep timing. The study included data from 73,888 participants after excluding those with incomplete information.
The researchers categorized sleep timing based on the five consecutive hours with the lowest activity levels recorded by the accelerometers. This period, known as “L5,” was divided into quartiles representing early, intermediate, and late sleep timings. Chronotype was determined using a single question asking participants about their preference for morning or evening activities. Responses were classified into morning, intermediate, or evening types.
To assess mental health outcomes, the researchers used diagnostic codes from the International Classification of Diseases, Tenth Revision (ICD-10), focusing on any mental, behavioral, and neurodevelopmental disorders, with specific attention to depression and generalized anxiety disorder.
The findings revealed a clear association between late sleep timing and poorer mental health outcomes, regardless of chronotype. Individuals who went to bed later were more likely to have mental, behavioral, and neurodevelopmental disorders, including depression and generalized anxiety disorder. This was true even for those who naturally preferred evening activities.
One of the most surprising findings was that aligning with one’s chronotype was not the best choice for everyone’s mental health. The researchers initially hypothesized that people would fare better mentally if their sleep patterns matched their natural preferences. However, the data showed that it was actually better for night owls to lead a misaligned life. Zeitzer recalled, “I thought, ‘Let’s try to disprove it, because this doesn’t make any sense.’ We spent six months trying to disprove it, and we couldn’t.”
The results were clear—both morning types and evening types who went to sleep late had higher rates of mental health disorders, including depression and anxiety. “The worst-case scenario is definitely the late-night people staying up late,” Zeitzer said. Night owls being true to their chronotype were 20% to 40% more likely to have been diagnosed with a mental health disorder, compared with night owls following an early or intermediate sleep schedule.
“We were very surprised that alignment between circadian preference and actual sleep timing was not as important as being awake late,” Zeitzer told PsyPost. “We still think that alignment is important, it may just be that the negative impact of late night behavior may be more so.”
The researchers further found that sleep duration and consistency of sleep timing could not account for these differences in mental health. This indicates that simply getting enough sleep or maintaining a regular sleep schedule is not sufficient to mitigate the risks associated with late sleep timing.
To test whether poor mental health might be causing people to stay up late, rather than late sleep timing leading to poor mental health, the researchers tracked a subset of participants who had no previous diagnosis of a mental disorder over the next eight years. This longitudinal analysis found that night owls who consistently slept late were the most likely to develop a mental health disorder during that period.
“Staying up late, even if it is your preferred timing, comes with psychological risks,” Zeitzer explained. “The ‘why’ is currently unanswered but being aware of risks is important. If you are staying awake past 1am, I would make sure that when you do so, there are psychological positives associated with such behavior – does it make you feel better? Are you being more social? Isolating behavior after 1am is likely particularly bad for your psychological health.”
While the study provides valuable insights into the relationship between sleep timing, chronotype, and mental health, it is not without limitations. The study population was predominantly Caucasian and older, which may limit the generalizability of the findings to other racial or ethnic groups.
“This was done in a middle- and older-age cohort,” Zeitzer noted. “Whether this applies to young adults or children is not known. It was also done in individuals in the UK. Whether this applies to other cultures is unclear. The 1am recommendation is also likely culturally dependent as some cultures are shifted to a later time.”
The cross-sectional nature of part of the study design also means that causality cannot be definitively established. While the longitudinal analysis helps to address this issue by examining the development of new mental health disorders over time, further research is needed to fully understand the causal mechanisms.
“We have not identified what it is about being awake past 1am that is crucial,” Zeitzer said. “It is likely that certain late night behaviors are fine while others are more associated with poorer psychological health. Whether these are causing the poorer psychological health or a manifestation of such is also unknown.”
Future studies could investigate the underlying biological and psychological mechanisms that link late sleep timing to poorer mental health. One hypothesis is that being awake late at night may impair decision-making and increase the likelihood of engaging in impulsive or maladaptive behaviors, which could negatively impact mental health.
“We would like to address the last set of caveats,” Zeitzer said. “That is, are there certain behaviors late at night that are protective of psychological health while others are more damaging? This would enable us to give more positive recommendations.”
The study, “Perils of the nighttime: Impact of behavioral timing and preference on mental health in 73,888 community-dwelling adults,” was authored by Renske Lok, Lara Weed, Joseph Winer, and Jamie M. Zeitzer.